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The pharmacokinetics of gabapentin in cats

Adrian, Derek, Papich, Mark G., Baynes, Ronald, Stafford, Emma, Lascelles, B. Duncan X.
Journal of veterinary internal medicine 2018 v.32 no.6 pp. 1996-2002
bioavailability, blood sampling, cats, drug therapy, drugs, gels, half life, intravenous injection, mass spectrometry, mixed breeds, models, musculoskeletal system, oral administration, pain, pharmacokinetics, ultra-performance liquid chromatography
BACKGROUND: Gabapentin is the most commonly prescribed medication for the treatment of chronic musculoskeletal pain in cats. Despite this common and chronic usage, clinically relevant pharmacokinetic data is lacking. OBJECTIVES: To evaluate the pharmacokinetics of clinically relevant dosing regimens of gabapentin in cats. ANIMALS: Eight research‐purpose mixed‐breed cats. METHODS: Cats were enrolled in a serial order, non‐randomized pharmacokinetic study. Gabapentin was administered as an IV bolus (5 mg/kg), orally (10 mg/kg) as a single dose or twice daily for 2 weeks, or as a transdermal gel (10 mg/kg) in serial order. Serial blood samples were collected up to 48 hours. Plasma concentrations were determined using Ultra Performance Liquid Chromatography‐Mass Spectrometry. Compartmental analysis was used to generate gabapentin time‐concentration models. RESULTS: After IV administration CL (median (range)) and terminal half‐life were 160.67 mL/kg*hr (119.63‐199.11) and 3.78 hours (3.12‐4.47), respectively. The oral terminal half‐life was 3.63 hours (2.96‐4.77), and 3.72 hours (3.12‐4.51) for single and repeated dosing. TMAX and CMAX, as predicted by the model were 1.05 hours (0.74‐2.11), and 12.42 μg/mL (8.31‐18.35) after single oral dosing, and 0.77 hours (0.58‐1.64), and 14.78 μg/mL (9.70‐18.41) after repeated oral dosing. Bioavailability after a single oral dose was 94.77% (82.46‐122.83). IMPORTANCE: Repeated oral dosing of gabapentin did not alter the drug's pharmacokinetics, making dose adjustments unnecessary with long‐term treatment. As prepared, the transdermal route is an inappropriate choice for drug administration. These relevant data are important for future studies evaluating potential efficacy of the medication for treating chronic pain states in cats.