Phenytoin sensitivity of fibroblasts as the basis for susceptibility to gingival enlargement.

A side effect of long-term administration of the anti-epileptic drug phenytoin is overgrowth of the connective tissues surrounding the teeth. In this in vitro study of protein and collagen synthesis by diploid fibroblasts from 17 nonepileptic young persons with healthy gingivae, only seven strains of cells responded to phenytoin in culture medium. Because not all phenytoin-treated individuals develop gingival overgrowth, we suggest that susceptibility is predicated upon the presence of a (genetically determined) phenytoin-sensitive subpopulation of gingival fibroblasts. The concept of the participation of sensitive cell subpopulations in other connective tissue disorders is supported by these findings.