Optimization of phenytoin therapy in adults with epilepsy in the Western Cape, South Africa

Objective: To assess the extent to which adults with epilepsy were optimize d and individualized on phenytoin monotherapy in the Western Cape, South Af rica and to estimate the average optimized dose and serum phenytoin concent ration, and the therapeutic range for this patient group. Methods: Patients were considered to be optimized on phenytoin if they were seizure-free or the best compromise was achieved between seizure reduction and side-effects. Results: 538 (233 black and 305 coloured) adult people with epilepsy were t reated at nine epilepsy clinics as outpatients. Of these patients, 332 (226 male and 106 female, 149 black and 183 coloured) were included in the data analysis as they were considered to have reliable phenytoin levels. Phenyt oin doses and steady-state serum concentrations were predicted using the Mi chaelis-Menten equation. Patients attended a clinical pharmacokinetic servi ce for 7.7 +/- 5.3 (range 1-22) months. The average optimized dose was 305. 8 (range 100-500) mg/day and the average optimized level was 62.7 +/- 23.9 (range 15-133) mu mol/l. Most patients (61.9%) were optimized in the therap eutic range 40-79 mu mol/l; 21.1% were optimized above and 17% below this r ange. In 1.6% of patients serum concentrations above 120 mu mol/l were requ ired. Dosage adjustments were made in 47.0% of patients, increased in 31.9% and reduced in 15.1%. Conclusion: These findings indicate that many patients (47%) attending outp atient clinics were not optimized on phenytoin therapy.