Veterinary Manual of Requirements and Guidelines - Vet MORAG

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Part 5A - Residues

1.   INTRODUCTION

The Agricultural and Veterinary Chemicals Code Act 1994 specifies that the APVMA must be satisfied that foodstuffs obtained from animals treated with an active constituent or chemical product must not contain residues of the active constituent or chemical, or its metabolites, which might constitute a health hazard for the consumer.

The purpose of this document is to outline the pharmacokinetic and residues data requirements for the registration of veterinary chemical products, including data that are used to establish Maximum Residue Limits (MRLs) and Withholding Periods (WHPs) for veterinary chemicals in foodstuffs of animal origin. Part of the process for establishing MRLs and WHPs involves dietary exposure assessments.

For the purpose of this document, a maximum residue limit (MRL) is defined as:

“the maximum concentration of a residue, resulting from the registered use of a veterinary chemical product, that is legally permitted or recognised as acceptable in or on human food of animal origin. The concentration is expressed in milligrams per kilogram of the commodity (or milligrams per litre in the case of a liquid commodity)”.

It should be noted that this definition is consistent with that adopted by the FAO/WHO Codex Alimentarius Committee for Residues of Veterinary Drugs in Foods, and the European Committee for Medicinal Products for Veterinary Use (CVMP). Indeed, the principles applied to setting veterinary chemical MRLs in Australia are consistent with those employed by the Joint FAO/WHO Expert Committee on Food Additives (JECFA).

Pharmacokinetic and residues data submitted in support of an application to register a veterinary chemical product are evaluated by the APVMA Chemistry and Residues Program. Where relevant, other information including recommendations made by other governments and internationally-recognised organisations are taken into consideration. Evaluations are subject to peer review. Public comment is sought when:

  1. A veterinary product containing a new active constituent is considered for registration for the first time.
  2. A veterinary product containing an APVMA-approved active constituent is first considered for use in or on a food-producing animal species.
  3. A veterinary product containing an APVMA-approved active constituent is considered for use in or on a new food-producing animal species.
  4. A veterinary product containing an APVMA-approved active constituent is used in or on a food-producing animal species via a new route of administration, or using an amended dosing regimen.

Final recommendations for MRLs and other pertinent recommendations are published in the Commonwealth of Australia Agricultural and Veterinary Chemicals Gazette (APVMA Gazette).

The APVMA’s MRL recommendations are considered by Food Standards Australia New Zealand (FSANZ) for inclusion in Part 1.4: Contaminants and Residues of the Food Standards Code, and subsequent incorporation into Australian State and Territory food legislation. Applicants should note that MRLs may be subject to reconsideration, which could be prompted by a change in the use of a chemical, or by availability of new data.

The MRLs of agricultural and veterinary chemicals, and associated substances in foods and primary feed commodities, are also set out in the APVMA’s MRL Standard: Maximum Residue Limits in Food and Animal Feedstuffs. This document includes tables listing the MRLs of agricultural and veterinary chemicals and associated substances in food commodities (Table 1), the portion of the commodity to which the MRL applies (Table 2), definitions of residues and marker residues (Table 3), MRLs for pesticides in animal feed commodities (Table 4), and uses for substances where MRLs are not necessary (Table 5). The APVMA publishes changes to the MRL Standard on a monthly basis in the APVMA Gazette.

1.1. Reference materials

Bibliographic details of documents referred to in these requirements and guidelines (including codes and standards) are given in the References and Supporting Documents section. Applicants should be aware that many of these documents are updated regularly. It is therefore important to ensure that the latest editions of reference materials are obtained.

2. TYPES OF APPLICATIONS

The pharmacokinetic and residues data elements required for an application depend upon the nature of the application. The nature of the application determines which Part 5A (Pharmacokinetics and Residues) data module will be required; each module requires a number of data elements. More detailed information on the data elements is provided in section 5.1 of this document.

2.1. Modular categories

There are five modules for Part 5A. Each module is relevant to different types of applications. The modules which are associated with each type of application may be seen in Module levels for modular categories in Volume 3.

Modules 5.1, 5.2 and 5.4 relate to the pharmacokinetic and residues data requirements for veterinary product registrations, while Modules 5.3 and 5.5 relate to residues assessments associated with permit applications. The modules are more fully explained in Module levels for modular categories in Volume 3 and also in the individual category chapters in Volume 2: Category requirements and guidelines.

Comprehensive assessment (Module 5.1) requires submission of a full pharmaco kinetic and residues data package, containing all of the data elements listed in the column titled Data Required in ‘Module levels for modular categories’ in Volume 3, according to the type of product or application in the column titled ‘Type of application’.

Reduced assessment (Module 5.2) and Limited assessment (Module 5.4) comprise a sub-set of the data elements contained in Comprehensive assessment (Module 5.1).

2.2. Fixed categories

Applications which are evaluated under a fixed category (eg Category 1) may require submission of pharmacokinetic and residues data. The level of data corresponds to Module 5.1, 5.2 or 5.4 depending on the application category, and is provided in the relevant category chapter in Category requirements and guidelines in Volume 2.

3. PRINCIPLES OF THE PHARMACOKINETIC AND RESIDUES EVALUATION

The APVMA is responsible for registering both agricultural and veterinary chemicals and has a harmonised approach to assessing the intake of residues as part of its evaluation of safety. In most countries with advanced regulatory systems, the registration of agricultural chemicals and veterinary chemicals is undertaken by different agencies and, internationally, two different but conservative approaches to assess intake have evolved. In the interest of obtaining outcomes for MRL decisions for veterinary chemicals that are aligned with those of other countries, the APVMA utilises the procedure used by JECFA for estimating MRL values, but retains its internally harmonised approach to estimating residue intakes for food safety assessment.

