The nice thing about developing a drug for a disease without any other treatment options: You've got no competition.

The bad thing about developing a drug for a disease without any other treatment options: You've got to find the patients.

AVANIR Pharmaceuticals's (Nasdaq: AVNR) Nuedexta is off to a slow start after being approved to treat patients with pseudobulbar affect, a disease in which patients with underlying neurological diseases have trouble controlling their emotions. The company sold just $505,000 worth of the drug during the first three months of the year.

Granted, it was only actively promoting the drug for eight weeks, but the ramp up doesn't seem all that steep. Prescription data for April only puts the run rate at about $5.5 million a year.

New orphan indications can be lucrative, but the problem for AVANIR is that pseudobulbar affect isn't life threatening. Uncontrolled crying or laughing is certainly embarrassing, but there's no immediate need to treat the patient like there is for the orphan diseases treated with drugs such as BioMarin Pharmaceuticals's (Nasdaq: BMRN) Naglazyme, Alexion Pharmaceutical's (Nasdaq: ALXN) Soliris, and Viropharma's (Nasdaq: VPHM) Cinryze.

Doctors are likely taking a wait-and-see approach: prescribing it to one patient, seeing how it works, and then prescribing it for additional patients if the drug works.

The important number to watch then is the number of prescriptions being refilled. In April, the prescription data showed about 300 repeat prescriptions compared with about 850 total prescriptions in March. Either there are a lot of patients getting more than a one-month supply, which is unlikely, or they're not refilling their prescriptions.

I wouldn't write off Nuedexta just yet -- third-party prescription data shouldn't be taken as exact, and it's only one data point -- but it's certainly a trend investors shouldn't be laughing about.

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