A novel subcutaneous controlled-release amoxicillin degradable implant for extended-interval administration in veterinary medicine

Dosage forms of antimicrobials play a critical role in facilitating the attainment of pharmacokinetic-pharmacodynamic (PK-PD) targets as well as adherence in both veterinary and human medicine. The purpose of this study was to develop and evaluate a controlled-release subcutaneous amoxicillin implant for single-dose therapy of large ruminants such as goats, sheep, and deer. The degradable implant, designed to attain PK-PD targets following single administration, was evaluated for amoxicillin release rate and time-concentration profile. In vitro release studies demonstrated constant-rate release of approximately 40% of amoxicillin content within 96h. In an in vivo study in goats, serving as a model for target animals, a serum concentration of approximately 0.4mg/L was achieved within 8h of implant insertion and maintained for >6days. In comparison, in control goats given a standard single intramuscular amoxicillin dose of 15mg/kg, amoxicillin peaked at 1.2mg/L after 1h, rapidly dropping to below detection level at 8h. These results suggest that the proposed implant offers a unique modality for animal caregivers to conveniently administer a full antimicrobial course following a single dose of an efficient PK-PD-optimized dosage form. Furthermore, modifications of implant composition may allow for tailoring of its characteristics to various PK, PD, microbiological, and clinical requirements.