Acute hyperammonemic coma with chronic valproic acid therapy

OBJECTIVE: To report a case of dose-related hyperammonemic coma without liver failure in a patient receiving chronic valproate therapy. CASE SUMMARY: A 56-year-old woman with poorly controlled epilepsy, receiving valproate at subtherapeutic levels for 6 years, developed a life-threatening hyperammonemic coma following a moderate dosage increase. DISCUSSION: Hyperammonemic coma without associated liver failure is an extremely rare complication of valproate therapy, described primarily in patients with inborn errors of metabolism and occurring idiosyncratically during initial stages of therapy. In our case, family history was suggestive of an X-linked disorder, raising the possibility that our patient may have been an asymptomatic carrier of a urea cycle enzyme deficiency unmasked by valproate therapy. To our knowledge, as of October 24, 2005, only one prior case of hyperammonernic coma in the context of chronic valproate monotherapy has been described. Application of the Naranjo probability scale score suggests that a causal relationship between valproic acid and hyperammonernic coma was probable. CONCLUSIONS: The widespread use of valproic acid emphasizes the need to maintain a high degree of suspicion with respect to this rare but potentially fatal adverse effect at all times, regardless of therapy duration.