Loss of Drug Potency Found for Commonly Compounded Drug

A new study may have veterinarians rethinking how they use compounded formulations of doxycycline, a common antimicrobial prescribed to treat numerous bacterial infections in animals.

Researchers from Kansas State University compared FDA-approved formulations of doxycycline with compounded doxycycline obtained from 3 national compounding pharmacies. They measured doxycycline content from all formulations 1 day after receipt and then again 3 weeks later.

Results showed that the compounded formulations of doxycycline lost potency within 21 days of receipt, with many dropping to sub-therapeutic content in that time, as defined by United States Pharmacopeia standards. The complete report was recently published in the Journal of the American Veterinary Medical Association.

“These study results have important ramifications for practicing veterinarians,” said John Reddington, DVM, PhD, president and CEO of Morris Animal Foundation, which funded the study.

Veterinarians generally request compounded formulations of doxycycline when owners find it difficult to administer large tablets to their pets, or if there is a lack of FDA-approved doxycycline product available. Doxycycline is often used as an adjunct therapy for heartworm disease and to treat infectious diseases in cats and dogs, such as Rocky Mountain spotted fever and leptospirosis.

“Based on this study, we recommend avoiding compounded chews and liquid formulations,” explained Kate KuKanich, DVM, PhD, DACVIM (SAIM), one of the study’s lead researchers. “Although this was a relatively small study with only 3 pharmacies used, the results are consistent with results of random testing of other compounded products.”