Pharmacokinetic study of an injectable long-acting parenteral formulation of doxycycline hyclate in calves

Doxycycline hyclate (DOX-h) can be regarded as a time-dependant antibacterial. Hence, a parenteral long-acting formulation may be regarded as more pharmacologically sound. A poloxamer-based matrix was used to produce a long-acting injectable preparation (DOX-h-LA) and its serum concentrations vs. time profile investigated after its s.c. injection to calves. Serum concentrations profiles for such a prepartion were compared to the corresponding profiles obtained with an aqueous formulation of DOX-h injected either i.m. or i.v. in 10 calves in a crossover study at dose of 10 mg/kg, with washout periods. DOX-h-LA showed the greatest values for bioavailability (602%); maximum serum concentration (Cmax) value was 1.99 μg/mL with a time to reach Cmax (Tmax) of 25 h and an elimination half-life of 40.81 h. Considering minimum effective serum concentration of 0.5 μg/mL a dose-interval of 80 h can be achieved for DOX-h-LA, and only 9.7 h and 17 h after the i.v. or i.m. administration of DOX-h, respectively.