Drug developer

ViroPharma

(VPHM)

rose on an upgrade by Piper Jaffray analyst Thomas Wei to an outperform rating. "We believe that the recent stock decline creates a favorable risk/reward profile for the stock," the analyst wrote in a research note. Wei reiterated his $12 price target on the shares. ViroPharma was up 9.4% to $8.51.

Medical-device maker

Cyberonics

(CYBX)

saw its shares plunge 29% to $15.26 after the company offered weak first-quarter estimates and lowered its full-year guidance.

First-quarter sales are expected to be about $33.5 million, compared with $27 million in the year-ago quarter, but analysts were calling for $38 million. The company also said it doesn't expect to reach profitability until coverage for its device for treatment-resistant depression improves and investigations into its stock-option grants end.

Legal and accounting fees related to the probes will likely exceed $3 million. Additionally, Cyberonics received a Nasdaq Letter on July 31 indicating that it was failing to comply with the filing requirement for continued listing and that its securities are subject to delisting. The company will request a hearing before a Nasdaq Listing Qualifications Panel.

Health care benefits provider

Centene

(CNC) - Get Report

fell following a downgrade from Goldman Sachs. Analyst Matthew Borsch said he sees "a less favorable risk/reward combination relative to our other buy-rated names." He cut the stock to neutral from his previous buy rating and lowered his price target by $2 to $18. Shares were 1.9% lower, at $15.94.

Bio-Reference Laboratories

(BRLI)

was hit with a downgrade from Jefferies & Co. analyst Arthur Henderson, who lowered his rating on the stock to hold from buy.

Given the company's size and the level of competition in the lab service space, "BRLI's valuation seemed full to us, and we think a hold rating is more appropriate at this time," Henderson wrote in a report. From a business perspective, however, he remains bullish on the company. Shares fell 10.7% to $21.03.

Biogen Idec

(BIIB) - Get Report

shares fell despite an announcement from it's multiple sclerosis drug partner

Elan

(ELN)

that sales of MS drug Tysabri will be a significant contributor to its future profitability. Tysabri was pulled from the market last year after being linked to a potentially fatal brain disease, but it was reapproved for certain uses in June.

Biogen Idec shares fell 1.7% to $41.32. Elan lost 2.9% to $14.90 following the company's

earnings report Tuesday.