Pharmacokinetics of flunixin meglumine in healthy foals less than twenty-four hours old.
OBJECTIVE
To determine pharmacokinetic variables that describe the disposition of flunixin after i.v. administration of flunixin meglumine to foals < 24 hours old.


METHODS
6 healthy foals, 2 males and 4 females (mean age, 11.6 hours; range, 6 to 22.5 hours).


METHODS
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 time profiles were analyzed according to standard pharmacokinetic techniques. Blood samples were obtained from foals by jugular venipuncture at defined intervals over a 48-hour period. Samples were centrifuged, and plasma was frozen at -70 C until analyzed. One-, two-, and three-compartment analyses were conducted. The most appropriate model was determined by Akaike's information criterion analysis.


RESULTS
Plasma concentration versus time profiles were best described, using a two-compartment open model. Clearance was significantly lower than that determined for older foals and adult horses. Volume of distribution was larger than that determined for adults. Mean plasma half-life for healthy foals < 24 hours old was 8.5 hours.


CONCLUSIONS
Although additional factors (eg, dehydration or sepsis) must be considered on a case-by-case basis, flunixin meglumine should be administered differently to foals < 24 hours old, compared with adults. Under similar clinical circumstances, doses in foals should be increased by as much as 1.5 times to induce comparable therapeutic concentrations; longer dose intervals, on the basis of clinical response, would be necessary to avoid drug toxicity.
Crisman
M V
MV
Department of Large Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute, Blacksburg 24061, USA.
Wilcke
J R
JR
Sams
R A
RA
D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D003002:Clonixin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics; D005260:Female; D006736:Horses; D007275:Injections, Intravenous; D008297:Male; D008657:Metabolic Clearance Rate; D008954:Models, Biological
D000894:Anti-Inflammatory Agents, Non-Steroidal; C014558:flunixin meglumine; D003002:Clonixin