Finding out more about prescribing in companion-animal practice

Finding out more about prescribing in companion-animal practice

Since working on the module on metronidazole neurotoxicity I have been interested in finding out more about how metronidazole is used in veterinary practice (what for, at what doses and for how long) particularly because in the meantime there has been a new publication reporting a series of cases of neurotoxicity in dogs (Tauro et al 2018).

So far I have found very little that is helpful. This has made me wonder about what is known more generally about the use of veterinary medicines in practice. Although we get some information about the efficacy (benefits) of medicines from formal clinical trials, particularly those done to gain a marketing authorisation for a medicine, these are limited by being conducted on relatively small numbers of animals from tightly-defined populations. We also get information about the harms of medicines from the pharmacovigilance system run by the Veterinary Medicines Directorate; this relies on voluntary reporting and is thought to suffer from under-reporting. And information about the amounts of medicines sold is held by pharmaceutical companies and wholesalers. But little is know about how medicines are used in practice and the benefits and harms they bring.

During my search I came across an interesting report from the researchers at the Small Animal Surveillance Network (SAVSNET) that sheds some new light on prescribing practices (Singleton et al 2018). The researchers looked at electronic health-record data collected during booked consultations in 457 UK-based companion animal veterinary practices over a 2-year period. (2014–2016). 

In the 2 years, at least one prescription was recorded in 65% of consultations involving dogs; 69% involving cats; 56% involving rabbits. In all, 81% of dogs and cats and 68% of rabbits were prescribed at least one medicine. Vaccines were the most commonly prescribed family of medicine in all species (dogs 28%; cats 30%; rabbits 22%). Rabbits were euthanized more frequently (4% vs. 2% of dog consultations; vs. 2% of cats).

The study looked at prescribing of human-authorised medicines and revealed, to my mind, a relatively low level of prescribing: human medicines accounted for 5% of dog prescriptions; 3% of cats; 8% of rabbits. Of those used most commonly in dogs (see the table), two (metronidazole and tramadol) are now licensed as veterinary medicines. Ranitidine was commonly used in all species, despite cimetidine (another histamine H2 antagonist) being authorised for veterinary use. It would be interesting to understand more about the reasons for choosing ranitidine over cimetidine. 

Prescription of human medicines in veterinary practice

The most commonly prescribed antimicrobial was co-amoxiclav in dogs; third generation cephalosporins in cats; and fluroquinolones in rabbits. 

The research also revealed something about the extent of polypharmacy (co-prescription - concurrent administration of several medicines). Co-prescribing represented 40% of prescribing consultations for dogs; and 45% for cats; and 23% for rabbits. For dogs and rabbits the combination was most commonly an  antibiotic plus an anti-inflammatory while for cats in was an endoparasiticide plus endectocide

Research like this can help improve the safe and effective use of medicines. For example by helping to identify rare adverse events and variability in the efficacy or safety of medicines due to breed; develop knowledge about the safe use of human-authorised products in veterinary patients; understand how veterinary surgeons prescribe in addition to, or instead of, antibiotics to enhance antibiotic stewardship; and develop a better understanding of and be able to predict drug interactions. 

References

Singleton DA et al.New approaches to pharmacosurveillance for monitoring prescription frequency, diversity, and co-prescription in a large sentinel network of companion animal veterinary practices in the United Kingdom 2014–2016.Prev Vet Med 2018; 159: 153–61.https://www.ncbi.nlm.nih.gov/pubmed/30314778

Tauro A et al. Metronidazole-induced toxicity in 26 dogs. Aust Vet J 2018; 96: 495-501.

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