Pharmacokinetic profile and behavioral effects of gabapentin in the horse |
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| Authors: | R L TERRY S M McDONNELL A W
Van EPS L R SOMA Y LIU C E UBOH P J MOATE B DRIESSEN |
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| Institution: | 1. Department of Clinical Studies‐New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA, USA;2. Pennsylvania Equine Toxicology and Research Center, West Chester University, West Chester, PA, USA;3. Department of Primary Industries, Ellinbank Centre, Ellinbank, VIC, Australia;4. Department of Anesthesiology, University of California, Los Angeles, David Geffen School of Medicine, Los Angeles, CA, USA |
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| Abstract: | Terry, R. L., McDonnell, S. M., van Eps, A. W., Soma, L. R., Liu, Y., Uboh, C. E., Moate, P. J., Driessen, B. Pharmacokinetic profile and behavioral effects of gabapentin in the horse. J. vet. Pharmacol. Therap. 33 , 485–494. Gabapentin is being used in horses although its pharmacokinetic (PK) profile, pharmacodynamic (PD) effects and safety in the equine are not fully investigated. Therefore, we characterized PKs and cardiovascular and behavioral effects of gabapentin in horses. Gabapentin (20 mg/kg) was administered i.v. or p.o. to six horses using a randomized crossover design. Plasma gabapentin concentrations were measured in samples collected 0–48 h postadministration employing liquid chromatography‐tandem mass spectrometry. Blood pressures, ECG, and sedation scores were recorded before and for 12 h after gabapentin dosage. Nineteen quantitative measures of behaviors were evaluated. After i.v. gabapentin, the decline in plasma drug concentration over time was best described by a 3‐compartment mammillary model. Terminal elimination half‐life (t1/2γ) was 8.5 (7.1–13.3) h. After p.o. gabapentin terminal elimination half‐life ( ) was 7.7 (6.7–11.9) h. The mean oral bioavailability of gabapentin (±SD) was 16.2 ± 2.8% indicating relatively poor absorption of gabapentin following oral administration in horses. Gabapentin caused a significant increase in sedation scores for 1 h after i.v. dose only (P < 0.05). Among behaviors, drinking frequency was greater and standing rest duration was lower with i.v. gabapentin (P < 0.05). Horses tolerated both i.v. and p.o. gabapentin doses well. There were no significant differences in  and  . Oral administration yielded much lower plasma concentrations because of low bioavailability. |
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