Health stocks drooped at the end of the week as safety news ripped through Biogen ( BIIB - Get Report) and Elan ( ELN), and other companies dealt with their own dose of drama.

Biogen and tumbled after the companies disclosed late Thursday two cases of a deadly brain infection in multiple sclerosis patients taking Tysabri. The companies hosted a conference call Friday morning to discuss the cases, which are the first confirmed since the drug's approval in the EU and its relaunch in the U.S.

Biogen's shares gave up $19.75, or 28%, to $50.01 and Elan fell a whopping $10.12, or 50.5%, to $9.93 as investors weighed the safety risks and reports of unconfirmed cases.

This was the second slam of the week for Elan, which fell alongside Wyeth ( WYE) after presenting data Tuesday evening on experimental Alzheimer's drug bapineuzumab at the International Conference on Alzheimer's Disease.

There's nothing to see here folks. A piece of "non-news" related to another company developing Alzheimer's treatments. Transition Therapeutics ( TTHI) issued a press release Friday to announce no material change. The biotech stock, which like Elan and Wyeth opened Wednesday lower, fell another $1.67, or 16.8% on Friday, to $8.28 on higher-than-average volume. The company reassured investors Friday that "there are no undisclosed material changes or corporate developments involving the company to account for its recent change in stock price."

Meanwhile, the Food and Drug Administration issued a "not approvable letter" denying clearance to Shering-Plough's ( SGP) sugammadex, a drug to help patients recover from anesthesia. The move came as a surprise because previously an FDA advisory panel had recommended its approval. The agency isn't required to follow the committee's recommendations (think Genentech ( DNA) and Avastin for breast cancer earlier this year), but it usually does. Schering shares were off by 67 cents, or 3.2%, at $20.41.

Elsewhere, ImClone ( IMCL) shares continued to tick higher a day after Bristol-Myers Squibb ( BMY) bid $60 a share for the 83% of ImClone's shares it doesn't already own. ImClone shares ticked up another $1.41, or 2.2%, to $65.34 Friday as investors showed anticipation for a higher bid. Bristol ended the day flat.

In earnings, Thoratec ( THOR) reported a profit of $8.7 million, or 16 cents a share, up from $1.3 million, a year prior, on revenue that climbed 44% to $82.6 million. Results smashed Street expectations for a profit of 9 cents a share on $64.2 million in revenue, according to Thomson Reuters data.

Thoratec raised its outlook, predicting an adjusted profit of 47 cents to 52 cents a share from previous guidance of 36 cents to 40 cents a share. It also increased revenue guidance, now expecting between $285 million and $295 million, up from the prior guidance for $255 million to $265 million. The stellar results boosted shares by $4.11, or 22%, to $22.87.