A CCWHC Technical Bulletin:
Drug Residues in Wild Meat – Addressing A Public Health Concern
Veterinary drugs play a valuable role in wildlife management and research. They are used
widely for a variety of reasons, in particular, the capture and restraint of wild animals (Table 1). However, the availability and use of veterinary drugs is threatened if government regulations or thepublic trust are violated.
Drug residues in wildlife are an important public health concern, especially for those who
consume wild meat. Although the likelihood of consuming meat from a wild animal administered drugshortly before death is small, wildlife personnel (conservation officers, park wardens, biologists,veterinarians, etc.) are still confronted from time to time with the question, “Is the meat of a druggedanimal safe to eat?” And, because data regarding the safety of drug residues and their rates ofclearance from the tissues of wild animals are few, answers can sometimes seem uncertain. As aconsequence, credibility may be weakened and the public left wondering.
Table 1. Types of drugs used for wildlife management and research.
1. For capture, restraint, and reversal
2. For disease conditions and injury
To prevent or treat infection by parasitic
Concern about drug residues extends also to food products derived from domestic livestock.
Here, the concern is addressed, in part, by producers waiting for a specified time before slaughter oruse of products like milk. This period, called the drug withdrawal time, is established for many drugsand is defined as the interval from when an animal is last given a drug to when it is considered safe forhuman consumption. The approval of new veterinary drugs, including determination of drug withdrawaltimes, is an expensive and lengthy process that involves research, development, and validation of newdrugs for safety and effectiveness by drug companies, and a comprehensive scientific review of druginformation by Health Canada’s Veterinary Drug Directorate. For this reason, drug companies areunwilling to invest money and time to determine a drug withdrawal time for a product unless the market
for the drug is big enough to justify the expenditures.
The application of veterinary drugs to wildlife management is a limited market, in many cases
too small to justify investment by drug companies. As a consequence, many of the drugs used bywildlife personnel were developed for use in domestic animals or humans, and the application to wildlifeis carried out in an “extra-label” manner. Extra-label use is defined as the use of a drug product in amanner that is not consistent with uses indicated on the label (package insert or product monograph) ofany drug product approved by Health Canada, or the use of a drug product that has never beenapproved by a regulatory authority in this country, e.g. Telazol®. Extra-label use is practised by avariety of people, including pharmacists, health technicians, feedlot managers, animal breeders,veterinarians, and wildlife personnel. The basis for extra-label use is reasonable extrapolations fromdrug safety and efficacy information established for other species, mostly domestic animals or humans.
Wildlife personnel have two options to answering the question, “Is the meat of a drugged wild
animal safe to eat?” One is to conduct research into the safety of drug residues and their rates of
clearance from the tissues of wild animals. The other is to extrapolate from established information for
other species. Drug research with wild animals is limited by many uncontrollable factors, including
variability in dosing levels, injection sites, and sampling times, and the small number of animals that can
be killed for tissue collections. As a result, years of painstaking research can result in insufficient
information to determine a drug withdrawal time. As an example, Telazol® is a veterinary drug that has
not been approved for routine use by Health Canada, but nonetheless it is used by many as the drug-of-
choice for the immobilization of polar, black, and grizzly bears in Canada. In the early 90’s, three years
of research was conducted to determine how long drug residues are likely to remain in tissues and fluids
of polar bears after immobilization with Telazol®.1 The investigators concluded that residues were
quickly cleared from most tissues, and from these results it would be highly unlikely that a human
consuming polar bear meat from an animal killed more than 24 hr after immobilization would experience
any effect of the drug. Nevertheless, Health Canada decided that polar bear meat should not be
consumed by humans for one year following immobilization, and that this long withdrawal period would
remain in effect until more definitive toxicological and residue clearance studies could be conducted to
support a shorter withdrawal period.2 More recently, Health Canada has extended the one-year
withdrawal for Telazol® to apply to all species and acquisition of this drug is not possible without first
signing and dating the following statement: “Treated animals must be identified with tags to
indicate the date of treatment and they must not be used in food for human consumption for at
least one year (12 months) following the latest treatment with this drug.”
of drug withdrawal times based on established information for other species is the more practical
Suggested withdrawal times for many of the drugs used in free-ranging wildlife in North
America were determined by the Western Wildlife Health Committee of the Western Association ofFish and Wildlife Agencies in the mid-90’s, and have since been adopted by many provincial, territorial,and state wildlife agencies (Table 2). Comparison with established times for captive or domesticanimals indicates that conservative withdrawal times have been suggested for wildlife to prevent theoccurrence of adverse reactions in humans consuming meat containing drug residues.
Table 2. “Suggested” withdrawal times for drugs used in free-ranging wildlife in comparison to “established”withdrawal times for the same drugs when used in captive red deer in New Zealand, and in domestic livestock inNorth America.
Withdrawal Time (days) Following Intramuscular Injection
Free-Ranging WildlifeA Captive Red DeerB Domestic LivestockC
(Aceprom, Atravet, Notensil,
(Acarexx, Heartgard 30, Ivomec)Ketamine
(Anaket, Ketalean, Ketaset,
(Trexan, Trexonil)Penicillin (long-acting)
(Anised, Cervizine, Cervizine 300,
Rompun, Sedazine, Tranquived)Yohimbine
(Antagonil, Yobine)Zolazepam and Tiletamine (1:1)
A Withdrawal times as suggested by the Western Wildlife Health Committee of the Western Association of Fish and
B Withdrawal times as established by the Ministry of Agriculture and Fisheries New Zealand.
C Withdrawal times as established by either Health Canada’s Veterinary Drugs Directorate or the Food Animal
Residue Avoidance Databank (FARAD) in the United States.
Because many of the wild animals administered veterinary drugs are potential food-producing
animals (e.g., deer, elk, bear), it is essential that they are identified clearly by some sort of durableexternal marker, e.g., ear tag, neck collar. Further, the marker should display a unique number and anappropriate notification warning (e.g., NOTICE: Call “this phone number” prior to consumption) thatrefers the hunter to the agency responsible for administering the drug. Provided that agencies enforcestrict guidelines on recording and cataloguing all drug administration information, wildlife personnelshould be able to address with some degree of confidence questions regarding the safety of consumingmeat from an animal killed after it was administered veterinary drugs. Animals killed within the drugwithdrawal period should be condemned as unfit for consumption, and animals killed outside this rangeshould pose no risk of any adverse drug effect.
References: 1. Semple, H.A. et al. 2000. Pharmacokinetics and tissue residues of Telazol® in free-ranging polarbears. J Wildl Dis 36: 653-662. 2. Calvert W. 1998. Research on polar bears in Canada 1993-1996. Proc 12th WorkingMeeting of the IUCN/SSC Polar Bear Specialist Group. Occasional Paper of the IUCN/SSC No. 19. pp. 69-91.
(Marc Cattet, CCWHC Western/Northern Region).
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