An overview of the approach used by the APVMA for evaluating pharmacokinetic and residues data for veterinary chemical products is provided in Figure 1.

Figure 1: Overview of the APVMA approach for evaluating pharmacokinetic and residues data.

Figure 1: Overview of the APVMA approach for evaluating pharmacokinetic and residues data

Pharmacokinetic studies

Pharmacokinetic studies conducted in the target animal species provide information on the chemical nature and concentration of residues in edible tissues and commodities derived from treated animals. These data are used to select the appropriate marker residue(s) for each edible commodity, and to define the relationship (ratio) between the marker residue(s) and total residues occurring in each edible commodity at various times after treatment. Account is taken of the pattern of residue depletion of the veterinary chemical in the target animal, and the possible persistence of residues in specific organs such as liver or kidneys. The residues data for the standard edible tissues are subjected to regression analysis: the statistical tolerance limit based on the upper 95 % confidence limit of the 95th percentile residue concentration is estimated for each tissue. Determination of the highest permissible residue concentrations for the standard tissues (MRL proposals) is an iterative process that involves calculation of the daily dietary exposure levels using the Estimated Daily Intake1(EDI). The EDI is calculated using the median concentration of residues (instead of the MRL) and the standard daily diet, which is then reconciled with the health standard (ADI).

Health standard (ADI)

As part of the toxicological assessment, the no-observable-(adverse)-effect-level (NO(A)EL) is determined with respect to the most sensitive parameter in the most sensitive appropriate test species. A safety factor is then applied to the NO(A)EL to derive the Acceptable Daily Intake (ADI). The safety factor takes into account the inherent uncertainties in extrapolating animal toxicity data to humans, and variations between individuals within the human population. It is typically assumed that humans are ten times more sensitive than the test animal, and that there is a ten-fold range of sensitivity within the human population, such that the ADI is generally 100-fold lower than the NO(A)EL, but can vary across a broad range.

Dietary exposure assessment

Subject to the proposed uses of the veterinary chemical product, the APVMA considers the standard daily diet of the average person (of 60 kg bodyweight) to contain 500 g of mammalian or poultry meat and offal (or 300 g of fish), together with 1.5 L of milk, 100 g of eggs or egg products, and 20 g of honey. These consumption figures are consistent with those used by JECFA and other international regulatory agencies.

Determination of MRLs: The ratio of the marker residue(s) to total residues for each tissue is used in the calculation the total amount of residues in the daily food basket (as reflected by the EDI), to verify that the EDI does not exceed the ADI if the proposed MRLs were to be recommended. Where the EDI exceeds the ADI, the proposed MRLs are not recommended, and further iterations are performed with (lower) MRL proposals.

Before recommending MRLs, consideration is also given to the likely level of residue that may be expected to remain in edible commodities after use of the veterinary chemical product in accordance with the principles of Good Practice in the Use of Veterinary Drugs (GPVD), and to the availability of analytical detection methods suitable for use for routine monitoring purposes. After taking account of these factors, the resultant MRLs may be lower than the highest permissible residue levels (estimated from acceptable dietary exposure), but never higher.

In certain instances, it may not be necessary to establish MRLs for a veterinary chemical product. In such cases, the veterinary chemical and its use pattern are included in Table 5 of the MRL Standard.

Estimation of withholding periods

Once MRLs have been allocated, the next step is to determine the withholding periods (WHPs). The WHP is the minimum period that needs to elapse between the last administration of the veterinary chemical product to an animal, and when the animal may be the source of produce for human consumption. Compliance with the WHP ensures that residues in edible commodities will not exceed the MRLs. The duration of the WHP is dependent on the individual pharmaceutical formulation concerned. Therefore, specific WHPs are assigned to individual veterinary chemical products on the basis of residue depletion data generated in trials using the commercial product formulation.

4. GENERAL INSTRUCTIONS

4.1. OECD Principles of Good Laboratory Practice (GLP)

The requirement for residues studies to be conducted in accordance with the OECD Principles of Good Laboratory Practice (GLP) was introduced by the APVMA on 1 January 2003. This means that both field and laboratory phases of residues studies conducted in Australia, and used to support the establishment of MRLs in foodstuffs of animal origin, must be GLP-compliant.

Applicants conducting GLP-compliant residues trials in Australia should refer to the guidance document “No.1: OECD Principles of Good Laboratory Practice” that is available at the OECD’s website http://www.oecd.org/ehs/.

For a study conducted in Australia to be GLP-compliant, it must be undertaken by GLP‑recognised testing facilities. The National Association of Testing Authorities (NATA) is the sole Australian organisation responsible for monitoring compliance with the OECD Principles of GLP. Additional information is available regarding GLP recognition in Australia at the NATA website www.nata.asn.au. Overseas studies must be conducted by GLP-recognised testing facilities covered by that country’s GLP compliance monitoring program.

Applicants should note that certain residue trials will be exempt from GLP requirements as set out below:

  1. Transitional requirement: A submission to the APVMA after 1 January 2003 may contain non-GLP compliant studies, where those studies commenced in Australia prior to 1 January 2003. Similarly, non-GLP compliant overseas studies are accepted by the APVMA, where the studies commenced prior to 1 January 2003 and were conducted in accordance with the standards of the overseas country at the time the studies were initiated. (Note: Studies that have not been conducted in accordance with the OECD Principles of GLP may be submitted in support of the proposed product registration. However, it is mandatory that the ‘critical’ residues studies be GLP-compliant).
  2. Characterisation of test items (active ingredients or formulation) for use in GLP studies need not be conducted according to the OECD Principles of GLP, but it is recommended that a laboratory accredited to ISO/IEC 17025 by NATA or a NATA mutual recognition partner be used. In this respect, some Member States of the EU may require that characterisation of test items be in accordance with GLP. Applicants intending to submit residues data to both the APVMA and these Member States may wish to comply with the standards applied by the Member States to the characterisation of test items.
  3. The GLP requirement does not apply to clinical bioequivalence or pharmacokinetic studies, or to studies on residues in fibre.
  4. The GLP requirement is not mandatory for studies in support of Permits and Minor Use approvals, however, it is strongly recommended.

