Competitor? No. Worrisome? Yes.

Regeneron Pharmaceuticals (NAS: REGN) traded down more than 12% today after privately held Ophthotech released data on its macular degeneration drug. Funny thing is, Ophthotech's drug, Fovista, won't compete directly with Regeneron's Eylea. The two drugs work through different mechanisms that seem to complement each other.

In Ophthotech's phase 2b trial, Fovista plus Roche's (OTC: RHHBY) Lucentis worked better than Lucentis alone. After 24 weeks of treatment, patients receiving Fovista and Lucentis could see an additional 10.6 letters on the eye chart, compared with a 6.5-letter gain for patients receiving Lucentis alone.

Lucentis and Eylea are fairly similar drugs; both work by blocking a protein called VEGF that promotes the growth of blood capillaries, a hallmark of the "wet" version of macular degeneration. There's good reason to think that Eylea should work with Fovista, which blocks blood vessels through a different protein called PDGF-B.

So then why is Regeneron trading down today? Part of the reason could have to do with dosing. Eylea's main benefit over Lucentis is that it can be dosed every other month, while Lucentis has to be dosed monthly. Less frequent dosing is always a plus; think Amylin Pharmaceuticals' (NAS: AMLN) once-weekly Bydureon versus once-daily Victoza from Novo Nordisk (NYS: NVO) or Johnson & Johnson's (NYS: JNJ) once-monthly Invega Sustenna over other more-frequently dosed antipsychotics. And the convenience factor goes double for a drug that has to be injected in the eye in elderly patients who may not be able to drive themselves into the doctor's office because of vision problems.

In Ophthotech's trial, Fovista was given monthly, which would negate the dosing benefit of Eylea. Of course, it's possible that Fovista would work on Eylea's less-frequent dosing schedule; Ophthotech would just need to run a trial to find out.

But depending on the goals of Ophthotech's backers, the start-up might not even be around long enough to test Fovista with Eylea. With solid phase 2 data, Ophthotech is in a good position to be acquired, the preferred route for venture capital exits these days. The two most obvious suitors would be Regeneron and Roche, with the latter obviously having the upper hand in a bidding war because of its much larger size. Assuming it didn't run into antitrust issues, Roche's owning Fovista would delay a trial testing an Eylea-Fovista combination until Regeneron could get a hold of the drug after Fovista's approval.

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