Determination of Acepromazine, Ketamine, Medetomidine, and Xylazine in Serum: Multi-Residue Screening by Liquid Chromatography-Mass Spectrometry

A large variety of drugs are administered to large and small animals by veterinary clinicians for sedation, anesthesia, muscle relaxation, and analgesia. The present paper reports a simple and rapid multi-residue detection and quantitation method for four chemically different drugs: medetomidine, xylazine, ketamine, and acepromazine. Chromatographic separation was carried out on a liquid chromatography-mass spectrometry instrument with a C18-reversed-phase column. Fragmentation patterns were determined with atmospheric pressure chemical ionization mass spectrometry set to operate in a positive selective ion monitoring mode. The method was determined to be linear over the range of concentrations tested (2.0-100.0 ng/mL). Accuracy, precision, and specificity were evaluated and the method was determined to be applicable to detection of medetomidine, xylazine, ketamine, and acepromazine in serum samples of multiple animal species (canine, equine, and bovine). Matrix limits of quantitation were determined to be 5.0 ng/mL for all four analytes, and recoveries ranged between 82.0 and 118%, with a 3.0-18.3% relative standard deviation.

A previously unidentified acepromazine metabolite in humans: implications for the measurement of acepromazine in blood

High-performance liquid chromatography-diode-array detection results obtained during the investigation of two cases involving acepromazine prompted us to study the stability of the drug in blood. It was found that acepromazine can undergo in vitro conversion by human red blood cells to 2-(1-hydroxyethyl)promazine, a product that has been reported as a minor urinary metabolite in horse urine but not previously identified in humans. Further, our analytical findings in the two cases examined suggest that 2-(1-hydroxyethyl)promazine may be the major unconjugated metabolite of acepromazine in humans. These findings have important implications for the analytical toxicology of acepromazine.

A fatality involving two unusual compounds--zolpidem and acepromazine

A fatality due to ingestion of zolpidem, a recently developed nonbenzodiazepine hypnotic, and acepromazine, a phenothiazine sedative used in veterinary practice, is reported. Both drugs were identified and quantified using high-performance liquid chromatography with diode-array detection. Zolpidem and acepromazine blood concentrations were 3.29 and 2.40 micrograms/ml, respectively. It is the first report of a death involving either of these two drugs. The results are discussed in the light of the existing literature and may suggest a reciprocal potentiation of the toxic effects of zolpidem and phenothiazines.

Development of an enzyme-linked immunosorbent assay for the detection of phenothiazine tranquillisers in horses

An acepromazine (ACP) hapten was synthesised, coupled to bovine serum albumin and injected into a horse to produce antibodies to the drug. A competitive ELISA was developed whereby ACP attached to the solid phase via lysozyme competed with free ACP present in phosphate buffered saline, horse serum or horse urine for limiting amounts of antibody. The assay could detect the presence of ACP and, or, some of its metabolites in horse urine for at least 25 hours after intravenous injection of 0.1 mg kg-1 ACP maleate, but because of non-specific interference, horse serum could not be used. As little as 0.24 micrograms ml-1 ACP or its metabolites could be detected. The level of detection and the ease of performance of the assay make it an attractive alternative to the more complex methods currently available for the screening of horse urine samples at horse races, shows and sales.

The pharmacokinetics, pharmacological responses and behavioral effects of acepromazine in the horse

After intravenous (i.v.) injection, acepromazine was distributed widely in the horse (Vd = 6.6 litres/kg) and bound extensively (greater than 99%) plasma proteins. Plasma levels of drug declined with an alpha half-life of 4.2 min, while the beta phase or elimination half-life was 184.8 min. At a dosage level of 0.3 mg/kg acepromazine was detectable in the plasma for 8 h post dosing. The whole blood partitioning of acepromazine was 46% in the plasma phase and 54% in the erythrocyte phase. Penile prolapse was clearly evident at doses from 0.01 mg/kg to 0.4 mg/kg i.v., and the duration and extent of protrusion were dose related. Hematocrit levels were significantly lowered by administration of 0.002 mg/kg i.v. (about 1 mg to a 500 kg horse) and increasing dosages resulted in greater than 20% lowering of the hematocrit from control levels. Pretreatment of horses with acepromazine also reduced the variable interval (VI 60) responding rate in all horses tested. These data show that hematocrit changes are the most sensitive pharmacological responses to acepromazine, followed by changes in penile extension, respiratory rate, VI responding and locomotor responses. Acepromazine is difficult to detect in plasma at normal clinical doses. However, because of its large volume of distribution, its urinary elimination is likely prolonged, and further work on its elimination in equine urine is required.

Atypical conditions for quantitative recovery of acepromazine and chlorpromazine from plasma

Recoveries of acepromazine and chlorpromazine from equine plasma were examined. Recoveries of both drugs from plasma were poor under theoretically optimal conditions for basic drugs. When a wide range of extraction pH was examined, it was found that more complete recoveries of these drugs from plasma were achieved at pH 5-6. Use of [3H] chlorpromazine showed that the rate of migration of the drug from an aqueous to a nonpolar environment was much faster at pH 6.0 than at pH 9.2 from both plasma and buffer solutions. Times required for equilibration with agitation were 15 min at pH 6.0, 1 h at pH 9.2, and 2 h at pH 11.0. With these agitation times and pH values, recoveries were more than 95% complete.