Disposition of human drug preparations in the horse. VI. Tiaprofenic acid.

Urinary and plasma concentrations of the nonsteroidal anti-inflammatory drug tiaprofenic acid were determined following oral and intramuscular administration of a dose of 1 g to five fasted horses. Quantitation was performed by high-performance liquid chromatography (HPLC). The limit of quantitation (LOQ) was 0.1 microg/ml and 0.5 microg/ml in 2 ml plasma and 1 ml urine, respectively. Assay precision and extraction recovery were between acceptable values. Tiaprofenic acid pharmacokinetics were described by non-compartment analysis of the data. Absorption was faster after oral administration as maximum plasma concentrations (oral: 6.0+/-3.3 microg/ml; intramuscular: 6.6+/-2.5 microg/ml) were obtained after 1 h (oral) compared to 1.6+/-0.4 h (intramuscular) post dosage. Plasma binding (66+/-3%) was lower than measured in other species. Tiaprofenic acid was detected in urine for at least 24 h. The percentage of the parent drug excreted in the first 12 h after oral and intramuscular administration was 38+/-6% and 34+/-5%, respectively.