4.2. Residues guidelines

The APVMA, in co-operation with peak industry bodies, has prepared a series of residues guidelines addressing specific residue requirements. The guidelines are first published in the APVMA Gazette. Some of these guidelines are referred to in the respective explanatory sections of these instructions. These and other guidelines which deal with specific residues issues are available on the APVMA website. They should be consulted and followed where relevant.

4.3. General instructions on pharmacokinetic studies, residue kinetic studies and marker residue(s) depletion trials

Where new veterinary chemical products are to be used in or on food-producing animal species, Applicants are required to submit appropriate pharmacokinetic, residue kinetic and residues depletion data, or relevant scientific argument2 in support of their application for registration. Fundamentally, the pharmacokinetic and residue kinetic data are used for MRL determinations, while the residue depletion data are used to establish WHPs.

4.3.1. Pharmacokinetic data

Pharmacokinetic data comprise information on the absorption (A) of a veterinary chemical, its distribution (D) in tissues, its metabolism (M) or biotransformation, and excretion (E) over time. It should be noted that the purpose of pharmacokinetic studies is not one of mass balance (ie to achieve quantitative recovery of the administered dose), but rather to provide information on the concentration-time profile of the veterinary chemical and its metabolites in the target animal species, and subsequent planning of residue depletion studies.

Additionally, the pharmacokinetic profiles of the veterinary chemical and its metabolites in the target animal species are compared qualitatively with those of the laboratory animal species used to establish the health standards, to verify the relevance of the toxicological effects and NOE(A)Ls, and thereby validate the dietary exposure assessments.

Pharmacokinetic data

Absorption

The primary purpose of absorption studies is to assess the bioavailability of the veterinary chemical, which relates to the rate and extent of absorption. The same considerations of absorption apply regardless of the route of administration.

In the case of veterinary chemicals where it is proven that systemic absorption is negligible (ie where metabolism studies demonstrate that the levels of total radioactive residues in edible commodities are below the Limits of Quantification [LOQ] of the analytical method used for monitoring and surveillance purposes), further residue studies are not required. However, if there is significant systemic absorption, and total radioactive residues in any of the edible commodities are above the method LOQ, then full residues studies are required.

Distribution

Following absorption, the veterinary chemicals are distributed throughout various tissues and organs of the target animal species. The results of distribution studies are useful in identifying the target tissue(s).

Metabolism

Different biotransformation products may possess different toxic potentials. Therefore, information on the chemical nature, concentration, and persistence of the total residues is required. The purpose of the metabolism study in the target animal species is to provide the necessary information on the metabolic fate of the veterinary chemical in the edible tissues, and to enable the establishment of the marker residue(s).

These studies are also necessary to establish whether the metabolite(s) found in target animals are the same as those found in the laboratory animals used for toxicity testing. This is referred to as comparative metabolism, and determines whether the metabolites that people are exposed to when consuming tissues from treated animals are also produced in the laboratory animals used to establish the health standards. This information is required to validate the approach to assessing dietary exposure and the potential risk to human health.

All the available data from any application in the target species, the test species (including in vitro systems) and - as far as available - data from human use should be considered. The studies should provide information necessary for an adequate evaluation of the metabolism of the product, including:

  • nature of the metabolite(s)
  • chemical nature of residues in edible tissues (muscle, liver, kidney, fat) and in products (milk, eggs and honey)
  • influence of the route of administration on the metabolic profile
  • relations between structure and biological activities, if available
  • bioavailability of bound metabolite(s).
Excretion

Data on excretion in target animal species is required, including renal and faecal excretion. All other routes of excretion should be considered when appropriate (eg milk). Information on the route(s) of excretion reflects the pathways by which the veterinary chemical is metabolised.

4.3.2. Residue kinetic data:

Residue kinetic studies provide information on the concentration profile of total residues in edible tissues over time, and the corresponding concentration profile of marker residue(s). These data are used to

  • define the relationship between the marker residue(s) and total residues in edible commodities at any time after treatment
  • calculate permissible residue levels (MRLs).

4.3.3. Marker residue(s) depletion trials:

The data from marker residue(s) depletion trials should show whether, and at what concentration, veterinary chemical marker residue(s) occur in edible tissues (muscle, liver, kidney, fat, injection site tissues) and commodities (eggs, milk, honey) from treated animals over time. The purpose of marker residue(s) depletion trials is to establish appropriate withholding periods (WHPs) for veterinary chemical products.

Withholding Periods (WHPs)

Marker residue(s) depletion trials must characterise enough of the decline profile to enable the necessary WHPs to be recommended with confidence. Where a nil WHP is proposed, the residues data should demonstrate compliance with the relevant MRLs at all times after treatment. The APVMA must not be called upon to extrapolate or otherwise place undue dependence on inadequate data. Residue decline trials should, therefore, be extensive enough to provide opportunity for all probable sources of variation to express themselves.

Export Slaughter Intervals (ESIs):

Where appropriate, data from a well-designed residues decline trial are also likely to be used to determine an Export Slaughter Interval (ESI) for the product. Establishment of the ESI may necessitate monitoring the residues decline profile to concentrations below the MRL or the Limit of Quantification (LOQ). Further information on this aspect is provided in Part 5B: Overseas trade aspects of residues in food commodities of the Veterinary Requirements Series.

