National Office of Animal Health
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Maximum Residue Limits (MRLs) and the Safety of Food from Animals

Residues of veterinary medicinal products, as defined by the European Union, are "pharmacologically active substances (whether active principles, excipients or degradation products) and their metabolites which remain in foodstuffs obtained from animals to which the veterinary medicinal product in question has been administered".

An MRL is the maximum concentration of residue following administration of a veterinary medicine which is legally permitted or acceptable in food under the laws of the EU.

The responsibility for keeping residues under the MRL lies with veterinary surgeons and farmers, using licensed animal medicines.

Use of animal medicines is strictly controlled by European law, and requires observance of the withdrawal period. This is the time which passes between the last dose given to the animal and the time when the level of residues in the tissues (muscle, liver, kidney, skin/fat) or products (milk, eggs, honey) is lower than or equal to the MRL. Until the withdrawal period has elapsed, the animal or its products must not be used for human consumption.

The withdrawal period is set out in the data sheet for the medicine and in the instructions for use which are part of the product packaging. Farmers are required by law to record all uses of animal medicines; it is therefore straightforward to ensure that withdrawal periods are observed.

Withdrawal periods exist so that MRLs are not exceeded and to ensure consumer safety. Accordingly, safety is of paramount importance when both MRLs and withdrawal periods are established and the legislators always err on the side of caution. As a result, although residues above the MRL should not occur, even if they do, they generally present no risk to the consumer because of the very large safety margins used in setting the MRL.

For example, the calculation of the MRL value is based on the acceptable daily intake (ADI; see below) for the drug in question. The calculation of the ADI includes an extremely large safety factor. In addition, the MRL calculation assumes an average intake per person of 500g of meat (over a pound!), 1.5 litres of milk (over 2.5 pints!), 2 eggs and 20g (nearly an ounce) of honey. Legislators might be well advised to consider the health implications for obesity and cholesterol levels!

Residues Surveillance

In the UK, farmers and veterinarians have an excellent track record of observing the regulations - and measures are in place to ensure things stay that way. As part of that effort, the Veterinary Medicines Directorate (VMD) operates two complementary surveillance programmes for residues of veterinary drugs in food of animal origin to ensure that residues above the MRL do not occur and that prohibited or illegal drugs are not being used:

Statutory Programme

A statutory programme fulfils the UK's obligations under Directive 96/23/EC. This Directive extended the previous statutory residues testing programme to poultry and aquaculture (salmon and trout), eggs, wild and farmed game and honey, and changed the previous regime for red meat by requiring a higher number of samples to be taken on farm with a consequent reduction in sampling at slaughterhouses.

Each year samples are collected from randomly selected farms and abattoirs by the State Veterinary Service (SVS) and the Meat Hygiene Service and analyses performed. In 2003 there were some 30 975 samples collected and 35 399 analyses performed. Analysis is carried out by the Laboratory of the Government Chemist and results are published by the Veterinary Medicines Directorate quarterly, and annually by the Veterinary Residues Committee (VRC). The results are presented for independent scrutiny at meetings of the VRC during the year. All the results are also seen by the Food Standards Agency. They can give a scientific opinion on the significance for human health.

In 2003 the VRC said that overall, the results of the National Surveillance Scheme indicate that the UK authorised uses of veterinary medicinal products did not result in residues of human health concern.

Follow-up action is taken by the State Veterinary Service on every sample which on confirmatory analysis shows the presence of unauthorised substances or concentrations of authorised substances above the MRL. A thorough on-farm investigation is carried out, with farmers advised how to avoid residues of veterinary medicines entering the food chain. If inspection of farm records and stock and the taking of further samples reveals clear evidence of abuse, the farmer will be prosecuted.

Non-Statutory Programme

A non-statutory programme supplements and complements the National Surveillance Scheme, extending residue analysis to imported and processed foods. It gives valuable information on foods that do not fall within the NSS.

Samples are taken from popular presentations of meat and animal products, collected from shops and at the border inspection posts. Samples are subjected to a range of analyses by the Central Science Laboratory in York. In 2003, there were 5468 analyses, targeted in particular foods where intelligence had suggested the possible presence of banned substances being used as veterinary medicines.

Retailers are informed by VMD of any "positive" samples purchased from their stores, and consumer organisations, local authorities, relevant trade associations and producers are contacted where appropriate to make them aware of the results.

If the products are imported, the SVS will contact the Chief Veterinary Officer of the country concerned. There are powers under the Food Safety Act to remove from the food chain food products containing residues at concentrations which represent a danger to human health.

In addition to these schemes, milk is tested for antibiotic residues by the dairy companies and heavy penalties face dairy farmers whose milk fails to meet the necessary requirements. Food retailers and processors also frequently carry out their own checks.

How MRLs are set

Maximum Residue Limits are set by the European Commission after adoption by the Standing Committee, following an opinion of the Committee for Veterinary Medicinal Products (CVMP). Manufacturers apply for an MRL, supplying the CVMP with two dossiers of information - on safety and residues - from which they can make their assessment.

The Safety Dossier contains all the pharmacology and toxicology studies carried out with the medicine in laboratory animals.

These studies examine what happens to the substance in the body and assess how much can be given safely, without inducing any unwanted adverse effects.

The safety dossier also includes the calculation of the ADI referred to earlier. This is based on results in laboratory animals and particularly on the so-called No-Observed-Effect Level (NOEL), the dose with no observable effect in the most sensitive test used.

The World Health Organisation recommends that once the NOEL has been determined, a safety factor of between 100 and 1000 (usually depending on the type of effect) is applied to derive the ADI.

The Residues Dossier contains all the data concerning the formation, nature, behaviour and disappearance of residues after a medicine has been given to a farm animal.

Together, the results from the residues file on the quantities and behaviour of residues in farm animals, with the ADI derived from the safety file and the theoretical food intakes mentioned earlier (500 g meat, 1.5 litres of milk etc) are used to calculate the MRL(s), on the assumption that consumers get the maximum level every day of their lives.

Determining MRLs is a requirement of European legislation under a Council Regulation (2377/90). Under this legislation, substances must be entered into one of four annexes to the Regulation:

Annex I: Final MRLs

The data in the dossier are considered adequate to establish a final MRL.

Annex II: MRLs not necessary

The data in the dossier demonstrate that there is no risk to the consumer and MRLs are not needed.

Annex III: Provisional MRLs

This is for medicines where MRLs can be established but some clarification of further studies are required before final MRLs can be set.

Annex IV

Residues of the the medicine pose an unacceptable risk to the consumer or there is insufficient information to allow a full assessment. The products in Annex IV are prohibited for use in food producing animals in the European Union.

No new medicine can be licensed or sold for use in food producing animals until its active ingredients have been entered into Annexes I, II or III of the Regulation.


Considerable research effort is put into developing the safety and residues dossiers for veterinary medicines so that the ADI values can be calculated, MRLs set and withdrawal periods established. This process, together with residues monitoring to ensure that residues above the MRL do not occur and that prohibited drugs are not used serves to ensure safety for the consumer, especially as large safety factors are built in at several stages of the process.

Violations of MRLs or the uses of prohibited substances, detected under the surveillance programme, are investigated and, where appropriate, are prosecuted. Legal sanctions can be taken against individuals who ignore instructions on the proper use of products.

Further reading:

The Veterinary Residues Committee Annual Report on Surveillance for Veterinary Residues in 2003 (

Animal Medicines Record Book (available from NOAH)

NOAH press release "NOAH Responds to Organic Lobby Report" (5 June 2001)




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