Updated from 2:30 p.m. EDT

Shares of aaiPharma ( AAII) were among the worst-performing health and pharmaceutical stocks Friday, falling 18.1% after the company said it would not be able to make its $10 million interest payment scheduled for today.

Lenders have granted the drugmaker a 30-day grace period, but if the company fails to make the payment by Oct. 31 it will be in default. The company said there is a likelihood that it will be in default of certain covenants under its senior credit facility; the company is seeking waivers and consents for these defaults. Shares traded down 28 cents to $1.27.

Cyberonics ( CYBX) fell 7.9% after Advanced Neuromodulation Systems ( ANSI) dropped its $22-a-share offer for the company. "We are disappointed that the Cyberonics board of directors has chosen to reject our invitation to discuss a business combination," ANSI said. ANSI, which owns about 14.7% of Cyberonics, will continue to manage its investment as a shareholder, saying "we genuinely wish Cyberonics the best as it works toward fulfilling its mission." Shares of Cyberonics traded down $1.61 to $18.85. Shares of ANSI traded up 52 cents to $30.87.

Shares of Nastech Pharmaceutical ( NSTK) fell 8.3% after the company filed an $80 million shelf registration statement with the Securities and Exchange Commission. The pharmaceutical company said that proceeds from any future products would be used for general corporate purposes. Shares traded down $1.18 to $13.11.

eResearchTechnology ( ERES) fell 2.8% after it lowered its third-quarter financial outlook and warned that results would miss expectations. The company now expects earnings of 13 cents to 14 cents a share on sales of $27 million to $28 million. Previously, it forecast earnings of 16 cents to 17 cents a share on sales of $30 million to $30.5 million. Analysts polled by Thomson First Call had expected earnings of 16 cents a share on sales of $30.7 million. Third-quarter results were hurt by delays in phase I studies, the company said.

Looking ahead, eResearch now expects full-year earnings 58 cents to 60 cents a share on sales of $112 million to $115 million. Previously, it forecast earnings of 62 cents to 63 cents a share on sales of $117 million to $119 million. Analysts had expected earnings of 61 cents a share on sales of $118.8 million. Shares traded down 37 cents to $12.96.

Even as the company cut third- and fourth-quarter sales guidance, shares of Conceptus ( CPTS) rose 1.6% Friday. The company now expects third-quarter sales of $2.8 million, down from its previous guidance of $3.2 million to $3.4 million. For the fourth quarter it now expects sales of $3.4 million to $3.6 million, down from its previous guidance of $3.6 million to over $6 million. Analysts had been expecting third-quarter sales of $3.4 million and fourth-quarter sales of $5.4 million. Shares traded up 15 cents to $9.42.

Other health care volume movers included Merck ( MRK), up 31 cents to $33.31; Pfizer ( PFE), up 37 cents to $30.97; Amgen ( AMGN), up 95 cents to $57.76; Schering-Plough ( SGP), down 11 cents to $18.95; and Johnson & Johnson ( JNJ), up 67 cents to $57.

If you liked this article you might like

Thursday's Tech Winners & Losers

Thursday's Tech Winners & Losers

Thursday's Winners & Losers: FTD

Thursday's Winners & Losers: FTD

Wednesday's Winners & Losers: Superior Offshore

Wednesday's Winners & Losers: Superior Offshore

Wednesday's Tech Winners & Losers

Wednesday's Tech Winners & Losers

Tuesday's Winners & Losers: Fossil

Tuesday's Winners & Losers: Fossil