Disposition and excretion of 6-methoxy-2-naphthylacetic acid, the active metabolite of nabumetone in horses.
OBJECTIVE
To examine, in horses, the disposition and excretion of the active metabolite 6-methoxy-2-naphthylacetic acid (6MNA) of the nonsteroidal anti-inflammatory prodrug nabumetone.


METHODS
Pharmacokinetic analysis of 6MNA after oral administration of nabumetone and IV administration of 6MNA.


METHODS
Using a crossover design, 5 horses were orally administered 3.7 mg of nabumetone/kg of body weight. After a 3-week washout period, 4 horses were administered 2.5 mg of 6MNA/kg, IV.


RESULTS
Absorption of nabumetone from the gastrointestinal tract and its metabolism to 6MNA had a median appearance half-life of 0.88 hour. The elimination half-life was 11 hours. Area under the plasma concentration time curve for 6MNA after oral administration of nabumetone was 120.6 mg/h/L. A dose of 2.5 mg/kg of 6MNA administered IV resulted in plasma concentration nearly equivalent to that induced by the orally administered dose. Disposition of 6MNA was modeled as a one-compartment, first-order elimination. The area under the plasma concentration time curve for IV administration of 6MNA was 117.0 mg/h/L, and the specific volume of distribution was 0.247 L/kg. The distribution half-life and the elimination half-life were 0.56 and 7.90 hours, respectively. Percentage of total dose recovered in urine for the 36-hour collection period after the oral and IV administrations was 7.4 and 5.3%, respectively.


CONCLUSIONS
Metabolism of nabumetone to 6MNA, as reported in other species, also occurs in horses. There were a number of additional metabolites of nabumetone in urine that could not be fully identified and characterized.
Soma
L R
LR
School of Veterinary Medicine, University of Pennsylvania 19348, USA.
Uboh
C E
CE
Rudy
J A
JA
Smith
M S
MS
D000284:Administration, Oral; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D002074:Butanones / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D018592:Cross-Over Studies; D005260:Female; D006207:Half-Life; D006736:Horses; D007408:Intestinal Absorption; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D015394:Molecular Structure; D000077430:Nabumetone; D009280:Naphthaleneacetic Acids / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine
D000894:Anti-Inflammatory Agents, Non-Steroidal; D002074:Butanones; D009280:Naphthaleneacetic Acids; C044612:6-methoxy-2-naphthylacetic acid; D000077430:Nabumetone