Critical use-pattern

Residue depletion trials must be conducted using the formulation that is to be marketed in Australia, and animals must be treated in accordance with the critical use pattern specified on the draft label of the veterinary chemical product. The critical use pattern refers to the maximum dose rate to which animals may be exposed. Typically, the instructions for veterinary chemical products express dose rates in terms of a range of body weights: animals at the lower end of the bodyweight range may receive medication at a rate that exceeds the nominal dose rate. The highest rate, in terms of mg of veterinary chemical per kilogram bodyweight, is considered to be the critical dose rate.

Treatment regimens

Treatment regimens can be broadly classed as:

  • single treatments, where a veterinary chemical product is given once to an animal for a specific therapeutic effect. In this case, a single dose of veterinary chemical product (at the critical dose rate) is the appropriate exposure regimen during residues trials.
  • repeat treatments, such as endo/ecto-parasiticide treatments, where a single treatment is repeated. If a repeat dosage regimen can be reasonably anticipated in practice, even if not specified on the product label, then repeat treatments should be assessed.
  • short-term treatments, where animals are dosed for a number of days, on one or more occasions. In this case, test animals should be dosed for the maximum period permitted on the proposed label. Where the re-treatment interval is short, or veterinary chemical has a propensity to remain in edible tissues, residue trials may need to incorporate multiple treatment periods at the shortest proposed re-treatment interval.
  • long-term treatments, where animals are treated for prolonged periods eg medicated feed or water treatments, and where a nil withholding period is (often) desired. In this case, animals must be treated at the maximum proposed rate for a period that is sufficient to enable the residue concentrations in edible commodities to reach a steady-state equilibrium (ie demonstrate that residue concentrations have reached a plateau).

4.4. Application layout

A checklist of data requirements for Part 5A (Pharmacokinetics and Residues) of an application for veterinary chemical products is shown in Table 1 below, along with a brief description of how they should be set out.

Table 1: Data requirements for Part 5A

Requirement Comments

Pharmacokinetic and Residue Kinetic studies (for the determination of MRLs)

  • summary of studies
  • proposed ADI
  • proposed marker residue(s)
  • proposed target tissue(s)
  • ratios of marker residue to total residues at specified times post-treatment
  • proposed MRLs for edible commodities

A single summary of all pharmacokinetic and residue kinetic studies is required, along with an interpretation of the results, clearly outlining the reasons for the proposed marker residue(s) and target tissue(s), and the proposed MRLs for each edible commodity. Full copies of each of the studies should be provided in the appendices.

Where MRLs have already been established, details of the previously established marker residue(s), target tissue(s), ratios of marker residue(s) to total residues, and MRLs should be provided.

Marker residue(s) depletion trials (for the estimation of WHPs)

  • summary of studies
  • proposed WHP(s)

A single summary collating all the relevant residues decline data is required, along with an interpretation of the results, which give rise to the proposed WHP(s). Full copies of each of the residue decline studies should be provided in the appendices.

Analytical methodology

  • summary of the analytical method(s) and validation data for methods used in pharmacokinetic and residue kinetic studies
  • summary of the analytical method(s) and validation data for the methods used in the marker residue(s) depletion trials

Copies of the full reports for each analytical method, including validation report(s), should be provided in the appendices.

Appendices

  • copies of the full reports for pharmacokinetic, residue kinetic and residue trials should be provided, along with complete details of the analytical method(s) and validation reports.
 

5. RESIDUES DATA REQUIREMENTS

5.1. Nature of the data required

The type of pharmacokinetic, residue kinetic and marker residue(s) depletion data that should be provided in support of an application to register a veterinary chemical product will depend on whether:

  • the veterinary chemical has been previously approved by the APVMA
  • the APVMA-approved veterinary chemical has been previously registered in a product for use in or on the target animal species
  • the dose form, treatment regimen, and route of administration of the veterinary chemical product has been considered previously by the APVMA.

Details of the types of data required to address the veterinary residues aspects of an application are provided in Table 2 below, along with references to the appropriate sections within this document.

Table 2: Pharmacokinetic and residues data requirements based on the type of product application

Registration status
Data requirements (reference)
Veterinary Chemical
Use of veterinary chemical in target animal species
Dose form, route of admin istration, and treatment regimen
New veterinary chemical
(not currently approved by the APVMA)
--
--
Full pharmacokinetic, residue kinetic and residue depletion package (Sections 5.2, 5.3, 5.4)
Existing veterinary chemical
(previously approved by the APVMA)
Not currently registered
--
Full pharmacokinetic, residue kinetic and residue depletion package (Sections 5.2, 5.3, 5.4)
Existing veterinary chemical
(previously approved by the APVMA)
Currently registered by the APVMA
Not currently registered
Full pharmacokinetic, residue kinetic and residue depletion package (Sections 5.2, 5.3, 5.4)
Existing veterinary chemical
(previously approved by the APVMA ie generic registrations)
Currently registered by the APVMA
Currently registered
Residue depletion package only (Sections 5.3, 5.4)

 Only one full pharmacokinetic study per target animal species is required, using the main route of administration. Where a new route of administration is proposed, details of the original pharmacokinetic study in the target species should be provided. However, a new pharmacokinetic study employing the new route of administration is not required.

5.2. Pharmacokinetics and residue kinetics data (maximum residue limit [MRL] determination)

5.2.1. Overview

Where specified in 5.1 (above), data on the absorption, distribution, metabolism/biotransformation and excretion of a veterinary chemical, and the occurrence of its metabolites in target animals should be provided for applications to register products containing veterinary chemicals that are to be used in or on food-producing species. Only one full pharmacokinetic study per target species is required for any veterinary chemical. Where the veterinary chemical can be administered via a number of different routes, the pharmacokinetic study should be conducted employing the route most commonly used.

