A 45-year-old man has distal subungual onychomycosis of all toenails confirmed on KOH and culture as Trichophyton rubrum. He is started on oral terbinafine 250 mg daily. What is the recommended duration of continuous therapy for toenail disease?
- A 2 weeks
- B 6 weeks
- C 12 weeks ✓
- D 24 weeks
Correct answer: C. 12 weeks
Explanation
Terbinafine 250 mg daily is given continuously for 12 weeks for toenail onychomycosis and only 6 weeks for fingernail disease, because the toenail grows far more slowly and takes about 12 months to replace completely. Two weeks would be a pulse schedule concept for other drugs, and 24 weeks is not standard. Cure assessment is delayed because the drug remains concentrated in the nail plate after stopping.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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