Gabapentin (20 mg/kg orally once 1-2 hours prior to visit) has become popular as a medication prescribed to reduce stress and improve compliance in feline patients during veterinary visits. However this dose may be inappropriate for elderly cats, specifically those with chronic kidney disease (CKD) as gabapentin is cleared only by renal excretion. Therefore the purpose of this study was to assess the pharmacokinetics of gabapentin in cats with CKD in comparison to clinically healthy cats using a limited-sampling approach. Apparently healthy cats and cats with stable IRIS Stage 2 and 3 CKD were enrolled. Diagnostic tests required before enrollment included serum biochemistry profile, complete blood count, urinalysis, blood pressure, and serum total thyroxine measurement. Blood was drawn 3 and 8 hours after gabapentin administration (10 mg/kg capsule orally once followed by 3 ml water). Gabapentin serum concentration was measured using liquid chromatography coupled to tandem mass spectrometry. Half-life was determined by calculating the rate of gabapentin elimination between the 3 hour and 8 hour time points. Comparison of half-life between the CKD and clinically healthy cats was performed with Mann-Whitney test and correlation between serum creatinine and gabapentin half-life was performed with Spearman Rank. Five apparently healthy and nine CKD cats (4 IRIS Stage 2, 5 IRIS Stage 3) completed the study. CKD cats had a median age of 15 years (range 5-18) and a median serum creatinine 2.6 mg/dL (2.4-3.3). Apparently healthy cats had a median age of 1.6 years (range 1-7) and a median serum creatinine 0.9 mg/dL (0.9-1.3). After administration of a single oral 10 mg/kg dose of gabapentin (median 10, range 9.6-10.3 mg/kg), CKD cats had a significantly longer median calculated half-life (13.1 hours, range 7.3-19.9) in comparison to normal cats (4.3 hours, range 3.9-6.9)(p = 0.001). Serum creatinine was significantly correlated with calculated half-life (p = 0.0002, r = 0.86). CKD significantly delays the clearance of gabapentin and this information should be taken into account when prescribing to these patients.
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