Final answer:
Terbinafine, belonging to the allylamine class, is the antifungal drug primarily used for the treatment of dermatophyte infections and is commonly prescribed in both topical and oral forms.
Step-by-step explanation:
The antifungal drug that is used primarily for the treatment of dermatophyte infections is terbinafine. Terbinafine is part of the allylamine class of antifungals, which inhibits an early step in ergosterol biosynthesis, crucial to fungal cell membrane structure. Unlike other antifungals that have a broader spectrum of action, terbinafine is particularly effective against dermatophytes and is commonly prescribed topically for skin infections such as athlete's foot (tinea pedis), ringworm (tinea corporis), and jock itch (tinea cruris). Terbinafine is also used in an oral form for more serious infections like onychomycosis, which affects fingernails and toenails, though it has a rare side effect of hepatotoxicity.
Other antifungals like griseofulvin, miconazole, and clotrimazole are also used to treat dermatophyte infections, but they have broader indications and are not used exclusively for dermatophytes. Griseofulvin, for example, was one of the first antifungals and is administered orally for various dermatophytic skin infections. However, its usage has declined due to associated hepatotoxicity.