Keeping and eye on food supply.
"First", explains Sved, "let us consider how drugs, which are used in animals destined to become our food, should become a concern in our plates. Animals, like humans, are sometimes sick; and like humans, they are treated with drugs. Most of what goes in eventually comes out, but it does take time. Before the drug is eliminated, the normal metabolic processes of the animal can also convert the original drug to forms that are toxic. If the elimination time is misjudged, we have residues, consisting of the drug itself or some of its toxic break-down products, remaining in the animal at the time of sale.
Another source of residues may be treatment of animals to prevent disease. Growing animals may be given antimicrobials or antibiotics to prevent dysentery, paratyphoid, coccidiosis or other infectious diseases. Hence the source of residues. Low levels of antibiotics and hormone-like drugs are also given to promote growth (so the farmer can raise animals at a cost the consumer is willing to pay), and are a third possible source of residues."
Drugs most commonly administered to animals are penicillins, sulfas, tetracyclines or nitrofurans. These are also given to humans at therapeutic doses, so where is the hazard at the very low concentrations encountered with residues in food (parts per million to parts per billion)? For most of the population there probably is none, but for the 10% or less who are allergic to any of these drugs there are dangers. The possibility of carcinogenicity of metabolites even at very low concentrations also cannot be discounted. Bacteria may sometimes develop resistant strains when exposed to residue levels of drugs, and if the bacteria are pathogenic to humans, treatment becomes difficult. Another indirect problem is interference with industrial processes, such as cheese making, from milk containing drug residues. Fermentation is greatly delayed, causing poor quality of cheese, and added expense of production, an eventual concern to the consumer.
How can the risk of residues in our food be reduced? This concern of the Drug Residues Section can be considered in two ways: post-market surveillance of the drugs in foods, and pre-market evaluation of the drugs themselves.
Once the drug is on the market, surveillance of meat, milk or eggs is usually done by Agriculture Canada or provincial government organizations. However, the Section develops and verifies new and more sensitive analytical methodology for the use of these organizations. The methods are of three main types: chemical analyses are being developed and evaluated by G. Carignan, K. Carrier and A.I. MacIntosh; immunoassays or microbial assays are the domain of Mrs. L. Larocque. There are various reasons why new and more sensitive methods may be needed for old drugs on the market for some years. New uses may be approved for the drugs, and methods are needed to determine residue levels, under these new conditions. New research may indicate a drug, once considered harmless, does have toxic effects, and lower tolerances may be put into effect. A drug may be banned for use in food-producing animals, but remain on the market for treating pets, horses, etc. Illegal use of these has to be detected and discouraged.
The Drug Residues Section is also involved in pre-market evaluation of drugs. Evaluation of claims made by manufacturers when applying for approval to market their products may be done in the laboratories to help the Bureau of Veterinary Drugs to evaluate the submission. Research on drug metabolism may be conducted to help determine the nature of the break-down products and the time required for elimination of residues and metabolites.
Another problem which sometimes requires help from the section is identification of unknowns which are found in routine survey work by other organizations. A recent example was the identification of a break-down product of vitamins in swine feed which had separation characteristics similar to tetracyclines. MacIntosh worked in close cooperation with other divisions of the Bureau to identify the material, which was recognized to be no hazard to humans.
A.I. MacIntosh and G. Carignan also collaborate in performing animal experiments to measure residue levels in food under simulated farm conditions, rate of accumulation and elimination of the drug under laboratory conditions, or to study the formation of metabolites of human health concern.
The human drugs part of the the Drug Residues Section under J.C.K. Loo with N. Beaudoin, is concerned with the presence of drugs in the blood of patients under treatment. Loo is establishing the absorption and elimination characteristics of steroid hormones and drugs used in asthma and organ transplant, and the formation and identification of metabolic products which may contribute to the toxic side effects of these drugs.
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|Title Annotation:||Canada's Bureau of Drug Research|
|Author:||Sved, Stephen; MacIntosh, A.I.|
|Publication:||Canadian Chemical News|
|Date:||Nov 1, 1989|
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