Even the most price-conscious value investors have to marvel when a company or product posts double-digit growth from one quarter to the next. Alexion Pharmaceuticals' (Nasdaq: ALXN) only marketed drug, Soliris, sure seems to be fitting that bill.

Soliris was approved last year in the U.S. to treat a rare blood disorder that affects less than 10,000 people in North America and Europe. It's now in testing to treat much more prevalent indications as well. With less than five full quarters on the market, Soliris' sales growth can only be compared sequentially; on this basis, sales rose 34% from Q4 2007 to Q1 2008. Thanks to the strong sales uptake, Alexion boosted full-year 2008 guidance for Soliris sales by $10 million to $15 million, for a total between $215 million and $225 million.

Alexion also reported a positive non-GAAP earnings surprise of $0.04 a share, though it hasn't yet released its cash flow statement for the quarter. Non-GAAP profits are pretty meaningless if they aren't eventually accompanied by positive cash flow, so Alexion gets no points from me here yet.

New-to-market drugs like Soliris are always exciting to follow, because analysts' (and drugmakers') estimates for their early sales growth tend to be less than accurate. This uncertainty can leave drug stocks significantly mispriced, for better or worse. Witness Alpharma (NYSE: ALO), the most interesting such case in the past couple of weeks, with Progenics Pharmaceuticals (Nasdaq: PGNX) likely next on the list. As for Soliris, its initial sales seem better than expected, but let's see what the future holds.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has an A+ disclosure policy.