PERIOPERATIVE PROPHYLAXIS WITH PHENYTOIN - DOSAGE AND THERAPEUTIC PLASMA-LEVELS

Early postoperative epilepsy is a frequent complication of supratentor ial intracranial surgery. The lack of consensus on prophylaxis of earl y postoperative seizures with phenytoin (PHT) may be due to the differ ent dosages used in several studies, owing to inadequate therapeutic p lasma level. The aim of this study was to evaluate which dosage of PI- IT can maintain the therapeutic range in the early postoperative perio d. Twenty patients operated on for supratentorial neoplasms were rando mly allocated to receive, during the last hour of the surgical procedu re, loading doses of either 10 mg/kg (group A, n = 10) or 15 mg/kg (gr oup B, n = 10) of PHT. PHT infusion rate never exceeded 30 mg/min. Six hours after the loading dose, PHT maintenance treatment (250 mg, i.v. , every 8 hours) was started in all patients. PHT plasma levels were e valuated from the end of the intra-operative loading infusion up to 24 h. During the first six hours after the loading dose, phenytoin plasm a levels fell below the therapeutic range (10-20 mg/l) in 7 out of the 10 patients receiving 10 mg/kg, while in the patients treated with 15 mg/kg, PHT plasma levels were always in the therapeutic range (P less than or equal to 0.0001). PHT maintenance dose was sufficient to keep plasma levels within the therapeutic range in 8 patients in group A, and in all the patients in group B. It is concluded that a loading dos e of 15 mg/kg, followed by postoperative treatment, is necessary to gu arantee therapeutic plasma levels of phenytoin in the immediate postop erative period, when seizure risk is very high.