It's difficult for physicians treating the 23 million Medicare members who have drug benefits to learn which treatments are approved by 1,875 insurers, said authors of the study in tomorrow's Journal of the American Medical Association. Some states have more than 100 plans, confusing doctors and imperiling patients, said lead researcher Chien-Wen Tseng of the University of Hawaii.

Patients have to pay higher co-payments for drugs that aren't on a plan's approved list under the Medicare drug benefit that took effect last year. If it were easier for doctors to learn which drugs are widely accepted before writing prescriptions, patients would save money and be more likely to follow medical orders, Tseng said.

"It can be inconvenient for doctors, but the worst thing is when the patient has problems with their health because of a delay," said Tseng in a telephone interview today from Honolulu. "It costs a lot of money to provide this benefit, and we should just make it as workable as possible."

Medicare will spend $768 billion on drug coverage during the next 10 years, U.S. health officials said. Patients who enroll in the plans pay monthly premiums.

The three biggest providers of Medicare prescription benefits are UnitedHealth Group Inc., of Minnetonka, Minnesota, WellPoint Inc., of Indianapolis, and Humana Inc. of Louisville, Kentucky.

The study reviewed 75 drugs, looking at lists of approved medicines from 72 Medicare plans in California and 43 in Hawaii.

Of the drugs studied, 45 percent were described as widely covered, meaning they were on at least 90 percent of the plans' lists and had monthly patient co-payments of $35 or less with no requirement of prior authorization by the insurer.

The plans tended to favor less costly generic drugs, Tseng said. About 27 percent of generics weren't widely covered, compared with 94 percent of name-brand medicines, she said.

It's impractical for busy physicians to research the list of approved drugs for each patient's plan, said Tseng. The data should be made easily available through a personal digital assistant, electronic prescribing software or an interactive Web site, Tseng said.

The U.S. Centers for Medicare and Medicaid Services already has a Web site that identifies which drugs are approved by different prescription drug plans by state.

"Ideally they would look up every drug for every patient who walks in," Tseng said of physicians. "In a really busy practice, that's impractical and time-consuming."

Doctors also need to consider the co-payment levels of different drugs through different insurers, said Tricia Neuman, director of Medicare policy at the Kaiser Family Foundation.