Loss of seizure control associated with generic substitution of carbamazepine

We report two cases of lost seizure control associated with the generic substitution of carbamazepine, review pertinent literature, and discuss the impact of this substitution on patient care.

Case studies, abstracts, and research publications identified in MEDLINE and bibliographic review.

One author reviewed cases supplied by the other authors and abstracted information from published literature sources.

The first case describes a 15-year-old boy who received valproic acid and carbamazepine for partial seizures. A change in government program policies caused him to receive generic carbamazepine. This resulted in loss of seizure control and a decrease in his serum carbamazepine concentration from 12.4 to 6.7 micrograms/mL. When his carbamazepine concentration returned to previous levels, seizure control was not reestablished. A second case involves a 21-year-old woman who substituted generic carbamazepine because of financial problems. After being seizure-free for at least five years on phenobarbital and carbamazepine, she experienced seizures related to the product change. Her carbamazepine concentration decreased from 11.8 to 8.5 micrograms/mL; she also became pregnant at that time. Seizure control was not reestablished. At least three other studies do not support these observations, but the tightly controlled conditions in these studies may not have simulated actual clinical practice.

When generic substitution of carbamazepine is required, serum concentrations should be carefully monitored. The extra care required may negate the financial advantages of the substitution.