Abstract :
The pharmacokinetics of amoxicillin following a single intravenous (i.v.) and intramuscular
(i.m.) administration of a conventional sodium formulation and following a single i.m.
administration of a trihydrate long acting suspension was investigated in adult llamas. On
phase 1, in a cross-over design, six llamas received sodium amoxicillin (20 mg/kg) by the
i.v. and i.m. routes. On phase 2, six llamas received i.m. trihydrate amoxicillin suspension
(15 mg/kg). Amoxicillin plasma concentrations were determined using a microbiological
assay. Significant differences were found for mean peak plasma concentration (40.4 ± 12.1
versus 3.04 ± 1.02 g/ml), mean elimination half-life (0.86 ± 0.3 versus 9.96 ± 3.1 h) and
mean residence time (1.37 ± 0.5 versus 15.1 ± 4.1 h) following sodium and trihydrate i.m.
amoxicillin, respectively. Bioavailability was similar for both sodium (1.44 ± 0.2) and trihydrate
(1.14 ± 0.4) formulations. The results of the pharmacokinetic/pharmacodynamic
indices of time above the minimal inhibitory concentrations (T > MIC) suggest that 20 mg/kg
sodium amoxicillin would produce a good therapeutic outcome in infections due to susceptible
bacteria administered every 8–12 h, while for 15 mg/kg trihydrate amoxicillin, higher
doses or more frequent intervals may be needed for treating low susceptibility bacteria in
llamas