The purpose of the pharmacokinetic study is not one of mass balance (ie to achieve quantitative recovery of the administered dose), but rather to elucidate the chemical nature and concentration of the residues in edible tissues (muscle or muscle plus skin in normal proportion3, fat or fat plus skin3, liver, kidney), milk, eggs and honey over time.

The pharmacokinetic and residue kinetic data are used to determine the concentration of total residues and marker residue(s) for each edible commodity, and the ratios of marker residue(s) to total residues at any time between administration of the veterinary chemical product and depletion of the residues to permitted levels. Pharmacokinetic data also enable the target tissue(s) to be defined. The target tissue is the edible tissue selected to monitor the total residue in the target animal and is usually, but not necessarily, the tissue with the slowest depletion rate of the residues. When a veterinary chemical is to be used in a lactating animal or laying birds, MRLs and WHPs must be established for milk and eggs. Consequently, in these circumstances, milk and eggs are considered to be “target tissues”, in addition to the target tissue selected for residue monitoring in the edible carcass. When the veterinary chemical is to be used in bees, honey must also be considered as a “target tissue”.

In the event that chemically-bound residues are formed, it may be prudent to provide all available information on mechanisms and reversibility of their formation and, if relevant for the final assessment, their bioavailability following oral ingestion.

Marker residue(s) and target tissue(s) are selected in such ways that total residues in each edible commodity are at or below the permitted concentration if the marker residue is at or below the MRL.

5.2.2. Specific requirements:

Ratio of marker residue(s) to total residues

The applicant should measure the depletion of total veterinary chemical-related residues in edible tissues of target animals after the last administration of the veterinary chemical.

Radiotracer methodology is currently the most useful technique for determining the total veterinary chemical-related residues. However, depending on the ADI established, alternatives may be used such as a microbiological method in order to measure the total microbiologically active residues.

Samples are also assayed (using non-radiolabelled techniques) for their content of the proposed marker residue(s). The results from these residue kinetic studies must enable determination of the ratio of the marker residue to total residues without extrapolation. The ratio of marker residue(s) to total residues for each edible tissue or commodity is used in the calculation of the total amount of residues in the daily food basket (as reflected by the EDI), to verify that the EDI does not exceed the ADI if the proposed MRLs were to be recommended.

Trial design considerations

The total residue depletion (residue kinetics) study should be conducted with previously un-medicated animals that are representative of the proposed target populations. Animals of both sexes should be used if a product is intended for use in both female and male animals. After animals have been treated with the veterinary chemical, edible tissues and biological fluids should be collected at appropriate times for residue analysis.

The groups of animals used should be large enough to allow statistical assessment of the data. It is recommended that the following numbers of animals be sampled at least at each time-point:

  • large animals: 4 animals per slaughter time, at 3-5 slaughter times
  • poultry: 6 birds per slaughter time, at 3-5 slaughter times
  • fish: 10 fish per slaughter time, at 3-5 slaughter times
  • lactating cattle for milk collection: 8 animals, including animals at second or subsequent lactations (4 high yielding cattle at an early stage of lactation and 4 low yielding cattle at a late stage of lactation)
  • laying birds for egg collection: sufficient birds to collect 10 eggs per time-point
  • honey: 5 honey samples, each from a separate hive.

The results of the residue kinetic studies should indicate whether residues occur in the foodstuffs obtained from treated target animals and, if so, for how long after the application of the veterinary medicinal product.

The ratio of the marker residue to total residue should be calculated for each edible tissue or commodity, and these values should then be used to estimate appropriate permitted MRLs using the iterative approach provided in Table 3 below. Note that the sum of the estimates for each tissue (equivalent to the total amount of residues ingested) must not exceed the ADI.

For an injectable product, the depletion of residue remaining at the injection site must also be monitored and reported. For this purpose, where the size of the animal permits, the standard 500g sample of the injection site tissue (including muscle, fat and fascia tissue in natural proportions) should be collected in the shape of a cylinder. The dimensions for a cylinder containing approximately 500 g of tissue are, for an intramuscular injection, 10 cm in diameter and 6 cm in depth, and, for a subcutaneous injection, 15 cm in diameter and 2.5 cm depth. Analysis of injection site samples should be conducted on each tissue fraction (ie muscle, fat/fascia), to facilitate comparison with muscle and fat MRLs.

Table 3: Iterative approach to estimating permitted MRLs

Edible tissue or product Daily consumption (kg) Median marker residue concentration (µg/kg) Ratio of marker residue to total residue Amount of residues per edible tissue or product
Muscle (mammals, poultry, fishδ) 0.300 M1 R1 (M1 × 0.3)/R1
Fat
   Mammals    Poultry

0.050
0.090

M2
M3

R2
R3

(M2 × 0.05)/R2 (M3 × 0.09)/R3
Liver (mammals, poultry) 0.100 M4 R4 (M4 × 0.10)/R4
Kidney    Mammals    Poultry
0.050
0.010

M5
M6

R5
R6
(M5 × 0.05)/R5 (M6 × 0.01)/R6
Milk 1.50 M7 R7 (M7 × 1.50)/R7
Eggs 0.100 M8 R8 (M8 × 0.10)/R8
Honey 0.020 M9 R9 (M9 × 0.02)/R9
ADI (µg/person) Statement of the value of the relevant ADI
% Total used for veterinary products Sum of relevant fields of the last column of the above table × 100 ADI

δ  Muscle and fat in natural proportions.

