• Johannessen Landmark Cecilie C Department for Pharmacy and Biomedical Science, Oslo and Akershus University College, Norway; Department of Pharmacology, Oslo University H, Georg Beiske, Arton Baftiu, Margrete L Burns, and Svein I Johannessen.
• Department for Pharmacy and Biomedical Science, Oslo and Akershus University College, Norway; Department of Pharmacology, Oslo University Hospital, Oslo, Norway; National Center for Epilepsy, Oslo University Hospital, Sandvika, Norway. Electronic address: cecilie.landmark@hioa.no.
• Seizure. 2015 May 1; 28: 88-91.

PurposeGabapentin and pregabalin are antiepileptic drugs (AEDs) with epilepsy and neuropathic pain indications. The purpose of this study was to investigate pharmacokinetic variability of gabapentin and pregabalin and indications for therapeutic drug monitoring (TDM) in clinical practice with focus on gender aspects.MethodAnonymous data from routine TDM-service at the National Center for Epilepsy regarding serum concentration measurements of gabapentin and pregabalin, 2009-2013, were utilised. All included samples were drug-fasting in the morning at steady-state.ResultsIn total, 356 patients were included; gabapentin 189 (66% women), average age 53 years and pregabalin 167 (56% women), average age 50 years. For gabapentin, mean serum concentration/dose(C/D)-ratio was similar across genders. Only 13% of the patients had concentrations above the lower limit of the reference range (70-120 μmol/L), which indicates a need for reevaluation of the reference range. For pregabalin, the C/D-ratio in women (0.08±0.06) was 42% higher than in men (0.056±0.05; p<0.05). The pharmacokinetic variability (C/D-ratio) was >100-fold for both gabapentin and pregabalin. An indication of use (epilepsy/pain/other) was stated in only 26% of the cases (n=94). Epilepsy was assumed as indication when other AEDs were also measured (50% of patients). This was similar for both genders and for both AEDs. Indications for TDM were stated in 155 cases (44%) and were similar for gabapentin and pregabalin.ConclusionGabapentin and pregabalin are more used in women than in men, and routine use of TDM is most common in patients with epilepsy. Pharmacokinetic variability is extensive, highlighting a need for individualisation of therapy regardless of indication.Copyright © 2015 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.

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