Setting Standards for Maximum Residue Limits (MRLs) of Veterinary Drugs Used in Food-Producing Animals

For Your Information:

Health Canada's mandate is to maintain and improve the health of Canadians. Health Canada's Veterinary Drugs Directorate (VDD) is responsible for ensuring the safety of food produced in Canada from food-producing animals. To accomplish this, VDD conducts comprehensive scientific reviews of veterinary drugs before they are approved for sale in this country.

Every substance, whether a vitamin or a drug, whether natural or synthetic, is toxic at certain levels - the dose differentiates between a poison and a remedy. This is why human or veterinary drugs are beneficial at recommended dosages but could be harmful if such dosages are exceeded.

What is a Maximum Residue Limit?

A Maximum Residue Limit is an amount of residue that could remain in the tissue or food product derived from a food-producing animal that has been treated with a veterinary drug. This residue is considered to pose no adverse health effects if ingested daily by humans over a lifetime. MRLs are established only after VDD has conducted extensive reviews of data submitted by manufacturers and has determined that foods containing these veterinary drugs residues up to the recommended levels, are safe for human consumption.

Who determines the potential risk to Canadians of dietary exposure to veterinary drugs?

Dietary exposure to veterinary drugs occurs when residues remain in food products derived from animals treated with a veterinary drug.

Health Canada establishes maximum residue limits that are safe for human consumption by using a scientific, multi-step, health risk assessment process that is internationally recognized.

When a potential health risk is identified in foods in the marketplace, Health Canada, through VDD is called upon to assess the risk to Canadians. The Canadian Food Inspection Agency (CFIA) is authorized under the Food and Drugs Act to take corrective action if warranted.

Recent technological advancements have enabled scientists to improve methods that can detect minute amounts of residue that could remain in foods.

How does Health Canada's multi-step health risk assessment process work?

Health risk assessments of veterinary drugs used for food-producing animals are carried out using the best available data and highest possible standards.

This process has six key steps:

• Studies on veterinary drugs in living organisms (metabolism studies) conducted in the food-producing animal (e.g., swine, chickens, cows, etc.) are reviewed to determine the amounts and length of time it takes for a drug and its transformation products (metabolites) to be excreted.
• Comparative metabolism studies conducted in laboratory test animals are also reviewed to ensure that similar patterns of metabolism exist in these animals.
• Toxicity of the substance is determined by toxicity/carcinogenicity (cancer) testing. This is based on the knowledge that the dose makes the poison. This information allows VDD scientists to determine the safe quantity of substances that humans can consume each day for a lifetime, without any threat to their health. This quantity is called the Acceptable Daily Intake (ADI).
• In the next step, the safe concentration for Total Residue Levels (TRLs) are established by ensuring that consumption of edible tissues, for example, muscle, liver, kidney and fat or food products such as milk, eggs and honey do not exceed the Acceptable Daily Intake. An MRL is then set for the concentration of the drug residue remaining in the tissue sample. This is called marker residue and is used to monitor the Total Residue Levels which are considered to be safe for human consumption.
• The analytical methodology developed for the marker residue in food is evaluated.
• A withdrawal period is then established based on the residue depletion data for the marker residue in the tissue, or withholding time for other food products such as milk.

The labels for the respective veterinary drug product must include WARNING statements. These include withdrawal periods (WPs) for tissues or withholding times (WTs) for milk, when applicable, restrictions of use, and warnings for the handler of the drug.

How long does it take a manufacturer to demonstrate the safety, effectiveness and quality of a new product?

It may take years for a manufacturer to do the work required to develop sufficient information to demonstrate the safety, effectiveness and quality of a new product. Products are evaluated thoroughly before they can be sold or used in Canada. Manufacturers must submit very detailed scientific data to show that their product can be used safely, and that it meets all of the criteria for acceptability prescribed by regulations.

Following the approval of products, the CFIA undertakes monitoring and compliance activities to make sure that MRLs are adhered to. In addition, targeted research is underway at Health Canada to ensure the continued safety of our food supply. For example, veterinary drugs are part of national monitoring studies which provide data on the exposure of Canadians to a variety of substances. Regulatory scientists work closely with researchers in the planning of these studies, and in other areas of research and monitoring related to chemical and microbiological substances and food safety.

Once the evaluation of a drug is complete, the proposed MRL must go through a consultative review with our stakeholders. The proposed MRL then goes through the regulatory process before it can be promulgated into the Food and Drugs Act and Regulations.

Why does VDD not use MRLs already established by other regulatory bodies?

VDD bases veterinary drug marketing, labelling and the establishment of MRLs in Canada on scientific assessments that take into consideration scientific views from other jurisdictions. Canada's drug approval system, animal husbandry practices and legislation vary from that of other countries. Consumption patterns also vary according to cultural practices in different countries. Therefore, while efforts are made to harmonize when possible, their conclusions may result in establishing different MRLs for veterinary drugs.

The health of Canadians is of paramount importance to Health Canada. The Veterinary Drugs Directorate works to ensure the safety of Canada's food supply and that veterinary drugs sold in Canada are safe and effective for animals.

Applicable Act: Food and Drugs Act

For more information:
You can visit our Web site and read more about the progress made on this issue http://www.hc-sc.gc.ca

Veterinary Drugs Directorate
Health Products and Food Branch

Health Canada
Holland Cross Complex
Ground Floor
14 - 11 Holland Avenue
Ottawa, Ontario
K1A 0K9
Address Locator - 3000A

General Information Number:
(613) 954-5687
Fax: (613) 957-3861

Links:

Maximum Residue Limits Information - December 2002