Updated from 12:51 p.m. EDT

Earnings beats and positive news out of Amgen ( AMGN) were supporting the health care sector Thursday, even as the major markets were sliding.

Amgen said Thursday that its Aranesp anemia drug was not contributing to the deaths of patients in a Phase III lung cancer trial. The biotech giant added $2.31, or 3.6%, to $62.32.

Gilead Sciences ( GILD) reported a 55% jump in first-quarter earnings from a year ago, topping Wall Street's consensus forecast. Gilead was higher by $3.28, or 4.2%, at $81.71.

Both Amgen and Gilead are components of the Amex Biotechnology Index, but their gains merely buoyed the index's gain of 0.7%.

Among others reporting earnings, Dow Jones Industrial Average component Merck ( MRK) posted first-quarter earnings that were in line with estimates. Meanwhile, Schering-Plough ( SGP) topped estimates.

The Amex Pharmaceutical Index, of which both are components, was higher by 0.9%.

Among other winners, Monogram Biosciences ( MGRM) soared 9.5% to $2.08. Arena Pharmaceuticals ( ARNA), which posted a widening first-quarter loss that was still better than the Thomson First Call average estimate, was higher by 7.9% at $12.25. St. Jude Medical ( STJ) rose 5.5% after raising its full-year outlook.

Decliners included UnitedHealth ( UNH), which beat estimates and guided in line for the second quarter and full year. Despite the positive news, the stock lost $2.16, or 4%, to $52.05.

Wyeth ( WYE) reported a 12% rise in first-quarter earnings compared with the year-ago quarter. However, sales of the company's top-selling drug, the antidepressant Effexor, slid 6%. Wyeth lost 67 cents, or 1.2%, at $55.66.

Other health care providers lost ground as well. MedcoHealth ( MHS) was down 1.8%, Coventry Health ( CVH) slid 1.2%, and WellPoint ( WLP) was off 1.8%.

Medical-device makers were also under pressure. Stryker ( SYK) beat first-quarter earnings targets after reporting results following Wednesday's close, but the stock fell $3.09, or 4.5%, to $66.01.

Among other device makers, Zimmer Holdings ( ZMH) shed 2.1%, and Boston Scientific ( BSX) was off 0.7%.