EVALUATION OF A BAYESIAN PHARMACOKINETIC PROGRAM FOR PHENYTOIN CONCENTRATION PREDICTIONS IN OUTPATIENT POPULATION

The present work evaluates the performances of a Bayesian program (PKS ) for phenytoin concentration predictions in an outpatient population. The retrospective study involved 19 epileptic adults receiving oral p henytoin. The program was used to predict estimated serum concentratio ns from 0, 1, 2 or 3 feedback concentrations. Measurements of predicti on bias (ME) decreased as soon as one steady-state concentration (Css) was used for estimations. Precision (MAE) was significantly improved with I Css and was even better and stable with 2 and 3 Css. Likewise, RMSE (composite of bias and precision) regularly decreased when the nu mber of Css used increased. On a clinical way, 12% of the estimations were unacceptable (prediction error > 5 mg/l) with 1 Css and less than 3% with 2 or 3 Css. This number of rejected estimations increased to 45% when no feedback concentration was used. Besides, the program was able to predict important rises of serum levels in spite of relative l ow increase of the dose when 1 Css at least was known. Thus, the pheny toin dosing program has acceptable performances when at least 1 Css is known, and represents a potential tool to assist the clinician in the particular condition of outpatient population.