Which of the following drugs is most commonly associated with drug-induced gingival enlargement?

Phenytoin (Dilantin), an anticonvulsant medication, is the classic drug associated with drug-induced gingival enlargement (formerly called gingival hyperplasia). It stimulates gingival fibroblasts to produce excess collagen, resulting in overgrowth of gingival tissue, particularly in the anterior region. The severity is exacerbated by poor oral hygiene. Other drugs known to cause gingival enlargement include calcium channel blockers (e.g., nifedipine, amlodipine) and immunosuppressants (e.g., cyclosporine). Metformin, amoxicillin, and ibuprofen do not cause gingival enlargement.