title: Therapeutic drug monitoring of mexiletine at a large academic medical center.
abstract: BACKGROUND
  The therapeutic trough range for mexiletine (0.8-2 mcg/mL) was largely established in the setting of arrhythmia prophylaxis following myocardial infarction.
  
  
  OBJECTIVE
  Describe the usage patterns of serum mexiletine concentrations and the impact of these concentrations on mexiletine dosing in modern practice for ventricular arrhythmia treatment.
  
  
  METHODS
  A single-center, retrospective analysis was conducted using the electronic medical record to identify serum mexiletine concentrations drawn between December 2004 and December 2014. The primary endpoint was the incidence of mexiletine concentrations drawn as troughs. Secondary outcomes included the incidence of mexiletine concentrations that prompted a dose change, association between adverse events and elevated concentrations, and association between baseline characteristics and mexiletine concentrations.
  
  
  RESULTS
  A total of 237 individual concentrations were included for analysis with 109 (46.0%) drawn appropriately as trough concentrations. Only 31 (13.1%) of the 237 concentrations drawn prompted a dose change. Mexiletine was primarily used for the treatment of ventricular arrhythmias (96.2%), and 108 (45.6%) concentrations were drawn in an effort to assess efficacy. The median concentration was statistically different between patients with and without an adverse event (0.8 vs 0.7 mcg/mL, respectively; p = 0.017), but may not represent a clinical significance. Patients with hepatic dysfunction had higher median concentrations compared to those without hepatic dysfunction (1.30 vs 1.07 mcg/mL; p = 0.01).
  
  
  CONCLUSIONS
  Mexiletine concentrations are often drawn at inappropriate times and seldom influence a dose change. This study suggests that routine monitoring of mexiletine concentrations may not be necessary; however, therapeutic drug monitoring may be considered in patients with hepatic dysfunction or to confirm mexiletine absorption in patients where this represents a concern.
authors.affiliation: Department of Pharmacy, Mayo Clinic, Rochester, MN, USA.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Nei
authors.affiliation: Department of Pharmacy, Mayo Clinic, Rochester, MN, USA.
authors.forename: Ilya M
authors.initials: IM
authors.lastname: Danelich
authors.affiliation: Department of Pharmacy, Mayo Clinic, Rochester, MN, USA.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Lose
authors.affiliation: Department of Pharmacy, Mayo Clinic, Rochester, MN, USA.
authors.forename: Lydia Yuk Ting
authors.initials: LY
authors.lastname: Leung
authors.affiliation: Division of Cardiology, Department of Medicine, Mayo Clinic, Rochester, MN, USA; Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN, USA.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Asirvatham
authors.affiliation: Division of Cardiology, Department of Medicine, Mayo Clinic, Rochester, MN, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: McLeod
keywords: Cardiovascular; antiarrhythmics; drug monitoring; therapeutic monitoring