Pharmacokinetics of doxycycline after administration as a single intravenous bolus and intramuscular doses to non-lactating Egyptian goats.

The pharmacokinetics of doxycycline hydrochloride (DoxHcl) at a dose of 5 mg kg-1 BW was studied after an intravenous (i.v.) bolus and intramuscular (i.m.) injections in non lactating goats. A microbiological assay employing Bacillus subtilis as the test organism was used to measure its concentrations in serum and urine. Following a single i.v. injection, the serum concentration-time curves of doxycycline hydrochloride were best represented by a two-compartment open model. The drug was rapidly distributed and slowly eliminated with half-lives of distribution (t1/2 alpha) and elimination (t1/2 beta) of 0.52 and 4.62 h, respectively. After i.m. injection of the same dose, the peak serum concentration C(max) was 1.60 microg ml-1 attained at 0.86 h (Tmax). Following i.v. and i.m. injections, the concentrations of doxycycline in urine were much higher than that in serum. Urinary drug concentrations decreased gradually till reaching its lowest detectable level 12 and 24h post-injections, respectively. The extent of serum protein binding percent was 32.8% and the systemic bioavailability was 99.40% after i.m. injection of 5 mg kg-1 BW