Health stocks continued their downward course on Thursday, as big biotech and pharmaceutical companies reported better-than-expected third-quarter results.

Amgen ( AMGN) was one of the biggest winners, bounding $7.96, or 16%, to $57.66 a day after the company raised its outlook.

Shares of Celgene ( CELG) were also stronger after the company beat analysts' profit and revenue expectations for the third quarter. Additionally, Celgene's management said the company expects to exceed its prior guidance for the year. Shares were up $3.60, or 6.8%, at $56.89.

Amgen and Celgene were the only components of the Amex Biotechnology index, which was down 4.5%, that managed to stay in positive territory.

The Amex pharmaceutical index was in slightly better shape, giving up 0.1%. Pharmaceutical companies Eli Lilly ( LLY) and Bristol-Myers Squibb ( BMY) both reported their third-quarter earnings, beating expectations on an adjusted basis and boosting their estimates for the year. Bristol added 39 cents, or 2.2%, to $17.92, while Lilly shares were relatively flat by mid-afternoon.

Away from earnings, Exelixis ( EXEL) shares fell 63 cents, or 14%, to $3.87. The company announced early-stage data on one of its compounds, XL184, but also said that GlaxoSmithKline ( GSK) has effectively ended its collaboration for the cancer compound and earlier compounds in the agreement.

Glaxo will continue to develop and commercialize XL880, a compound it previously licensed. Exelixis has retained the rights to develop, commercialize and license all of the other compounds, subject to a royalty that will be paid to Glaxo.