Cross-reactive skin eruption with both carbamazepine and oxcarbazepine.

Oxcarbazepine (OCBZ), a 10-keto derivative of carbamazepine (CBZ) has been reported to have a similar range of efficacy and fewer unwanted effects than CBZ since it is a prodrug for the monohydroxy derivative (MHD). A cross-reactivity of only 1 in 4 has been reported between OCBZ and CBZ. For these reasons, we tried OCBZ with 3 consecutive patients with poorly controlled epilepsy who had had a therapeutic response to CBZ but in whom CBZ was discontinued because of serious skin reaction. Each patient had a similar skin response after exposure to only 600-900 mg OCBZ, which suggests a need to practice caution when substituting OCBZ for CBZ in patients known to have serious skin reaction to CBZ.