Affiliation:
1. Department of Neurology University Hospital Dubrava Zagreb Croatia
2. Faculty of Dental Medicine and Health Josip Juraj Strossmayer University of Osijek Osijek Croatia
3. Department of Pharmacology Zagreb University School of Medicine Zagreb Croatia
4. Croatian Agency for Medicinal Products and Medical Devices Zagreb Croatia
5. Analytical Toxicology and Pharmacology Division, Department of Laboratory Diagnostics University Hospital Centre Zagreb Zagreb Croatia
6. Division of Pharmacogenomics and Therapy Individualization, Department of Laboratory Diagnostics University Hospital Centre Zagreb Zagreb Croatia
Abstract
AbstractBackgroundValproate inhibits clearance of lamotrigine and greatly increases its concentrations. We assessed whether this effect was moderated by a polymorphism (ABCG2 c.421C>A) of the breast cancer resistance protein.MethodsIn two consecutive independent studies in adults with epilepsy on lamotrigine monotherapy or cotreated with valproate: (i) Exposure to valproate was considered treatment, (ii) dose‐adjusted lamotrigine troughs at steady state were the outcome, and (iii) ABCG2 c.421C>A genotype (wild‐type [wt] homozygosity or variant carriage) was the tested moderator. We used entropy balancing (primary analysis) and exact/optimal full matching (secondary analysis) to control for confounding, including polymorphisms (and linked polymorphisms) suggested to affect exposure to lamotrigine (UGT1A4*3 c.142T>G, rs2011425; UGT2B7–161C>T, rs7668258; ABCB1 1236C>T, rs1128503) to generate frequentist and Bayesian estimates of valproate effects (geometric means ratios [GMR]).ResultsThe two studies yielded consistent results (replicated); hence, we analyzed combined data (total N = 471, 140 treated, 331 controls, 378 ABCG2 c.421C>A wt subjects, 93 variant carriers). Primary analysis: in variant carriers, valproate effect (GMR) on lamotrigine (treated, n = 21 vs. controls, n = 72) was around 60% higher than in wt subjects (treated, n = 119 vs. controls, n = 259)—ratio of GMRs 1.61 (95%CI 1.23–2.11) (frequentist) and 1.63 (95%CrI 1.26–2.10) (Bayes). Similar differences in valproate effects between variant carriers and wt subjects were found in the secondary analysis (valproate troughs up to 364 μmol/L vs. no valproate; or valproate ≥364 μmol/L vs. no valproate). Susceptibility of the estimates to unmeasured confounding was low.ConclusionData suggest that polymorphism rs2231142 moderates the effect of valproate on exposure to lamotrigine.
Subject
Pharmacology (medical),Pharmacology