Snapshot A 45-year-old man presents to his primary care physician for discoloration of his toenails. He reports that he has had this issue for the past few months. He denies any itching or pain associated with this toenail. On physical exam, his right big toenail is thickened with yellow discoloration. There are scale and fissures affecting the surrounding skin. Skin scrapings of the active edge mixed with potassium hydroxide reveal septated hyphae and spores. He is prescribed an oral medication that is particularly effective as it deposits in the nails (onychomycosis). Introduction Drugs griseofulvin Mechanism of action fungistatic binds to microtubules and disrupts mitosis in fungi the drug deposits in tissue containing keratin (nails) and is thus particularly effective in dermatophytic infections Clinical use onychomycosis dermatophytic infections Adverse effects photosensitivity gastrointestinal upset headaches teratogenic disulfiram-like reaction ↑ cytochrome P-450