BIOAVAILABILITY OF KETOPROFEN IN HORSES AFTER RECTAL ADMINISTRATION

Six healthy mares ranging in age from 6 to 12 years and weighing from 415 to 540 kg were used to determine the rectal bioavailability of ket oprofen. For the rectal administration, three different formulations, each containing Ig of ketoprofen, were administered in a fatty and a h ydrophilic suppository base and as a liquid suspension. An average eli mination half-life of 1.3 h (+/- 1.2) was found. The average value for the total plasma clearance (CIT) was 131.9 mL/min . kg (range 95-183. 5). The volume of distribution V-d(area) was 255 mL/kg and the mean re sidence time (MRT) Value was 0.47 h. After rectal administration, the mean maximal plasma ketoprofen concentrations were 1.6(+/- 0.8), 1.1(/- 0.7) and 1.6(+/- 0.2) mu g/mL for the fatty suppository, the hydrop hilic suppository and the liquid suspension respectively. The absolute bioavailability of ketoprofen in horses after rectal administration o f the three formulations was relatively low, with a large interindivid ual variability (24.5 +/- 9.5%, 28.7 +/- 18% and 31.3 +/- 6.8% for the fatty suppository, the hydrophilic suppository and the liquid suspens ion respectively). These Values were not significantly different (P = 0.05; Friedman test). Despite the low rectal bioavailability obtained in this study, there was some evidence for the clinical effectiveness of the rectal formulations.