Changes in plasma phenytoin level following craniotomy.
Yeh JS., Dhir JS., Green AL., Bodiwala D., Brydon HL.
Phenytoin is often used to prevent postcraniotomy seizures, but is not always effective. We investigate changes in plasma phenytoin level ([phenytoin]) following craniotomy. The [phenytoin] in 28 patients who were receiving phenytoin (oral/ intravenous) and undergoing a craniotomy were prospectively measured 24 h preoperatively, immediately pre- and postcraniotomy, 24 and 48 h postoperatively. Factors examined included patients' age, sex, pathology, preoperative [phenytoin], operative duration and blood loss. Fifteen patients had [phenytoin] concentrations outside the therapeutic range. Twenty-five patients experienced a decrease in [phenytoin] immediately postcraniotomy: pre-, post- and 24 h postcraniotomy mean [phenytoin] were 13.4, 10.0 and 12.9 mg/l, respectively. Preoperative [phenytoin], operative duration and blood loss had significant correlation with the decrease in [phenytoin] (p < 0.05). In conclusion, < 50% of the patients had therapeutic preoperative [phenytoin]. In most patients, [phenytoin] decreases by 26% after craniotomy and returns to preoperative level within 24 h. These may contribute to early postoperative seizure development.