In vivo release of oxytetracycline from a biodegradable controlled‐release gel injected subcutaneously in Japanese quail ( Coturnix coturnix japonica )

A long‐acting, biodegradable, controlled‐release formulation of oxytetracycline (CR‐OTC) was evaluated in 18 adult Japanese quail ( Coturnix coturnix japonica ) following a single subcutaneous (s.c.) injection. Prior to characterizing the release of oxytetracycline (OTC) from the CR‐OTC, the pharmacokinetic parameters of intravenously (i.v.) administered OTC were determined. Concentrations of free OTC were measured using a bioassay. The plasma concentration–time profile of OTC after a single i.v. injection at 20 mg/kg was best fit to an open two‐compartmental model, with the following pharmacokinetic parameters: area under the curve ( AUC ) = 36.72 mg · h/L, terminal elimination half‐life = 2.34 h, clearance ( Cl ) = 0.545 L/kg/h. Plasma [OTC] was >1.0  μ g/mL for at least 4 h following i.v. injection. The CR‐OTC gel was well tolerated at a dosage of 1500 mg/kg s.c. Plasma [OTC] rose to >1.0  μ g/mL within 24 h; it remained >1.0  μ g/mL for at least 10 days in all birds sampled at that time point ( n  = 9) and for at least 18 days in two of nine birds. Using a deconvolution technique, it was determined that approximately 54.8% of the administered OTC was released from the CR‐OTC over the 45‐day observation period. This long‐acting, biodegradable controlled‐release OTC formulation may have potential for the treatment of chlamydophila infections and other OTC‐sensitive bacteria in Japanese quail, however further studies are necessary to determine its safety and clinical application.