Sister chromatid exchanges (SCE) were studied in lymphocyte cultures of 12 adult male epileptic patients on long-term monotherapy with phenytoin (PHT) and of matched controls. Significantly increased frequency of SCE was observed in the epileptic patients as a group and in almost all individuals, indicating a detectable chromosome damaging effect of PHT therapy on its human users.

The effect of carbamazepine (CBZ) on human chromosomes was studied in an effort to determine its mutagenic potential. Analysis of chromosome breakage, sister chromatid exchanges (SCE), and cell cycle studies were performed in peripheral lymphocyte cultures. The in vivo studies failed to detect any significant increase of chromosome aberrations or SCE or any slowing of the cell cycle. A significant dose-dependent increase in chromosome aberrations but not in SCE was observed in the in vitro analyses. No correlation was observed between chromosome breaks and SCE in either the in vivo or in vitro studies. The negative in vivo results indicate an absence of detectable chromosome-damaging effects of CBZ used in monotherapy in human subjects.