Midazolam is a benzodiazepine that is used as a sedative and hypnotic in human and veterinary medicine.1–6 Midazolam has been recommended for sedation prior to induction of anesthesia with ketamine in camelids, but the authors could not find reports describing the pharmacokinetics or pharmacodynamics properties of this drug in alpacas.7,8 The pharmacokinetic properties of midazolam have been described in humans, dogs, and sheep.9–11 The disposition of midazolam in humans has been described by a 2-compartment open model.10 Midazolam has a half-life of approximately 2 hours, an apparent volume of distribution of 1.1 L/kg, and a total clearance of 0.38 L/kg/h in humans.10 Absorption is rapid and complete after IM administration in dogs, with an apparent volume of distribution of 3 L/kg and a mean elimination half-life of 1.28 hours.9 Plasma half-lives in both pregnant ewes and fetal lambs are approximately 1.5 hours and associated with high heart rates and mean arterial blood pressures.11 Intramuscular administration of midazolam (0.4 mg/kg) causes sedation and sternal recumbency in goats, with higher doses causing loss of consciousness and lateral recumbency.5 Midazolam causes weakness, ataxia, and transient agitation in dogs and may result in analgesia in sheep.9,12 High heart rates with increases in respiratory rates are observed at higher doses.5 The duration of anesthesia when midazolam is combined with ketamine in goats ranges from 16 to 39 minutes.5
Midazolam has been used in camelids for sedation prior to anesthesia and as part of balanced anesthetic techniques.13,14 Midazolam (0.25 mg/kg, IV) and ketamine (5 mg/kg, IV) have been used to induce anesthesia in alpacas prior to maintenance of anesthesia with isoflurane in a study13 assessing the effects of dobutamine and norepinephrine. Prior to catecholamine administration, heart rate was within reference range, and mean arterial blood pressure, central venous pressure, systemic vascular resistance, and stroke volume were decreased but within expected values for anesthetized alpacas.13 In a case report,14 a balanced anesthetic technique including midazolam, fentanyl, ketamine, and isoflurane was successfully used to provide anesthesia for extensive dental surgery of a female alpaca.
The purpose of the study reported here was to determine the pharmacokinetics of midazolam after IV and IM administration and determine its sedative effects and effects on heart rate and respiratory rate in alpacas.
Area under the concentration versus time curve
Maximum sedation score
Xylazine, Vedco Inc, St Joseph, Mo.
Lidocaine, Vedco Inc, St Joseph, Mo.
Angiocath, Parke, Davis & Co, Sandy, Utah.
Surflo catheter, Terumo Medical Corp, Elkton, Md.
Midazolam, Hospira Inc, Lake Forest, Ill.
Midazolam, United States Pharmacopeia, Rockville, Md.
Nevirapine, Boehringer Ingelheim Pharmaceutics Inc, Ridgefield, Colo.
TSQ Vantage triple stage quadrupole mass spectrometer, ThermoFisher Scientific, San Jose, Calif.
LC-20AD HPLC pump, Shimadzu, Columbia, Md.
LC-20AC Autosampler, Shimadzu, Columbia, Md.
Betabasic, 8 column, ThermoFisher Scientific, San Jose, Calif.
WinNonlin, version 5.2, Pharsight Corp, St Louis, Mo.
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