Incidence, Presentation, and Risk Factors for Sodium Valproate-Associated Hyperammonemia in Neurosurgical Patients: A Prospective, Observational Study

OBJECTIVE: Sodium valproate (VPA) is a commonly prescribed antiepileptic drug (AED) in daily neurosurgical practice. However, the incidence of VPA-associated hyperammonemia (VAH) and its life-threatening consequence, VPA-induced hyperammonemic encephalopathy (VHE), in neurosurgical patients is unknown. We determined the incidence, clinical presentation, and risk factors for VAH. METHODS: This prospective cohort study was performed on adult neurosurgical patients prescribed VPA for at least a week over a 22-month period. Blood tests for ammonia, VPA, and liver function were performed at the time of recruitment. The primary end point was VAH. Secondary end points were VHE and liver dysfunction. RESULTS: In total, 252 patients were recruited. The commonest disease etiology was brain tumors (27%, 69), followed by aneurysmal subarachnoid hemorrhage (SAH; 26%, 65). VPA was prescribed for primary seizure prophylaxis in 110 patients (44%). The mean daily dose was 1148 mg for a mean duration of 48 months. The mean serum VPA level was 417 mu mol/L. In total, 92 patients (37%) were prescribed an additional AED, the most common being phenytoin (65%, 60/92). The mean serum ammonia level was 47 Imola. In total, 28% (71/252) of patients had VAH and only 0.7% had VHE. Independent factors were aneurysmal SAH (adjusted odds ratio [aOR] 2.1; 95% confidence interval [CI] 1.1-4.2), concomitant phenytoin (aOR 1.9; 95% CI 1.0-3.5), and phenobarbital (aOR 4.6; 95% CI 1.1-20.0). No associations with VPA dose, duration, serum levels, and liver function were observed. CONCLUSIONS: Although VAH is common among neurosurgical patients, VHE is rare. Patients with aneurysmal SAH or on concomitant enzyme-inducing AEDs are at risk. Clinicians should be vigilant for VHE symptoms in these patients.