Abbott Laboratories (ABT) posted a 53% jump in first-quarter profit, boosted by a gain related to a terminated joint venture that helped offset disappointing sales.

But shares of the Abbott Park, Ill., medical-products company dropped to their lowest level since 2006 after revenue fell short of Wall Street expectations, with a marked slowdown in sales growth for the blockbuster anti-inflammatory drug Humira that had been a driver of Abbott's success in recent years. Unfavorable currency-exchange rates and inventory reductions hurt sales.

Abbott scaled back its forecast for full-year 2009 Humira sales growth, now calling for growth of 15% to 20% from a previous projection of more than 25%. Humira sales grew 47.6% last year to $4.5 billion. The reduced view seemed to confirm some investors' fears that prescription growth was slowing down - fears that have contributed to a 20% year-to-date decline in Abbott's previously high-flying stock price.

The weak economy hurt Abbott's results. An increasing percentage of U.S. patients aren't refilling prescriptions, Abbott Chief Executive Miles White told analysts. He also cited rising copays and other changes in drug-benefit plans that are hurting drug sales.

Until recently, Abbott shares had been outperforming most other drug makers because its diversified business model provided some protection from forces that were hurting companies more heavily concentrated in pharmaceuticals. But recently some analysts have begun to question Abbott's prospects, citing concerns about future growth of Humira and Abbott's cholesterol-related drugs.

Credit Suisse analyst Catherine Arnold said the reduced forecast for Humira "suggests the product's growth may be starting to slow." Humira competes with Enbrel from Amgen Inc. (AMGN) and Wyeth (WYE), and Remicade from Johnson & Johnson (JNJ) and Schering-Plough Corp. (SGP).

White, expressing annoyance at the market reaction to the news, said Humira still had strong prospects and would add several billion dollars in sales in coming years.

Abbott shares fell $2.10, or 4.7%, to $42.63 recently.

Abbott said net income for the three months ended March 31 rose to $1.44 billion, or 92 cents a share, from $938 million, or 60 cents a share, a year earlier. The latest quarter included a gain of $505 million, or 32 cents a share, for the "derecognition" of a contingent liability that was recorded in connection with last year's conclusion of a joint venture with Takeda Pharmaceutical Co. (4502.TO), plus other one-time items. Excluding these, earnings were 73 cents a share, or 3 cents ahead of the mean estimate of analysts surveyed by Thomson Reuters.

First-quarter sales were off 0.7% at $6.72 billion, below analyst expectations of $7.06 billion, according to a survey by Thomson Reuters.

Abbott's feat of exceeding earnings expectations despite missing revenue expectations was similar to what its larger rival, J&J, reported Tuesday in its first-quarter results. Many drug and medical-product companies have been cutting costs to bolster the bottom line amid pressure on the top line, although Abbott's total first-quarter operating costs and expenses did increase slightly from a year earlier.

Abbott's biggest unit, pharmaceuticals, posted a sales decline of 5.7% to $3.64 billion, with negative currency rates more than offsetting a slight operational sales gain.

Sales of Humira, which treats rheumatoid arthritis and other conditions, rose 16.7% to $1 billion. Abbott said unfavorable currency rates reduced non-U.S. sales growth by about 20 percentage points, worse than expected. Sales of anti-HIV drug Kaletra dropped 17% to $292 million, while sales of anti-seizure drug Depakote plunged 64.5% following its exposure to generic competition last year.

Abbott's nutritional sales, which include Similac baby formula, rose 6.4% to $1.18 billion. Diagnostics sales declined 1.8% to $816 million.

Abbott's vascular sales jumped 43% to $645 million, helped by Abbott's coronary stent devices, including the new Xience drug-coated stents. Coronary stent sales more than doubled to $402 million.

Despite its recent challenges, Abbott reiterated its forecast of full-year 2009 earnings of $3.65 to $3.70 a share. For the second quarter, Abbott expects earnings of 87 cents to 89 cents a share, excluding certain items.

Analysts expect earnings of 88 cents a share for the second quarter and $3.67 a share for full-year 2009.

White played down the notion that Abbott would have to significantly change its strategy in coming years. He also insisted Abbott didn't "compete" to acquire Wyeth, which agreed in January to be bought by Pfizer Inc. (PFE) in a deal originally valued at $68 billion.

Abbott was reportedly the "Company X" cited in Pfizer and Wyeth regulatory filings as having had preliminary talks with Wyeth in December for a potential takeover, before deciding not to pursue it. White said Wednesday Abbott isn't evaluating any large acquisitions, and didn't need such large deals to achieve its financial and strategic objectives.

-By Peter Loftus, Dow Jones Newswires; 215-656-8289; peter.loftus@dowjones.com

(Mike Barris and Jon Kamp contributed to this report.)