Evaluation of drug content (potency) for compounded and FDA-approved formulations of doxycycline on receipt and after 21 days of storage.

Objective: To determine drug content (potency) of compounded doxycycline formulations for veterinary use and of United States Food and Drug Administration (US FDA)-approved doxycycline formulations for human use < 24 hours after receipt (day 1) and after 21 days of storage under recommended conditions (day 21).

Design: Evaluation study.

Sample: FDA-approved doxycycline tablets (100 mg), capsules (100 mg), and liquid suspension (10 mg/mF), and compounded doxycycline formulations from three pharmacies (tablets [25, 100, and 150 mg; one product/source], chews [100 mg; one product/source], and liquid suspensions or solution [6 mg/mF, two sources and 50 mg/mF, one source]).

Procedures: Doxycycline content was measured in five samples of each tablet, chew, or capsule formulation and five replicates/bottle of liquid formulation on days 1 and 21 by liquid chromatography and compared to US Pharmacopeia acceptable ranges.

Results: All FDA-approved formulations had acceptable content on days 1 and 21. On day 1, mean doxycycline content for the three compounded tablet formulations was 89%, 98%, and 116% (3/5, 5/5, and 1/5 samples within acceptable ranges); day 21 content range was 86% to 112% (1/5, 5/5, and 4/5 samples within acceptable ranges). Day 1 content of chews was 81%, 78%, and 98% (0/5, 0/5, and 5/5 samples within acceptable ranges), and that of compounded liquids was 50%, 52%, and 85% (no results within acceptable ranges). No chews or compounded liquid formulations met USP standards on day 21.

Conclusions and clinical relevance: FDA-approved doxycycline should be prescribed when possible. Whole tablets yielded the most consistent doxycycline content for compounded formulations.

et al. J Am Vet Med Assoc. 2017;251:835-842.