Penciclovir pharmacokinetics after oral and rectal administration of famciclovir in African elephants (Loxodonta africana) shows that effective concentrations can be achieved from rectal administration, despite lower absorption.

ABSTRACT

OBJECTIVE: To evaluate the pharmacokinetics of famciclovir and its metabolite penciclovir following a single dose administered orally and rectally in African elephants (Loxodonta africana). ANIMALS 15 African elephants (6 males and 9 females) of various ages. METHODS: Famciclovir (15 mg/kg) was administered orally or per rectum once, with at least a three-week washout period between administrations. Blood was collected at 13 different timepoints per administration for 6 elephants, occurring between February and March 2020. An additional 9 elephants were sampled at variable timepoints per administration utilizing a sparse sampling design between July 2020 and January 2021. Plasma famciclovir and penciclovir levels were measured via HPLC and fluorescence detection. Pharmacokinetic analysis was completed in the summer of 2021 using noncompartmental analysis and nonlinear mixed-effects modeling. RESULTS: Famciclovir was not detected in any sample, suggesting complete metabolism. Key pharmacokinetic parameters for penciclovir following oral administration were time to maximum concentration (tmax; 2.12 hours), area under the concentration-versus-time curve (AUC; 33.93 µg·h/mL), maximum observed concentration (Cmax; 3.73 µg/mL), and absorption half-life (t1/2; 0.65 hours). Following rectal administration, the values were tmax, 0.65 hours; AUC, 15.62 µg·h/mL; Cmax, 2.52 µg/mL; and absorption t1/2, 0.13 hours. CONCLUSIONS: Famciclovir was rapidly metabolized to penciclovir. Oral administration resulted in slower absorption but higher maximum plasma concentration and higher AUC compared to rectal administration. CLINICAL RELEVANCE African elephants administered famciclovir via oral and rectal routes resulted in measurable serum penciclovir, and these findings may be utilized by clinicians treating viral infections in this species.