Maximum Residue Limits (MRLs)
Frequently Asked Questions

Questions

1. What is a Maximum Residue Limit (MRL)?
   
2. What is an Administrative Maximum Residue Limit (AMRL)?
   
3. Why might Canada have some different MRLs than the tolerances that are established by the US or other jurisdictions?
   
4. Where are Canadian MRLs published?
   
5. Why are there not MRLs for all veterinary drugs?
   
6. What about carbadox?
   
7. If I am taking a prescription drug such as an antibiotic, how do I know that I am not getting too much if I am eating food products that may contain residues of this same drug?
   

Answers

1. What is a Maximum Residue Limit (MRL)?

A Maximum Residue Limit (MRL) 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.

2. What is an Administrative Maximum Residue Limit (AMRL)?

An Administrative Maximum Residue Limit (AMRL) is derived by following the same scientific process used to establish an MRL. The only difference is that, in the case of an AMRL, the regulatory process to publish this information is in progress. Once the regulatory process is complete the AMRL is known as an MRL.

MRLs and AMRLs are established only after Health Canada's Veterinary Drugs Directorate (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.

3. Why might Canada have some different MRLs than the tolerances that are established by the US or other jurisdictions?

Maximum Residue Limits are established by regulatory agencies for purposes of monitoring of residues of chemicals (veterinary drugs, pesticides, inorganic chemicals, etc.) in food. In the US, they are called tolerances and are established by the US Food and Drug Administration's (FDA's) Center for Veterinary for Veterinary Medicine (CVM).

While efforts are made to harmonize, our respective conclusions may sometimes result in establishing different MRLs or tolerances for veterinary drugs. In Canada, VDD bases veterinary drug marketing, labelling and the establishment of MRLs on scientific assessments that take into consideration scientific views from other jurisdictions. Canada's drug approval system, animal husbandry practices (care and management) and legislation varies from that of other countries, including the US. Food consumption patterns also vary according to cultural practices in different countries. There also may be differences in the methodology used to measure residues or in the way that the MRLs (tolerances) are calculated.

The health of Canadians is of paramount importance to Health Canada. VDD works to ensure the safety of foods derived from food-producing animals treated with veterinary drugs and that veterinary drugs sold in Canada are safe and effective for animals.

4. Where are Canadian MRLs published?

Once the evaluation of a veterinary drug is complete, stakeholders are consulted and have the opportunity to provide feedback on the proposed MRL. The proposed MRL then goes through the regulatory process before it can be published in the Food and Drugs Act and Regulations.

Since it can take many years before an established MRL is published in the Food and Drugs Act and Regulations, VDD has developed a table of approved MRLs and AMRLs www.hc-sc.gc.ca/dhp-mps/mrl-lmr/mrl_comparisonnew_e.html
This table is updated as new MRLs and AMRLs are established.

5. Why are there not MRLs for all veterinary drugs?

There are two possibilities why MRLs are not established for some veterinary drugs for food-producing animals. Either there is no approval given for that particular species in Canada or the regulatory process to establish a particular MRL has not been initiated. In both cases, no detectable residues are permitted.

6. What about carbadox?

On August 10, 2001, Health Canada issued a Stop Sale Order for carbadox. Carbadox is an antimicrobial product that was approved for sale in Canada in the 1970s to prevent and treat disease in swine and to maintain weight gain during periods of stress, such as weaning. Health Canada's decision to issue a Stop Sale Order was based on a better understanding of the science, risk factors, knowledge of misuses of the product, and the difficulty in controlling the use of this drug according to label directions.

Carbadox remains in use in the US, but is banned in other countries (Australia and the European Union). Recently, at the February 2003 Joint WHO/FAO Expert Committee on Food Additives (JEFCA) meeting, the Committee recommended the withdrawal of MRLs for carbadox.

7. If I am taking a prescription drug such as an antibiotic, how do I know that I am not getting too much if I am eating food products that may contain residues of this same drug?

Prescriptions are given under the care of a doctor and maximum daily dosages are carefully prescribed. In addition, prescription drugs are taken over a short period of time (usually ten days to two weeks). VDD scientists establish MRLs in food and milk based on a complex formula to determine the safe quantity of substances that humans can consume each day over a lifetime and, compared to human therapeutic doses, represent extremely low quantities.