Mark your calendars, biotech investors. Two obesity drugs are up for review by Food and Drug Administration advisory panels in the coming months.

Both VIVUS' (Nasdaq: VVUS) Qnexa and Arena Pharmaceuticals' (Nasdaq: ARNA) lorcaserin were turned down by the FDA in October 2010. But the companies addressed safety concerns and are headed back in front of advisory panels.

VIVUS will go in front of the firing squad on Feb. 22. Arena expects its meeting to be held in the second quarter.

It's a little unusual for the FDA to schedule an advisory panel to review a second attempt at approval. Usually the FDA feels confident that they can make a decision about whether the resubmission satisfied the requirements outlined in the first rejection.

For the average drug, I'd say scheduling an added advisory panel is bad news. As in the case of Cell Therapeutics' (Nasdaq: CTIC) pixantrone, it seems to be a sign that the FDA is looking for added confirmation that the drug shouldn't be approved. If the agency was convinced the companies had their ducks in a row, the FDA could just approve the drug on its own.

But I think obesity drugs are different because they've had so many problems with side effects popping up after approval -- Wyeth's fen-phen and Abbott Labs' (NYSE: ABT) Meridia -- that the agency might be looking for confirmation to go ahead with approval. This way, if the FDA approves the drugs and side effects become a problem once they're on the market, the agency can point to the advisory panel as evidence that they weren't the only ones that weren't cautious enough.

The results of the advisory panel are always important, but it seems the stakes might be just a little higher for these. A strong recommendation for approval might be all that the FDA needs to justify an approval to those worried about perception at the agency.

Going second might give Arena a slight advantage, but the issues for the two drugs are different enough that I don't think it really helps much. Both companies need to convince the advisory panel that theoretical side effects -- fetal oral clefts for Qnexa and cancer for lorcaserin -- aren't a problem. If they can do that, it should be possible to gain FDA approval.

But that's a big if.

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