The Canadian Veterinary Medical Association and several partners have come up with a therapeutic decision cascade for animal and public safety.
This is a great tool for reminding veterinarians and producers how to properly select drugs for any species we are treating.
The guide is invaluable as a reminder of which medications are approved for each species. That is important because the products used to treat farm animals and pets ultimately could affect humans.
The cattle industry has many products approved for use. To be approved means a product has a known withdrawal time for meat and milk (if used in dairy cattle). An approved product comes with a drug identification number (DIN).
It would be rare for large animal veterinarians to use products not approved for use on bovines, and if they did it would be done under a written prescription.
When we use antibiotic products, we must do so prudently. That means using only Category 1 drugs. Drugs of very high importance to human health, such as Baytril, Excede and Excenel, should be used only for treatment and only for specific conditions.
Veterinarians also need to do more cultures and sensitivity tests to determine which antimicrobial is the best for a particular condition such as respiratory disease. This means we may initiate treatment first and then change antibiotics if cultures show a better choice.
Veterinarians who treat minor species such as sheep and goats have to write more specific prescriptions because far fewer products have been researched for them. The amount of product sales for these species would not justify the regulatory or research cost to put them on the label.
Your veterinarian must determine which product is safe and effective to use.
This is the second level in the cascade. 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 on the label.
Your veterinarian will use the best resources at hand, such as a national food safety database called CgFARAD, which can provide recommendations on extra-label use for such things as withdrawals and safety.
Technical services veterinarians from pharmaceutical companies are also approached for their expertise on the products they handle.
The third level in the cascade is using an approved human drug. This is rare in cattle practice but is more common in equine or small animal practice.
It is done only by prescription and only after veterinary approved drugs are first considered. This usually occurs when certain infections have proved resistant to veterinary drugs after a culture has been done.
The last three levels in the cascade are what are called compounded drugs. One group is made from other veterinary approved drugs, which might have a different method of administration. The other group is drugs compounded from human drugs.
The most critical, and probably overused and over-abused, are drugs made from raw products. These are called active pharmaceutical ingredients (API) and are imported as raw products from other countries.
There is much less control on their manufacture, so the CgFARAD cannot comment on their safety. This method should be used only as a last resort.
Beef cattle veterinarians can usually stick with an approved product. Most new products are ap-proved for cattle when licensed.
The API category is a loophole in our import regulations that the government may close. These products have no DIN in this country, and the potential for abuse and exceeding drug withdrawals is huge.
Provincial associations may start creating a document for best use practices for extra-label use for minor species that can serve as a good guide to your herd’s veterinary practitioner.
Approved veterinary drugs that are antimicrobial fall into four categories ranging from Category 1 — those of high importance in human medicine — to Category 4 — low importance in human medicine, which covers the ionophores. Most of the antimicrobials used in production animal medicine are categories 4, 3 and 2.
Alberta Beef Producers has a brochure on this topic called Worried about antibiotic use and resistance in cattle? The brochure, which is on ABP’s website, illustrates the four antibiotic categories beautifully with several examples.
It also discusses additional things the cattle industry are doing to tackle antimicrobial resistance.
One pharmaceutical company has a chart listing the common antibiotics and the category they fall into. It is great to hang on your wall. This material will be useful if you want to explain antibiotic resistance as it relates to animals to your urban family members, friends and neighbours.
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. Stay away from the human medicine Category 1 products as much as possible.
For more guidance on this topic, talk to your herd veterinarian when antimicrobial decisions are made or treatment protocols written.
As well, Health Canada has a website detailing the drugs in each category at www.hc-sc.gc.ca/dhp-mps/vet/antimicrob/amr_ram_hum-med-rev-eng.php.
Roy Lewis works as a technical services veterinarian part time with Merck Animal Health in Alberta.