title: Possible drug-drug interaction between quetiapine and lamotrigine--evidence from a Swedish TDM database.
abstract: OBJECTIVE
  The aim of the present study was to investigate a previously proposed interaction between quetiapine and lamotrigine resulting in reduced serum quetiapine concentrations.
  
  
  METHODS
  Data on 402 patients subjected to analysis of quetiapine concentration in serum were extracted from a routine therapeutic drug monitoring database. Among these patients, those concomitantly treated with lamotrigine (n= 22) were identified and matched with 22 controls receiving quetiapine while unexposed to lamotrigine. The dose-corrected quetiapine concentrations (C : D ratios) in the two groups were compared in both paired and unpaired analyses.
  
  
  RESULTS
  Patients co-treated with lamotrigine had a lower mean C : D ratio (0.71, 95% CI 0.46, 0.97) compared with controls (1.64, 95% CI 1.00, 2.28). Dose-corrected quetiapine concentrations were 58% lower in patients co-medicated with lamotrigine.
  
  
  CONCLUSIONS
  This study indicates that lamotrigine exposure is associated with substantially reduced serum concentrations of quetiapine, possibly due to induced glucuronidation. These findings need to be confirmed in experimental studies.
authors.affiliation: Department of Laboratory Medicine, Division of Clinical Pharmacology, Karolinska University Hospital, Huddinge, Karolinska Institutet, 141 86 Stockholm, Sweden. marine.andersson@karolinska.se
authors.forename: Marine L
authors.initials: ML
authors.lastname: Andersson
authors.forename: Linda
authors.initials: L
authors.lastname: Björkhem-Bergman
authors.forename: Jonatan D
authors.initials: JD
authors.lastname: Lindh
mesh_terms: D000293:Adolescent; D000328:Adult; D000927:Anticonvulsants / Q000493:pharmacokinetics*; D014150:Antipsychotic Agents / Q000493:pharmacokinetics*; D016022:Case-Control Studies; D003987:Dibenzothiazepines / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D006801:Humans; D000077213:Lamotrigine; D008297:Male; D008875:Middle Aged; D000069348:Quetiapine Fumarate; D013548:Sweden; D014227:Triazines / Q000493:pharmacokinetics*; D055815:Young Adult
chemical_list: D000927:Anticonvulsants; D014150:Antipsychotic Agents; D003987:Dibenzothiazepines; D014227:Triazines; D000069348:Quetiapine Fumarate; D000077213:Lamotrigine