Health site Drkoop.com has filed regulatory documents that raise "substantial doubt" about its business, news that sent its stock plummeting more than 40 percent in early trading Friday.

In an annual report with the Securities and Exchange Commission released Thursday, the company said it has "sustained losses and negative cash flows from operations since its inception," posing a threat to its future as a business. PricewaterhouseCoopers, the company's auditor, said in the filing that the company's financial data has raised "substantial doubt about its ability to continue as a going concern." In its defense, management said it intends to raise working capital through additional equity or debt financing in the upcoming year, according to the filing. The Austin, Texas-based company was not immediately available for comment. Drkoop is the latest Internet company to report that it is running low on cash. Earlier last week, online music seller CDNow said its auditor, Arthur Andersen, has also expressed "substantial doubt" about whether the company can continue to stay in business, according to an SEC filing. Thursday, online grocer Peapod said it is soliciting takeover offers from a range of suitors as the company continues to face cash flow problems.