As the Senate Finance Committee launched an investigation Tuesday into the relationship between makers of narcotic painkillers and the groups that champion them, a leading advocacy organization said it was dissolving “due to irreparable economic circumstances.”

The American Pain Foundation, which described itself as the nation’s largest organization focused on patients’ pain, was the subject of a December investigation by ProPublica in The Washington Post that detailed its close ties to drugmakers.

The group received 90 percent of its $5 million in funding in 2010 from the drug and medical-device industry, ProPublica found, and its guides for patients, journalists and policymakers had played down the risks associated with opioid painkillers while exaggerating the benefits from the drugs.

It is unclear whether the group’s announcement Tuesday evening — that it would “cease to exist, effective immediately” — was related to letters senators Max Baucus (D-Mont.), the finance panel chairman, and Charles Grassley (R-Iowa) sent earlier in the day to the foundation, drug companies and others.

In the letters, the senators cited an “an epidemic of accidental deaths and addiction resulting from the increased sale and use of powerful narcotic painkillers.” That class of drugs includes popular brand names like Oxycontin, Vicodin and Opana.

Growing evidence, they wrote, suggests that drug companies “may be responsible, at least in part, for this epidemic by promoting misleading information about the drugs’ safety and effectiveness.”

The American Pain Foundation’s Web site carried a statement Tuesday night saying its board voted May 3 to dissolve the group because it couldn’t stay “operational.” The foundation did not respond to requests for comment Tuesday.

The senators are targeting a who’s who of the pain industry, seeking extensive records and correspondence documenting the links, financial and otherwise, between them and the makers of the top-prescribed painkillers.

The senators’ letters also cite reporting by the Milwaukee Journal Sentinel and MedPage Today that found the companies’ close ties extended to physician societies and academic research groups.

The letters went to three pharmaceutical companies — Purdue Pharma, Endo Pharmaceuticals and Johnson & Johnson — as well as to five groups that support pain patients, doctors or research: the American Pain Foundation, the American Academy of Pain Medicine, the American Pain Society, the Wisconsin Pain and Policy Studies Group, and the Center for Practical Bioethics.

The Federation of State Medical Boards, the trade group for agencies that license doctors, received a letter, as did the Joint Commission, an independent nonprofit group that accredits hospitals nationwide and made pain management a national priority in 2001.

The senators requested information on payments since 1997 to 10 groups and eight people, including two doctors featured in ProPublica’s December report. They asked about any influence the companies had on a 2004 guide for doctors about pain that was distributed by the Federation of State Medical Boards, on guidelines by the American Pain Society and on the American Pain Foundation’s Military/Veterans Pain Initiative.

Patients in serious pain need access to opioids, the senators wrote, but drugmakers and health-care groups “must distribute accurate information about these drugs in order to prevent improper use and diversion to drug abusers.”

Concerns about the overuse and abuse of painkillers have intensified in recent years. As sales of the powerful drugs have boomed — rising 300 percent since 1999 — so, too, have overdose deaths. Opioids were involved in 14,800 overdose deaths in 2008, more than cocaine and heroin combined, according to the U.S. Centers for Disease Control and Prevention.

Pain doctors and patient groups say that while overdoses are a legitimate concern, only a small percentage of deaths involves patients who get them from their doctors. Most involve illicitly obtained drugs, statistics show.

The groups also say that patients have a low risk if they do not have addictive personalities and that any restrictions should not punish patients who suffer from serious pain.

Ornstein and Weber report for ProPublica, a nonprofit investigative newsroom in New York. A longer version of this article is available at