Decrease in serum valproic acid levels during treatment with ertapenem.

OBJECTIVE

A possible interaction between valproic acid and ertapenem resulting in reduced serum valproic acid levels in two patients is reported.

CONCLUSIONS

In the first case, a 47-year-old woman was brought to the emergency department (ED) with fever, pain, redness, swelling, and local heat in the tissue around her tracheostomy tube and left foot. One month prior she was hospitalized with pneumonia and had a generalized tonic-clonic seizure. She was given teicoplanin and amoxicillin-clavulanate potassium as empirical therapy for cellulitis. On day 3, the patient developed a fever. Amoxicillin-clavulanate potassium was discontinued and replaced by i.v. ertapenem. On day 5, due to a suspected drug-induced fever, carbamazepine was discontinued, and oral valproate sodium was initiated. On day 16, the patient was afebrile, so ertapenem was discontinued. Her serum valproic acid concentration was <1 mg/L, but seizures did not recur. Three days after ertapenem was discontinued, her serum valproic acid concentration increased to 33.6 mg/L. In the second case, a 72-year-old woman was brought to the ED after a sudden loss of consciousness and convulsive seizure. The patient was diagnosed with status epilepticus and admitted to the intensive care unit. A urine culture revealed Pseudomonas aeruginosa, and she was given cefpirome and valproate sodium. On day 15, cefpirome was replaced with ertapenem. On day 21, she had a seizure, and her serum valproic acid levels was found to be <1 mg/L. Ertapenem was discontinued after 14 days. Her serum valproic acid levels continued to increase until discharge on day 42.

CONCLUSIONS

After initiation of ertapenem, decreased serum valproic acid levels were observed in two patients.