The U.S. government finalized rules on Wednesday meant to make it easier for seriously ill patients to gain access to unapproved medicines when they have run out of other options.

The regulations spell out more clearly which patients are eligible for special access to experimental medicines, the Food and Drug Administration said. They also clarify when manufacturers can charge patients for the drugs.

The move aims to achieve a balance between the need to gather information to demonstrate whether drugs work and the fact that critically ill patients urgently want access, FDA Commissioner Margaret Hamburg told reporters.

Under the rules, companies may obtain FDA permission to charge patients in order to recover their costs under certain circumstances. The goal is to encourage more companies to provide the medicines to appropriate patients, said Dr. Janet Woodcock, head of the FDA's Center for Drug Evaluation and Research.

Patients can try experimental drugs through clinical trials, but enrollment in the studies is limited, creating a push for other options.

Experimental medicines have been available to patients outside clinical trials under certain circumstances since the 1970s. Tens of thousands of patients with AIDS, cancer and other conditions have used medicines through those programs, the FDA said.

Patient groups have long been pushing for the FDA to expand access for desperate patients.

The Abigail Alliance for Better Access to Developmental Drugs, an advocacy group, said the FDA needed to go further to significantly boost access.

The new rules are just codifying the status quo, said Steve Walker, the alliance's co-founder. Companies often see providing a drug to a patient outside of clinical trials as an economic burden and a regulatory risk. We don't expect there to be much of a change in availability.

In 2008, the Supreme Court rejected an appeal by the Abigail Alliance and another group arguing that dying patients have a constitutional right to access experimental drugs that are not FDA approved.

Lynda Dee, a founding member of the AIDS Treatment Activist Coalition, said the FDA's effort would be helpful to doctors and patients alike by giving a clear picture of their options. Speaking on an FDA conference call with reporters, Dee said she was working with a group of AIDS patients developing a bid to try an experimental drug.

FDA spokeswoman Karen Riley said the agency estimated the new rules would prompt a 50 percent increase in individual patient applications for experimental drugs, which now average 659 a year.

Applications for between 10 and 100 patients are expected to jump 25 percent to 50 percent. About 55 applications of that size were received between 2000 and 2002, Riley added.

Details were posted on the FDA website here