PHARMACOKINETICS OF FLUNIXIN MEGLUMINE IN HEALTHY FOALS LESS-THAN 24 HOURS OLD

Objective-To determine pharmacokinetic variables that describe the dis position of flunixin after IV administration of flunixin meglumine to foals < 24 hours old. Animals-6 healthy foals, 2 males and 4 females ( mean age, 11.6 hours; range, 6 to 22.5 hours). Procedure-Flunixin (as flunixin meglumine) was administered to foals at a dosage of 1.1 mg/kg of body weight. Flunixin concentration in plasma samples was analyzed , using gas chromatography/mass spectroscopy. Concentration versus tim e profiles were analyzed according to standard pharmacokinetic techniq ues. Blood samples were obtained from foals by jugular venipuncture at defined intervals over a 48-hour period. Samples were centrifuged, an d plasma was frozen at -70 C until analyzed. One-, two-, and three-com partment analyses were conducted. The most appropriate model was deter mined by Akaike's information criterion analysis. Results-Plasma conce ntration versus time profiles were best described, using a two-compart ment open model. Clearance was significantly lower than that determine d for older foals and adult horses. Volume of distribution was larger than that determined for adults. Mean plasma half-life for healthy foa ls < 24 hours old was 8.5 hours. Conclusions and Clinical Relevance-Al though additional factors leg, dehydration or sepsis) must be consider ed on a case-by-case basis, flunixin meglumine should be administered differently to foals < 24 hours old, compared with adults. Under simil ar clinical circumstances, doses in foals should be increased by as mu ch as 1.5 times to induce comparable therapeutic concentrations; longe r dose intervals, on the basis of clinical response, would be necessar y to avoid drug toxicity.