%0 Journal Article
%T Comparative pharmacokinetics of phenylbutazone in healthy young-adult and geriatric horses.
%A Zaghloul IY
%A Bedenice D
%A Ceresia ML
%A Jones PH
%A Sanchez-Londono A
%A Lobo MN
%A Böhlke M
%A Paradis MR
%J Am J Vet Res
%V 0
%N 0
%D 2024 Jun 28
%M 38942059
%F 1.055
%R 10.2460/ajvr.24.01.0012
%X <B>OBJECTIVE: </B>To evaluate the effects of aging on phenylbutazone (PBZ) disposition in older horses (≥ 25 years old) compared to young adults (4 to 10 years old) by characterizing the pharmacokinetic profile of PBZ and its active metabolite, oxyphenbutazone (OPBZ), following a 2.2-mg/kg dose, IV. We hypothesized that the disposition of PBZ will be affected by age.<BR><B>METHODS: </B>16 healthy horses (8 young adults aged 4 to 10 years and 8 geriatric horses ≥ 25 years old).<BR><B>METHODS: </B>Horses were administered a single 2.2-mg/kg PBZ dose, IV. Plasma samples were collected at designated time points and frozen at -80 °C until assayed using liquid chromatography-tandem mass spectrometry. Pharmacokinetic analyses were performed using Phoenix WinNonlin, version 8.0 (Certara). Both clinical and pharmacokinetic data were compared between age groups using independent samples t tests, with P < .05 considered significant.<BR><B>RESULTS: </B>Baseline characteristics did not differ between groups, with the exception of age, weight, and plasma total solids. Plasma concentrations of PBZ were best described by a two-compartment model. The maximum plasma concentration of OPBZ was reached at 5 hours for both age groups, and the metabolite-to-parent-drug area-under-the-curve ratios were approximately 20% for both groups. None of the pharmacokinetic parameters of PBZ or its metabolite, OPBZ, differed significantly between age groups.<BR><B>CONCLUSIONS: </B>The hypothesis was rejected as there was no significant difference in PBZ disposition in young-adult horses compared to geriatric horses. Our data do not support the need for dose adjustments of PBZ in clinically healthy geriatric horses.