Anacor Readies Results From Pivotal Study of Toenail Fungus Drug

PALO ALTO, Calif. ( TheStreet) -- Let's talk toenail fungus. I know, not exactly the most appealing topic but 36 million Americans suffer from onychomycosis, the disease's scientific name, making this a potential $250-300 million market opportunity for the tiny drug maker Anacor Pharmaceuticals ( ANAC).

Anacor will be announcing results any day from the first of two phase III studies of tavaborole, a topical, once-daily treatment for toenail fungus. The studies enrolled 600 toenail fungus sufferers each, randomized to one year of treatment with tavaborole or the drug's alcohol-based delivery vehicle alone (essentially the placebo.)

The study's primary endpoint measures "complete cure" -- defined as the percentage of patients in each arm who are fungus free (mycologic cure) plus have completely clear nails after 52 weeks of treatment.

This is not the endpoint used in Anacor's phase II studies, which makes it difficult to predict the results from the ongoing phase III studies.

Tavaborole's previous six-month mycologic cure rates from the phase II studies are in the 50-60% range so meeting this portion of the "complete cure" threshold shouldn't be too problematic. One thing to watch and worry about: One 12-month patient cohort from the phase II studies yielded a paltry 22% mycologic cure rate. Outlier or worrisome signal of falling efficacy over time?

It's harder to forecast how well the drug will grow new, clear nail because the phase II studies were shorter (just six months duration) and measured percentage of patients with 2 millimeters or more of new nail growth (less than a completely clear nail.)

In the largest phase II study conducted, tavaborole at 5% concentration (the phase III dose) yielded a 26% response rate compared to 14% for placebo.

Tavaborole must beat placebo in order for the phase III studies to be successful but investors will also be comparing the drug's efficacy against efinaconazole, an experimental toenail fungus drug from Valeant Pharmaceuticals ( VRX), currently under FDA review. Efinaconazole's drug approval decision date is May 24.

In two phase III studies recently published, efinaconazole demonstrated complete cure rates of 17.8% and 15.2% compared to placebo rates of 3.3% and 5.5%. Valeant used the same definition of complete cure as Anacor is using for its phase III studies.

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