Would you rather inject yourself once a month or take a pill every day? Unless you're extremely needle-phobic, it's not an easy question to answer. There are advantages and disadvantages to both.

Biogen Idec (Nasdaq: BIIB) is hedging its bets, figuring there will be a market for both types of multiple sclerosis treatments. It's already produced positive phase 3 data for its oral BG-12 and yesterday released solid -- albeit far from perfect -- phase 2b data for its once-monthly daclizumab.

The drug's efficacy looks pretty good. Patients taking once-monthly daclizumab had an annualized relapse rate 50% to 54% depending on the dose compared with patients taking a placebo. That's on par with BG-12 and certainly better than Teva Pharmaceuticals' (Nasdaq: TEVA) laquinimod and its adjusted 21% reduction in the annualized relapse rate.

But the side-effect profile leaves something to be desired. Serious infections occurred in 2% of patients taking once-monthly daclizumab compared with 0% in placebo. That's not all that surprising, since the drug is designed to inhibit the immune system; Roche sells a version of daclizumab called Zenapax to treat organ-transplant patients.

The bigger worry might come from the 4% of patients whose liver enzyme levels were five times higher than normal, which is a good indicator that the drug might be damaging the liver. And since it's a monthly treatment, the drug will be in the system for quite awhile after doctors decide there's a problem.

Two patients taking once-monthly daclizumab died while in the study, although it wasn't clear the drug was the cause.

The mixed data is good enough for Biogen and its partner Abbott Labs (NYSE: ABT) to continue with the currently enrolling phase 3 trial, but not so great that investors should pencil in revenue from once-monthly daclizumab. The drug would certainly be more convenient than current multiple sclerosis treatments like Copaxone from Teva and Rebif from Pfizer (NYSE: PFE) and Merck KGaA, but we'll have to see data from a larger and longer trial to know whether the risk-reward profile is good enough to get past the Food and Drug Administration.

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