COMMENTARY

Is Testing Needed Before Treating Onychomycosis With Terbinafine?

Graeme M. Lipper, MD

Disclosures

April 19, 2016

Viewpoint

Is pretreatment confirmation of onychomycosis before prescribing oral terbinafine therapy no longer necessary? Mikailov and colleagues' thought-provoking analysis certainly supports this conclusion, with some important caveats.

Terbinafine, while highly effective against dermatophyte infections, will not clear onychomycosis caused by a yeast or saprophyte; oral azoles such as itraconazole would be the appropriate treatment in such cases, which are best differentiated from dermatophytes through fungal culture. Patients at greater risk for terbinafine-induced hepatotoxicity (eg, history of hepatitis, alcohol consumption, taking potentially hepatotoxic medications such as statins) may also benefit from confirmatory testing prior to starting terbinafine; Mikailov and colleagues' cost analysis does not "carve out" this higher-risk subset. Nevertheless, the risk for clinically apparent liver injury from oral terbinafine has been greatly exaggerated and occurs in as few as 1 in 50,000 to 100,000 treatments, with even rarer instances of durable clinical sequelae.[4]

One thing seems clear though: As long as topical antifungal agents such as efinaconazole remain astronomically expensive, there will still be a cost-saving role for confirmatory testing to "nail down" the diagnosis of onychomycosis first.

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