The release of briefing documents ahead of a Food and Drug Administration advisory committee meeting always adds a bit of uncertainty to a stock. It seems Optimer Pharmaceuticals' (Nasdaq: OPTR) investors had little to worry about for tomorrow's meeting of the Anti-Infective Drugs Advisory Committee. After the documents for committee members were released Friday, shares shot up 11%.

That seems about right. The FDA concluded that Optimer's fidaxomicin is as effective as ViroPharma's (Nasdaq: VPHM) Vancocin in curing infections, and is superior to Vancocin at preventing recurrences.

An approval of fidaxomicin will almost certainly have an effect on Vancocin's sales, but it'll have a marginal effect of ViroPharma's valuation. Investors have priced in expected generic competition, and ViroPharma has become less reliant on Vancocin since the launch of Cinryze.

If generic versions of Vancocin eventually make it to market, I don't think it'll affect sales of fidaxomicin much. The antibiotic doesn't have to be taken for that long, so the difference in the price of copays isn't as big of a deal as it is for something like cholesterol drugs, which have to be taken long term. Generic versions of Merck's (NYSE: MRK) Zocor indirectly affect Pfizer's (NYSE: PFE) Lipitor and AstraZeneca's (NYSE: AZN) Crestor because patients prefer the lower copay for generics available under many insurance plans.

There's a human element to advisory committee meetings, which means Optimer isn't completely out of the woods yet. One expert on the panel might have an axe to grind, or just latch onto one piece of safety data without looking at the larger picture. But the general upbeat tone of the briefing documents should give investors confidence that a unanimously positive recommendation isn't required for the FDA to sign off on the drug. I'd guess a 5-2 vote recommending approval should be enough to gain approval from the agency next month.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.