 Fat and skin in natural proportion for pigs;

 Fat and skin in natural proportion;

For milk, the residues present at the level of the MRL must not affect the function of dairy starter cultures. This requirement is not a food safety issue, but is founded in the APVMA’s legislative requirement that use of a registered chemical product “would not be likely to have an unintended effect that is harmful to animals, plants or things or to the environment” [section 14(3)(e)(iii) of the Agvet Codes].

For lipophilic (fat-soluble) veterinary chemicals (log P > 44), it is general policy for an MRL to be set in fat only, and not in muscle, as any residues detected in meat samples are attributed to non-trimable fat interspersed in the muscle. In those rare cases where both muscle and fat residues are below the limit of quantification, but where an MRL is necessary for monitoring and surveillance purposes, an arbitrary MRL at the limit of quantification of the analytical method for one of these tissues is necessary.

5.3. Marker residue(s) depletion trials data (withholding periods [WHPs] estimation)

In relation to the use of a veterinary chemical product, a Withholding Period (WHP) is defined as the minimum period that needs to elapse between the last administration of the veterinary chemical product to an animal, and the slaughtering of the animal, or the collection of milk, eggs or honey from the animal for human consumption. The purpose of the WHP is to ensure that edible commodities from treated animals contain residue levels that are below the MRL.

Compliance with the WHP should provide a high degree of assurance both to the producers and the consumers that the concentrations of residues in foods derived from treated animals are below MRL.

The WHPs for animal slaughter as well as for the production of milk, eggs and honey for human consumption are determined from the results of suitable residue depletion studies using:

  • the formulation intended for marketing in Australia
  • the critical use-pattern administered to the target animal species.

5.3.1. Specific requirements

As indicated in section 4.1 of this document, all residue studies should be conducted in conformity with the OECD Principles of Good Laboratory Practice (GLP), and should follow available internationally-recognised and regularly updated test protocols.

In addition, the following detailed information should be given if applicable:

  • species/breeds/strains/source of test animals used
  • number, age, sex, body weight and production status of the dosed animals, including growth rate, milk/egg/honey yield
  • animal husbandry conditions; water and food consumption (especially for veterinary chemical products administered via drinking water and/or feed)
  • details of the formulation of the administered veterinary chemical product and method of dose preparation
  • details of the mode of dose administration (dose [expressed in mg/kg body weight], frequency of dosing, and duration) must be provided.

For the determination of withholding periods (all target species), the groups of animals used should be large enough to allow statistical assessment of the data, and be representative of the target population.

  • typically, for milk residue trials, a minimum of 20 animals is required, and selected animals need to be representative of the normal range of milk production volumes. Further, animals should be kept under normal zootechnical conditions. Milk production volumes for individual animals should be reported for each milking, and samples should be collected over a time sufficient to follow the depletion profile of the marker residue(s).
  • for tissue residue trials, contemporary standards require a minimum of five (5) animals per slaughter time. Depending on the nature of the product under investigation, not fewer than four (4) or five (5) appropriately spaced sampling times will be required to describe the residues decline profile. Standard animal husbandry conditions should be followed.
  • for residue trials with laying poultry, egg-production should be reported, and eggs collected for a sufficient period to monitor the decline profile of the marker residue(s).
  • further information on trial design considerations and analysis of the residues data to determine an appropriate withholding period can be found in the residues guidelines located on the APVMA website. Applicants are also strongly encouraged to seek advice on their trial protocols from the APVMA Veterinary Residues Team.
  • harmonisation of the APVMA’s residue data requirements with those of other international regulatory agencies means that useful information on the analysis of the residues data to determine an appropriate withholding period can also be found on the EMEA website at http://www.emea.eu.int/pdfs/vet/swp/003695en.pdf, and http://www.emea.eu.int/pdfs/vet/swp/047398en.pdf, and the USFDA website at http://www.fda.gov/cvm/Guidance/1732.htm.

5.4. Analytical methodology

The Applicant must provide complete details of the validated analytical method(s) used:

  • in pharmacokinetic and residue kinetic studies
  • for the determination of marker residue(s) in the trials conducted for the estimation of WHPs.

As a minimum, the description of the analytical method(s) must include:

  • purpose and scope
  • reagents
  • equipment
  • collection of samples
  • storage of samples
  • preparation of the laboratory sample
  • preparation and clean-up of tissue extracts
  • procedure for the determination of the residues
  • calculation of results eg method of standardisation, use of calibration curves (mathematical model, parameters, working range)
  • quality control (internal).

Appropriate validation data must be provided for the analytical method(s) used, at the concentrations of marker residue(s) in target tissue(s). The validation data must include details of:

Specificity - the ability of a method to distinguish between the analyte being measured and other substances which may be present in the sample being analysed. Details concerning specificity must relate at least to any substances which are likely to be present and to give rise to a signal when the measuring principle described is used, eg homologues, analogues and metabolic products of the residues of interest. From the details concerning specificity it must be possible to determine the extent to which the method can distinguish between the analyte and the other substances under the experimental conditions.

 

Accuracy - the closeness of agreement between the true value and the mean result, which would be obtained by applying the experimental procedure a very large number of times. Accuracy can also be determined by recovery experiments using fortified blank matrices (mutually independent replicates). For example, 18 blank test portions could be selected and 6 fortified at each analyte level.

Precision - the closeness of agreement between mutually independent test results. It covers repeatability and within-laboratory reproducibility, and results are typically expressed as the percent relative standard deviation of replicate analyses (n=6) at various concentrations of analyte.

