Asymptomatic hyperammonemia in patients receiving valproic acid.

Area of Science:

• Neurology
• Clinical Pharmacology

Background:

• Valproic acid is a widely used anticonvulsant medication.
• Hyperammonemia is a potential side effect of valproic acid therapy.
• The clinical significance of hyperammonemia in asymptomatic patients on valproic acid is not well-established.

Purpose of the Study:

• To investigate the incidence of hyperammonemia in asymptomatic patients undergoing valproic acid treatment.
• To compare ammonia levels in patients on valproic acid versus other anticonvulsants.
• To assess the tolerability and implications of elevated ammonia levels in this patient group.

Main Methods:

• Plasma ammonia concentrations were measured in 55 patients receiving valproic acid.
• A control group of 12 patients on other anticonvulsants was included for comparison.
• Specific attention was paid to patients on combination therapy with phenytoin or phenobarbital.

Main Results:

• Twenty-nine out of 55 patients (52.7%) on valproic acid exhibited elevated plasma ammonia (NH3) levels.
• No control patients showed elevated ammonia levels.
• Elevated ammonia levels were observed in 10/11 patients on valproic acid and phenytoin, and 5/6 patients on valproic acid and phenobarbital.
• The highest observed ammonia level was 140 mumole/L and was well-tolerated.

Conclusions:

• Hyperammonemia is a frequent finding in asymptomatic patients treated with valproic acid.
• Elevated ammonia levels associated with valproic acid therapy, even in combination, appear to be well-tolerated.
• Hyperammonemia alone should not be considered a reason to reduce or discontinue valproic acid treatment.