title: Variability of carbamazepine and valproate concentrations in elderly nursing home residents.
abstract: OBJECTIVE
  Measuring antiepileptic drug (AED) concentrations is common practice in nursing homes. Phenytoin (PHT) concentrations fluctuate substantially in many nursing home residents under constant dose conditions; however, the stability of other AED concentrations has not been studied. We investigated the variability of carbamazepine (CBZ) and valproate (VPA) concentrations under constant dose conditions in US nursing home residents.
  
  
  METHODS
  A database of elderly persons (≥65 years) in 119 nursing homes throughout the US was reviewed for residents with at least one measurement of total PHT, CBZ or VPA. Inclusion criteria for this study were three or more serum concentration measurements while on the same dose of CBZ or VPA, a two-month minimum stay, and no interfering co-medications (inducers or inhibitors). Enrollment occurred over a 2-year period. Data were collected on residents for a minimum of 6 months.
  
  
  RESULTS
  Of the 593 residents identified, 245 had CBZ or VPA concentrations measured and 44 (18%) met inclusion criteria (22 on CBZ and 22 VPA). Some subjects had little variability in AED concentrations, others had large fluctuations. Total CBZ concentrations within individuals varied as little as 0mg/L to as much as 6.3mg/L and total VPA concentrations as little as 10.0mg/L to as much as 77.6mg/L.
  
  
  CONCLUSIONS
  The variability of PHT, CBZ, and VPA concentrations in many but not all nursing home residents implies that a re-evaluation of the role of AED concentration measurements in the management of patients is needed. Strategies for use and interpretation of AED concentration measurements need to be reevaluated.
authors.affiliation: Department of Experimental & Clinical Pharmacology, College of Pharmacy, 717 Delaware St. SE, Minneapolis, MN 55414, USA. birnb002@umn.edu
authors.forename: Angela K
authors.initials: AK
authors.lastname: Birnbaum
authors.forename: Jeannine M
authors.initials: JM
authors.lastname: Conway
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Strege
authors.forename: Ilo E
authors.initials: IE
authors.lastname: Leppik
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000927:Anticonvulsants / Q000097:blood*; D002220:Carbamazepine / Q000097:blood*; D003627:Data Interpretation, Statistical; D016208:Databases, Factual; D005260:Female; D006801:Humans; D008297:Male; D009735:Nursing Homes; D010361:Patients; D010672:Phenytoin / Q000097:blood; D012640:Seizures / Q000188:drug therapy; D014635:Valproic Acid / Q000097:blood*
chemical_list: D000927:Anticonvulsants; D002220:Carbamazepine; D014635:Valproic Acid; D010672:Phenytoin