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Factors in Variability of Serial Gabapentin Concentrations in Elderly Patients with Epilepsy
Author(s) -
Conway Jeannine M.,
Eberly Lynn E.,
Collins Joseph F.,
Macias Flavia M.,
Ramsay R. Eugene,
Leppik Ilo E.,
Birnbaum Angela K.
Publication year - 2017
Publication title -
pharmacotherapy: the journal of human pharmacology and drug therapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.227
H-Index - 109
eISSN - 1875-9114
pISSN - 0277-0008
DOI - 10.1002/phar.2012
Subject(s) - gabapentin , coefficient of variation , medicine , creatinine , epilepsy , linear regression , body mass index , renal function , anesthesia , zoology , mathematics , statistics , alternative medicine , pathology , psychiatry , biology
Objectives To characterize and quantify the variability of serial gabapentin concentrations in elderly patients with epilepsy. Methods This study included 83 patients (age ≥ 60 yrs) from an 18‐center randomized double‐blind double‐dummy parallel study from the Veterans Affairs Cooperative 428 Study. All patients were taking 1500 mg/day gabapentin. Within‐person coefficient of variation ( CV ) in gabapentin concentrations, measured weekly to bimonthly for up to 52 weeks, then quarterly, was computed. Impact of patient characteristics on gabapentin concentrations (linear mixed model) and CV (linear regression) were estimated. Results A total of 482 gabapentin concentration measurements were available for analysis. Gabapentin concentrations and intrapatient CV s ranged from 0.5 to 22.6 μg/ml (mean 7.9 μg/ml, standard deviation [ SD ] 4.1 μg/ml) and 2% to 79% (mean 27.9%, SD 15.3%), respectively, across all visits. Intrapatient CV was higher by 7.3% for those with a body mass index of ≥ 30 kg/m 2 (coefficient = 7.3, p=0.04). CV s were on average 0.5% higher for each 1‐unit higher CV in creatinine clearance (coefficient = 0.5, p=0.03) and 1.2% higher for each 1‐hour longer mean time after dose (coefficient = 1.2, p=0.04). Conclusions Substantial intrapatient variability in serial gabapentin concentration was noted in elderly patients with epilepsy. Creatinine clearance, time of sampling relative to dose, and obesity were found to be positively associated with variability.