Drug Week via NewsEdge Corporation :
2007 NOV 23 - (NewsRx.com) -- Data detailed in 'Population pharmacokinetics of valproic Acid concentrations in elderly nursing home residents' have been presented (see also Pharmacokinetics). "The objective of this study was to identify factors that affect valproic acid (VPA) apparent clearance (CL/F) in elderly nursing home residents. Inclusion criteria included residency in a nursing home for at least 2 months, aged 65 years or older, a stable dosing regimen of VPA for at least 4 weeks, VPA concentration, and complete dosing information," scientists writing in the journal Therapeutic Drug Monitoring report.
"CL/F was analyzed by a nonlinear mixed effects model. A one-compartment model with first-order absorption and elimination was used. Both volume and absorption rate constant were fixed (14 L and 1 hr, respectively). Covariates were tested by forward inclusion and backward elimination. Interindividual variability in clearance was estimated using an exponential error model and expressed as a coefficient of variation. Residual error was estimated using a combined additive and constant coefficient of variation error model. The study consisted of 405 observations from 146 (52 men, 94 women) elderly nursing home residents. CL/F was not affected by age or weight. The population CL/F was 0.843 L/hr. CL/F was 1) 27% lower in female residents; 2) 41% greater when the resident was on concomitant metabolic inducers carbamazepine or phenytoin cotherapy; and 3) 25% greater when the syrup formulation was used. Variability in CL/F was 32.9%. Coefficient of variation and standard deviation of the residual error were 18.2% and 10.6 mg/L, respectively. The increased CL/F in patients taking VPA syrup may be the result of a decreased bioavailability (F) rather than an increased CL that could be associated with pathology requiring use of the syrup rather than an inherent property of the drug formulation," wrote A.K. Birnbaum and colleagues, University of Minnesota.
The researchers concluded: "The results from this study may be useful for individualizing dose regimens in the nursing home population based on patient-specific factors."
Birnbaum and colleagues published their study in Therapeutic Drug Monitoring (Population pharmacokinetics of valproic Acid concentrations in elderly nursing home residents. Therapeutic Drug Monitoring, 2007;29(5):571-5).
Additional information can be obtained by contacting A.K. Birnbaum, University of Minnesota, Experimental and Clinical Pharmacology, Minneapolis, Minnesota 55455 USA..
The publisher of the journal Therapeutic Drug Monitoring can be contacted at: Lippincott Williams & Wilkins, 530 Walnut St., Philadelphia, PA 19106-3621, USA.
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