Limit of Detection (LOD) - the LOD is the smallest measured content of an analyte from which it is possible to deduce the presence of the analyte with reasonable statistical certainty. One possible way to estimate the LOD involves determining the arithmetic mean of the analyte concentrations determined using the analytical procedure, as proposed, in a representative number of separately sourced and prepared blank samples (n ≥ 20) plus three times the standard deviation. Other methods of calculation providing substantially the same statistical certainty may be used.

Limit of Quantification (LOQ) - the LOQ corresponds to the smallest measured content of an analyte above which a determination of the analyte can be made with a specified degree of accuracy and precision.

Stability of the analyte during storage and analysis – data should be provided to demonstrate that residues of the marker residue(s) are stable when samples (tissues, eggs, milk and honey) are stored for 6 months or longer. Likewise, the stability of marker residue(s) throughout the extraction and quantification procedure needs to be demonstrated. These characteristics are important in determining that the reported residue levels are a true reflection of the levels of incurred residues.

6. GLOSSARY

Acceptable Daily Intake (ADI): the estimate of the residue, expressed in terms of micrograms or milligrams per kilogram of bodyweight, that can be ingested daily over a lifetime without any appreciable health risk.

The Codex Alimentarius Commission (Codex): the joint FAO and WHO body created in 1963 to develop food standards, guidelines and related texts such as codes of practice under the Joint FAO/WHO Food Standards Programme. The main purposes of this Programme are protecting health of the consumers and ensuring fair trade practices in the food trade, and promoting coordination of all food standards work undertaken by international governmental and non-governmental organizations.

Critical use-pattern: the maximum dose rate to which animals may be exposed (as specified on the product label). Typically, the instructions for veterinary products express dose rates in terms of a range of body weights: animals at the lower end of the bodyweight range receive medication at a rate that exceeds the nominal dose rate. The highest rate, in terms of mg of veterinary chemical per kilogram bodyweight is considered to be the critical dose rate

Daily food basket: the quantity of food consumed each day by an average person of 60 kg bodyweight. The daily food basket is taken to contain:

500 g of mammalian meat (made up of 300 g of muscle, 100 g of liver, 50 g of kidney and 50 g of fat) OR 500 g of poultry (made up of 300 g of muscle, 100 g of liver, 10 g of kidney and 90 g of skin with associated fat) OR 300 g of fish (muscle and fat in natural proportions) PLUS 1.5 L of milk PLUS 100 g of eggs or egg products PLUS 20 g of honey.

These consumption levels, in conjunction with the median residue concentration in each of the tissues, are used to estimate the total residues that may be consumed by an average person in one day. The total amount of residues in the daily food basket must not exceed the ADI.

Estimated Daily Intake (EDI): the estimate of chronic dietary exposure to residues of veterinary chemicals present in edible commodities sourced from treated animals. The estimate is calculated using the median residues concentrations and the standard daily food basket.

European Committee for Medicinal Products for Veterinary Use (CVMP): the committee responsible for preparing the European Medicines Agency’s (EMEA) opinion on questions concerning veterinary medicinal products, including assessment of the quality, safety and efficacy requirements (in accordance with EU legislation).

European Medicines Agency (EMEA): the body that coordinates the evaluation, supervision and marketing authorisation of medicinal products for both human and veterinary use throughout the European Union.

FAO/WHO Codex Alimentarius Committee for Residues of Veterinary Drugs in Foods (CCRVDF): the Codex committee that, amongst other functions, determines priorities for the consideration of residues of veterinary drugs in foods and recommends Maximum Residue Limits (MRLs) for veterinary drugs for Codex.

Food Standards Code: A set of legal national standards for the composition and labelling of food for human consumption. The standards are developed and maintained by Food Standards Australia New Zealand (FSANZ) and are enforced under individual States and Territory Food Acts. Part 1.4: Contaminants and Residues of the Food Standards Code is located at http://www.foodstandards.gov.au/foodstandardscode/index.cfm#_FSCchapter1.

Good agricultural practice (GAP) in the use of agricultural chemical products: the nationally recommended, authorised or registered use-pattern of chemicals that is necessary for effective and reliable pest control under actual conditions at any stage of production, storage, transport, distribution and processing of food commodities and animal feed.

Good practice in the use of veterinary drugs (GPVD): the officially recommended authorised usage of veterinary chemicals approved by national authorities under practical conditions (sometimes referred to as good veterinary practice - GVP).

Joint FAO/WHO Expert Committee on Food Additives (JECFA): an international scientific expert committee that is administered jointly by the Food and Agriculture Organisation of the United Nations (FAO) and the World Health Organisation (WHO). JECFA evaluates the safety of food additives, including contaminants, naturally occurring toxicants and residues of veterinary drugs in food.

Log P: the log of the octanol/water partition coefficient, which provides a measure of the lipophilicity of the veterinary chemical ie whether the chemical preferentially partitions into fat tissues.

Marker residue: the parent veterinary chemical or any of its metabolites, or a combination of any of these, with a known relationship to the concentration of the total residue in each of the various edible commodities at any time between administration of the veterinary chemical product and depletion of the residues to permitted levels.

Maximum Residue Limit (MRL): the maximum concentration of a residue, resulting from the registered use of a veterinary chemical product, that is legally permitted or recognised as acceptable in or on human food of animal origin. The concentration is expressed in milligrams per kilogram of the commodity (or milligrams per litre in the case of a liquid commodity)”.

Method Limit of Quantification (LOQ): the smallest measured content of an analyte above which a determination of the analyte can be made with a specified degree of accuracy and precision.

MRL Standard: Maximum Residue Limits in Food and Animal Feedstuffs of Agricultural and Veterinary Chemicals and Associated Substances - available from Maximum Residue Limits on the APVMA website.

