Analgesia in camelids has been described for certain drugs including xylazine,1 lidocaine,1 flunixin meglumine,2 and butorphanol3; however, to our knowledge, neither the effects nor the disposition of morphine has been studied in camelids. Morphine is the prototypic opiate administered for pain relief in human and animal medicine.4 It is classified as a M and K opioid receptor agonist, and it binds to opiate receptors in the central and peripheral nervous system to inhibit the release of pain-related neurotransmitters.5 The safety and efficacy of morphine have been studied in dogs and cats,4,6-11 but limited research has been performed in large domesticated animals.12–19 Concern for adverse effects and lack of proper dosage information for morphine in camelids has limited its clinical use. Adverse effects in other species include bradycardia,4 respiratory depression,4,20 CNS depression,4,20 ileus,12,14,17 excitement or dysphoria,6,15 and altered thermoregulation.21–25 Little is known about appropriate dosage of morphine in camelids by any route, and doses are often based on speculation, extrapolation from other species, and clinical impression. Basing effectiveness of analgesia on clinical impression can be misleading because behaviors reflecting pain are often subtle or difficult to recognize.16,20 Sedation can mask these behaviors for which assessment is subjective, and close observation of the animal in its environment is required for accurate pain assessment.16
The purpose of this project was to assess the pharmacokinetics of varying morphine doses administered via different routes to llamas, compare the pharmacokinetics of morphine in llamas with other species, describe the pharmacodynamic response of llamas to varying doses of morphine administered IV, and determine the relationship between pharmacodynamics and plasma morphine concentrations in llamas. The hypotheses of this study were that analgesia will increase as the dose of morphine increases, sedation will occur after morphine administration, and physiologic parameters will be affected by morphine administration. The goal of this study was to generate therapeutic guidelines for administration of morphine sulfate in llamas.
Area under the curve from time 0 to infinity
Plasma concentration at time 0
Volume of distribution at steady state
Morphine sulfate, Baxter Healthcare Corp, Deerfield, Ill.
Llama restraint chute, Great Divide, Masonville, Colo.
2% lidocaine HCl injection, USP, Abbott Laboratories, North Chicago, Ill.
Intracath, IV catheter/needle unit, Becton Dickinson Vascular Access, Sandy, Utah.
Clinical Pharmacology Laboratory, College of Veterinary Medicine, North Carolina State University, Raleigh, NC.
BD Insyte IV catheter, Becton Dickinson Infusion Therapy Systems Inc, Sandy, Utah.
Bunny Pads Bunny electrodes, Lead-Lok Inc, Sandpoint, Idaho.
Voltage stimulator, Grass Medical Instruments, Quincy, Mass.
WinNonlin, version 4.0, Pharsight Corp, Mountain View, Calif.
PROC MIXED, SAS version 9.1, SAS Institute Inc, Cary, NC.
PROC GLM, SAS version 9.1, SAS Institute Inc, Cary, NC.
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