Pharmacokinetics of neomycin in sheep after intravenous, intramuscular, subcutaneous and intratracheal administration.

The pharmacokinetics and bioavailability of neomycin in sheep were investigated following intravenous, intramuscular, subcutaneous and intratracheal administration of 10 mg/kg. A rapid distribution phase (t 1/2 alpha, 3.16 min) was followed by a slower elimination phase (t1/2 beta, 1.98 h). The apparent volume of distribution was 304.69 ml/kg. Absorption half-lives were 18.62, 21.22 and 40.83 min and elimination half-lives 2.68, 2.82 and 2.55 h after IM, SC and IT administration, respectively. Bioavailabilities between 0.74 and 0.85 were obtained for the three routes of administration. Based on the bioavailability and disposition kinetics of neomycin, a twice daily IM dosage regimen should both be practical and adequate to maintain plasma neomycin concentrations within the pharmacologically active but nontoxic range.