Antipyrine pharmacokinetics and urinary excretion in female horses.
OBJECTIVE
To measure renal clearance of antipyrine and urinary excretion of antipyrine (AP) metabolites in horses by use of validated high-performance liquid chromatography (HPLC) methods.


METHODS
8 Standardbred mares.


METHODS
HPLC methods for measurement of AP in equine plasma and AP and its metabolites in equine urine were validated. Antipyrine (20 mg/kg of body weight) was administered i.v., and blood samples and urine specimens were collected over 24 hours.


RESULTS
Median plasma clearance of AP in horses was 6.2 ml/min/kg, of which < 2% could be attributed to renal clearance. Urinary excretion of AP and its metabolites over 24 hours accounted for < 22% of the AP dose administered. The major metabolite of AP in urine was 4-hydroxyantipyrine.


CONCLUSIONS
Use of the proven validated methods for measuring AP and its metabolites indicated that AP has minimal renal clearance in horses, suggesting that plasma clearance of AP reflects hepatic clearance. Combined with AP metabolite data, the pharmacokinetics of AP may be useful for assessment of hepatic cytochrome P450 activity in horses.
Dyke
T M
TM
Analytical Toxicology Laboratory, College of Veterinary Medicine, Ohio State University, Columbus 43210-1089, USA.
Sams
R A
RA
Hinchcliff
K W
KW
D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D000983:Antipyrine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000493:pharmacokinetics* / Q000652:urine; D001711:Biotransformation; D005260:Female; D006736:Horses; D007275:Injections, Intravenous; D007668:Kidney / Q000502:physiology; D008657:Metabolic Clearance Rate; D013997:Time Factors
D000894:Anti-Inflammatory Agents, Non-Steroidal; D000983:Antipyrine