The disposition of suxibuzone in the horse.

This research article presents a method for determining the anti-inflammatory drug suxibuzone and its metabolites in horse plasma and urine, and explains their observed dispositions in the horse’s system.

Method of Analysis

• The researchers utilized a high performance liquid chromatographic method to trace the anti-inflammatory drug suxibuzone (SXB) and its primary metabolites – phenylbutazone (PBZ) and oxyphenbutazone (OPBZ) in equine plasma and urine.

Observations Post Administration

• When 6 mg/kg of suxibuzone was administered either intravenously or orally, no parent drug (SXB) was detected in the horse’s blood (plasma) or urine.
• Regardless, the metabolite PBZ was observed following its intravenous administration. The disposition of this metabolite could be described using a two-compartment model, and it had a half-life ranging from 7.40 to 8.35 hours.
• Due to the adverse effects identified with intravenous (i.v.) usage, the research discourages using suxibuzone in this manner with horses.
• Both PBZ and OPBZ were identified in the equine plasma and urine following oral (p.o.) administration of suxibuzone.

Findings Regarding Metabolite Concentrations

• Peak plasma PBZ concentrations were observed 6 hours post oral administration and were noted as 8.8 +/- 3.0 micrograms/ml.
• The terminal exponential constant was 0.11 +/- 0.01 h-1.
• Interestingly, both phenylbutazone and oxyphenbutazone were detectable in urine (greater than 1 microgram/ml) for at least 36 hours, following p.o. administration.

Drug Interaction with Equine Body

• In vitro experiments showed that suxibuzone does not get hydrolyzed by horse plasma. However, equine liver homogenates exhibited a potent capacity for hydrolyzing SXB.
• This high capacity of equine liver to process SXB hints towards the ‘first-pass effect’, which could be the reason for the rapid disappearance of this non-steroidal anti-inflammatory drug (NSAID) in horses.