No-observable-(adverse)-effect-level (NO(A)EL): the highest concentration or amount of a substance, found in toxicology studies, to cause no detectable (usually adverse) alteration of morphology, functional capacity, growth, development or life span of the most sensitive test organism.

Residues of veterinary chemicals: all biologically active substances, whether active constituents, or degradation products and their metabolites which remain in foodstuffs obtained from animals to which the veterinary chemical product in question has been administered, or which have absorbed the veterinary chemical product via indirect administration eg in utero.

Target animal species: the species of food-producing animal(s) for which use of the veterinary chemical product is approved.

Target tissue: the edible tissue selected for monitoring and compliance testing of total residues in edible commodities from treated animals. When the concentration of marker residue(s) in the target tissue(s) complies with the relevant MRLs, the corresponding concentration of total residues in the daily food basket (as measured by the EDI) does not exceed the ADI.

Total residue: the total residue of a veterinary chemical in treated animals consists of parent compound, free metabolites, and metabolites that are covalently bound to endogenous molecules. The relative and absolute amounts of each residue component will vary among the tissues with the amount of veterinary chemical administered and the time following the last administration of the veterinary chemical. Total residues are typically determined in pharmacokinetics studies using veterinary chemical that has been radiolabelled with carbon-14.

United States Food and Drug Administration (USFDA) Center for Veterinary Medicine (CVM): the US agency that regulates the manufacture and distribution of food additives and drugs that will be given to animals, including food-producing animals. The CVM is responsible for ensuring that animal drugs and medicated feeds are safe and effective for their intended uses and that food from treated animals is safe for human consumption.

Withholding Period (WHP): the minimum period that needs to elapse between the last administration of the veterinary chemical product to an animal, and the slaughtering of the animal, or the collection of milk, eggs or honey from the animal for human consumption. The purpose of the withholding period is to ensure that edible commodities from treated animals contain residue levels below MRL.

7. REFERENCES and SUPPORTING DOCUMENTS

Details are provided for current editions at the time of publication. Applicants should always ensure that they obtain the most recent edition of any publication.

Acceptable Daily Intake (ADI) list (Acceptable Daily Intakes for Agricultural and Veterinary Chemicals). Therapeutic Goods Administration, Canberra. Available at http://www.health.gov.au/internet/main/publishing.nsf/content/ocs-adi-list.htm

Agricultural and Veterinary Chemicals Code Act 1994. APVMA, Canberra . Available from the APVMA website legislation page.

APVMA MRL Standard: Maximum Residue Limits in Food and Animal Feedstuffs. APVMA, Canberra . Available from the APVMA website MRL Standards page.

APVMA Residue Guidelines are available Available from the APVMA website MRL Standards page.

Commonwealth of Australia Agricultural and Veterinary Chemicals Gazette (APVMA Gazette). APVMA, Canberra . Available from the APVMA website Gazette page.

EMEA (CVMP) Note for Guidance: Approach towards harmonisation of withdrawal periods. Available at http://www.emea.eu.int/pdfs/vet/swp/003695en.pdf. Application software can be downloaded from http://www.emea.eu.int/index/indexv1.htm followed by clicking onto Guidance documents<>Safety<>Adopted Guidelines<> EMEA/CVMP/563/02.

EMEA (CVMP) Note for Guidance for the Determination of Withdrawal Periods for Milk. Available at http://www.emea.eu.int/pdfs/vet/swp/047398en.pdf. Application software can be downloaded from http://www.emea.eu.int/index/indexv1.htm followed by clicking onto Guidance documents<>Safety<>Adopted Guidelines<> EMEA/CVMP/231/00 (Rev1).

FAO Manual on the Submission and Evaluation of Pesticide Residues Data for the Estimation of Maximum Residue Levels in Food and Feed. FAO, Rome , 1997.

National Association of Testing Authorities (NATA) – Information on GLP recognition in Australia is available at www.nata.asn.au.

OECD Principles of Good Laboratory Practice (GLP) guidance document No. 1, available at the OECD’s website http://www.oecd.org/ehs/.

USFDA (Centre for Veterinary Medicine) Guideline for Establishing a Withdrawal Period. Available at http://www.fda.gov/cvm/Guidance/1732.htm.

FOOTNOTES

  1. Previously, estimates of chronic dietary exposure incorporated residue concentrations in foods at the level of the (proposed) MRL. However, given that the MRL is a single concentration representing the estimated upper limit of a high percentile of marker residue present in a given tissue of treated animals, the MRL is not considered to be a realistic indicator of the likely chronic exposure of consumers to residues over a lifetime. The median residue concentration represents the best point estimate of a central tendency over a prolonged period of time, because the concentrations of residues in a given tissue consumed varies from day to day, as reflected in the distribution. Further information may be located at http://www.who.int/ipcs/food/jecfa/summaries/summary66.pdf.
  2. Relevant scientific argument is defined as argument based on: accepted scientific principles; data published in peer reviewed journals; relevant texts; relevant case studies; or relevant clinical studies, where relevant means: related to the veterinary chemical or veterinary chemical product; or related to the claims and use patterns. Relevant scientific arguments must be accompanied by supporting documentation.
  3. For pigs, poultry and fish.
  4. The FAO Manual on the Submission and Evaluation of Pesticide Residues Data for the Estimation of Maximum Residue Levels in Food and Feed (FAO, Rome, 1997, p.40) states that when the log P value exceeds 4, the compound would generally be designated as fat-soluble.

REVISION HISTORY

Revision Date Description of Revision
1 July 2005

First edition

  • first MORAG edition - unchanged from the original Vet Requirements Series.
1 October 2005

Second edition

  • no changes.
1 June 2006

Third edition

  • complete revision of the content
1 July 2007

Fourth edition

  • minor layout changes