PHARMACOKINETICS OF KETOPROFEN IN HEALTHY FOALS LESS-THAN 24 HOURS OLD

Objective-To determine pharmacokinetic variables that describe disposi tion of ketoprofen after its IV administration to foals < 24 hours old . Animals-8 healthy foals (1 male and 5 females); mean age, 12.5 (rang e, 8.5 to 17) hours at time of dose administration. Procedure-Ketoprof en was administered IV to foals at a dosage of 2.2 mg/kg of body weigh t. Ketoprofen concentration in plasma samples was analyzed, using high -performance liquid chromatography. Concentration versus time profiles were analyzed according to standard pharmacokinetic techniques. Blood samples were obtained from foals by jugular venipuncture at defined t imes during a 48-hour period. Samples were centrifuged, and plasma was frozen at -70 C until analyzed. One-, two-, and three-compartment ana lyses were conducted. The most appropriate model was determined by use of Akaike's information criterion analysis. Results-Plasma concentrat ion versus time profiles were best described, using a two-compartment open model. Clearance (normalized for body weight) was significantly l ower than that determined for adult horses. Volume of distribution (no rmalized for body weight) was larger than that determined for adult ho rses. Mean (harmonic) plasma half-life for healthy foals < 24 hours ol d was 4.3 hours. Clinical Relevance-Although additional factors, such as dehydration or sepsis, must be considered on a case-by-case basis, the dose of ketoprofen administered to foals < 24 hours old should be different from the dose administered to adult horses. Under similar cl inical circumstances, doses in foals should be increased by as much as 1.5 times to produce comparable therapeutic concentrations; longer do se intervals, based on clinical response, would be necessary to avoid drug toxicity.