Prescriptions for Man, and Man's Best Friend
Veterinary pharmacy is a difficult field. Pharmacists must judge if the prescribed dose is appropriate for the pet, based upon age, gender, species, and indication.
Even though humans, dogs, cats, cows, and alpacas are all mammals, when it comes to disease diagnosis, progression, and treatment, the similarities diminish, and differences present themselves.
In human medicine, physicians complete dedicated training programs lasting more than 8 years to be able to accurately diagnose, and appropriately treat patients. Pharmacists spend 6 years mastering dosing, pharmacology, and the intricacies of each medication used to treat human problems. In animal medicine, veterinarians are schooled for 8 years, and spend little time learning pharmacology.
Veterinarians simply do not have time in their curriculum to have extensive pharmacology training. Veterinary students take 2 pharmacology courses in their second year, and a toxicology course to cover adverse reactions, and other drug-related issues. After about 2.5 years in the classroom, they spend the remaining time completing clinical training.
The biggest difference between human and veterinary medicine is that veterinarians treat many different species, whereas medical doctors deal with only 1. Veterinarians spend an entire year learning about different 'normal' anatomies, and physiologies, compared to medical students who take a course or 2 learning human anatomy, and physiology.
Veterinary pharmacy is a difficult field. Community pharmacists need to know a bit about veterinary pharmacy because pet owners often bring pet prescriptions to local pharmacies. Pharmacists must judge if the prescribed dose is appropriate for the pet, based upon age, gender, species, and indication.
Below are some tips to guide pharmacists about pet prescriptions:
1. Do not recommend any over the counter (OTC) medications to pet owners. Pets cannot ingest OTC NSAID’s (ibuprofen and naproxen) or acetaminophen. A few OTCs, like famotidine, diphenhydramine, and dimenhydrinate, are safe. Always check dosing by consulting a veterinarian guide, such as Plumb’s Veterinary Drug Handbook.
2. Veterinarians may recommend vitamin supplements, like glucosamine with chondroitin, for pets with symptomatic arthritis. Pet owners may come to the pharmacy in search of this product, and some veterinarians indicate any generic is fine. Remember: the FDA does not regulate OTC supplements for human use, so safety data is unavailable in humans, and animals. This is important for consumers to know. Veterinarians will often recommend brands designed specifically for animals, e.g., Dasuquin (contains avocado/soybean unsaponifiables) or Cosequins. These formulations come as chews that most dogs like, and have few side effects.
3. Xylitol is extremely toxic to dogs. This toxicity has been documented at 50 mg/pound of body weight. A naturally occurring substance, xylitol is a common sugar substitute. With a fraction of regular sugar's calories, it has a low glycemic index. It is found in many OTC products, including, but not limited to, cough syrups, digestive aids, vitamins, supplements, and allergy medicines. Even low doses can cause hypoglycemia, liver failure, and seizures. The Pet Poison Helpline (1-800-213-6680) reports accidental gum ingestion as the most common source. Most pieces of gum contain 1 gram, so only 9 pieces are toxic to most dogs, and will lower blood sugar. The more xylitol ingested, the higher the risk of liver failure. Advise pet owners to call the Pet Poison Helpline if a dog ingests xylitol. Checking all product labels when looking for a dog-safe product is crucial.
4) Metronidazole is an antifungal used for common GI or gut infections. In canines, veterinarians prescribe it for giardia, anaerobic infections, and inflammatory bowel disease presenting as diarrhea. This medication's dosing varies by species because their drug metabolisms differ. For example, dogs with giardia need metronidazole at a dose of 25-65 mg/kg/day PO for 4 days, but cats need 25 mg/kg every 12 hours for 8 days. (This highlights an important clinical pearl: felines cannot be treated as 'small dogs.') Regardless of species, most pets find metronidazole's taste unpleasant. Animals may salivate heavily if the drug is in contact with mucous membranes for too long; advise owners not to crush this medication for their pets. To avoid GI side effects, give this medication with food.
5) Pharmacists should be aware of the high dose of levothyroxine required for canine hypothyroidism, due to its short half-life and absorption variability. Levothyroxine is usually prescribed once daily at doses lower than 200 mcg in humans. In dogs, a dose of 0.02 mg/kg twice daily is recommended, up to a maximum of 0.8 mg twice daily. Generally, owners will start to see improved alertness and activity within a week or two of initiating the medication. Other improvements, such as a glossier hair coat, and increasing body weight, can be seen within 4 to 6 weeks.
'Human medicine' pharmacists can’t possibly be expected to know everything about medication administration in animals. The University of Florida has several courses available online. In addition, Plumb’s Veterinary Manual is available for purchase on Amazon for about $80. Pharmacists should contact the veterinarian's office with questions about prescriptions or discrepancies (medication, dose, quantity, formulation available, etc.).
This is the key point to remember: Each species may metabolize medication differently, and most doses are weight based. Consider developing a relationship with a local veterinarian’s office for questions that might arise.
Alexandra Coults is a 2018 PharmD Candidate at the University of Connecticut.