Bristol-Myers Squibb Co.'s (BMY) second-quarter profit declined 28%, as sales were eroded by recent patent expirations for top-selling drugs including the anticlotting pill Plavix.

The New York drug maker also lowered its forecast of full-year 2012 earnings.

Bristol-Myers plans to get through the patent losses for Plavix and other drugs by boosting sales of newer drugs. The company hopes to bolster its product lineup with its recent agreement to purchase diabetes-drug maker Amylin Pharmaceuticals Inc. (AMLN) for $5.3 billion.

In May, Bristol-Myers lost U.S. patent protection for Plavix, which is used to stave off recurrent heart attacks and strokes. This exposed the brand to lower-priced competition from generic versions, and Bristol's second-quarter Plavix sales tumbled 60% to $741 million. Bristol-Myers co-markets the drug with Sanofi (SNY).

Another blow was the March loss of patent protection for blood-pressure medications Avapro and Avalide, which pushed combined sales of those drugs down 53% to $117 million.

Bristol and other drug makers are in the midst of a wave of patent expirations for blockbuster drugs that have pressured sales. Bristol has had some success bringing new drugs to market to help offset the patent losses, but it also has experienced some research setbacks.

For the second quarter, Bristol's profit fell to $645 million, or 38 cents a share, from $902 million, or 52 cents a share, a year earlier. Excluding certain costs such as asset impairments, earnings were 48 cents a share, matching the mean estimate of analysts surveyed by Thomson Reuters.

Overall sales declined 18% to $4.44 billion, just ahead of the Thomson mean estimate.

U.S. sales dropped 27% to $2.6 billion, while non-U.S. sales fell 1% to $1.9 billion.

Although sales for Plavix and the blood-pressure medications declined substantially, sales for other top products increased, ranging from a 1% gain for antipsychotic Abilify to a 71% jump for skin-cancer treatment Yervoy.

Bristol-Myers continues to try to bring more drugs to market. One of the most closely watched is Eliquis, an anticlotting drug co-developed with Pfizer Inc. (PFE). The U.S. Food and Drug Administration declined to approve it in June, asking for more information about clinical data. Analysts believe the drug could be a multibillion-dollar seller.

Bristol also is developing new drugs for cancer and hepatitis C that have shown promise in studies.

The company, however, recently disclosed negative clinical results for experimental liver-cancer drug brivanib. And the FDA has declined to approve the diabetes drug dapagliflozin, developed in partnership with AstraZeneca PLC (AZN).

Bristol said Wednesday an advisory committee of the European Union issued a positive opinion on the company's proposed subcutaneous formulation of anti-inflammatory drug Orencia. A European Commission decision is pending.

The company lowered its forecast of 2012 earnings to a range of $1.78 to $1.88 a share from a prior range of $1.90 to $2 a share. However, Bristol didn't change its forecast of adjusted earnings, which exclude certain items, of $1.90 to $2 a share. Bristol said the unchanged adjusted earnings forecast factors in the expected three-cents-a-share negative impact related to the planned Amylin acquisition.

Write to Peter Loftus at peter.loftus@dowjones.com

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