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A new decision tree for veterinarians

The latest tool for fighting antibiotic resistance

A new decision tree for veterinarians

Very recently the Canadian Veterinary Medical Association along with several partners came up with a Therapeutic Decision Cascade for Animal and Public Safety. This is a great tool for reminding all of us how to properly select drugs for any species we are treating. By considering that all we want is to look after the health of our patients and that what we do ultimately affects human health, this guide is invaluable to both veterinarians and their clients as a reminder of which medications are approved for each species.

We are fortunate in the cattle industry in that we have many products approved for cattle. To be approved means a product has a known withdrawal time for meat and milk (if used in dairy cattle). They also come with a DIN or drug identification number. It would be very rare indeed for a large-animal veterinarian to use products not approved for use on bovines, and if they did it would be done under a written prescription.

We need to use these products prudently. That means we only use Category 1 drugs such as Baytril, Excede or Excenel for treatment, and for specific conditions at that.

As veterinarians we also need to do more cultures and sensitivity tests on behalf of our clients to determine which antimicrobial is in fact the best for a particular condition such as respiratory disease.

Many more prescriptions are written for minor species such as sheep and goats as these products have not been fully researched in these species. Primarily this is necessary because the amount of sales with these species would not justify the regulatory or research cost to put them on the label.

We call this extra-label usage which covers approved products for other species or products given in a different route or with a higher dosage than indicated. Your veterinarian will use the best resources at hand such as Canadian CgFARAD (Global Food Animal Residue Avoidance Databank) which is a national food safety database that can give us recommendations on extra-label usage for withdrawals, safety etc. Technical services veterinarians are also approached from the various pharma companies for their expertise on the products they handle. We need to consider safety first because as veterinarians we first want to do no harm.

The third category in this cascade is using an approved human drug. Although this is very rare in cattle practice it is more common in equine or small-animal practice. Again this is done by prescription and only after veterinary-approved drugs are first considered. This usually occurs when certain infections have proved resistant to our veterinary drugs after a culture has been done.

The last three categories are what we call compounded drugs. One group is made from other veterinary-approved drugs for say a different method of administration. The others are drugs compounded from human drugs. The most critical, and probably overused and overabused, are drugs made from the raw products. These are called active pharmaceutical ingredients (API) and are imported as raw product from other countries and because there is not near the control on their manufacture the CgFARAD cannot comment on their safety.

In production animal beef practice we have the ability most times to stick with an approved product because most new products are approved for cattle when licensed. We mostly pick from the top and with producers knowing about this decision tree if the need comes to use a compounded product one can stress to your veterinarian to use the API category as a last resort. This is one loophole in our import regulations that the government may try and close as these products have no DIN in this country and the potential for abuse and exceeding drug withdrawals is huge.

The provincial associations will start possibly creating a document for best-use practices for extra-label usage on minor species that can serve as a very good guide to your herd’s veterinarian.

The approved veterinary drugs fall into four categories themselves ranging from Category 1 being those of high importance in human medicine to Category 4 which covers the ionophores which have low importance in human medicine. Most of the antimicrobials used in production animal medicine are Categories 4, 3 and 2.

Alberta Beef Producers ( is putting out an excellent brochure on this topic that illustrates the various categories beautifully with several examples. It also discusses some of the other things the cattle industry is doing to tackle this antimicrobial-resistance issue. Watch for it. It will be useful if you want to ever explain antibiotic resistance as it relates to animals to your urban family, friends or neighbours.

Remember, when a product is called for the decision tree that your veterinarian will work through to decide which drug to prescribe is Approved Vet Product > Extra Label Drug Usage > Approved Human Drug > Compounded Products. In other words, it’s veterinary first, then human and finally API.

We in the cattle industry are in a position to be leaders for the other species because we have so many products approved for use, and by staying away from the Category 1 products as much as possible.

For more guidance on this topic talk to your herd veterinarian when antimicrobial decisions are made.

Click here for the Health Canada website detailing the drugs in each category.

About the author


Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.



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