As the June 1 launch date for the Medicare discount drug card program nears, millions of elderly and disabled Americans are grappling with a bewildering array of choices.

Enrollees can select only one card and can switch cards only once. So participants are scrambling to find the one card that offers the best prices for the drugs they take. But the card sponsors and drug manufacturers have made that task nearly impossible as prices are changing even before the program has begun, say patient advocacy groups.

"I fear this is going to be extremely confusing to people," said Suzanne H. Jackson, who directs the insurance counseling center at George Washington University. "The people least able to cope with all of this complexity are being asked to fend for themselves."

Take the Pharmacy Care Alliance card accepted by CVS, Rite Aid, Giant and other large retailers. It's one of 73 being offered across the country as part of the new Medicare law. The card's enrollment booklet promises discounts of up to 20 percent on brand-name drugs and 40 percent on generics. And many of the prices for brand-name drugs are competitive.

But most are already outdated.

Since the enrollment booklet was printed in March, the Pharmacy Care Alliance has changed prices on 58 of the 93 listed brand-name drugs, a review by The Washington Post has found. Thirty prices rose and 28 declined.

And some prices can easily be beaten: Drugstore.com, for example, had better deals yesterday on 37 of the 63 drugs that were offered in 30-day quantities by both the discount card and the Internet pharmacy.

The outdated prices in the Pharmacy Care Alliance's glossy 20-page booklet underscore the challenge faced by millions of senior citizens as they search for new ways to save money -- picking a drug discount card that will be as attractive tomorrow as it is today.

Under Medicare rules, card sponsors can change their prices once a week. So a card that's best for a senior citizen one week may be the worst the next week.

Bush administration officials have trumpeted the discount card program as a way for elderly Americans to save money until the full Medicare drug benefit goes into effect in 2006. And with prices posted on the www.medicare.gov Web site and available on toll-free telephone lines, the program offers seniors new tools to compare current drug prices, they say.

"We are trying to give seniors unprecedented information on the final price of drugs," said Mark B. McClellan, who heads the federal agency that oversees Medicare.

Of course, the final price today may not be the final price tomorrow, McClellan noted in a recent interview. But Americans, he said, are accustomed to fluctuating prices.

Patient advocacy groups have predicted that the Medicare card discounts will be negated, at least to some extent, by manufacturer price hikes. And they have warned that since Medicare rules allow card sponsors to change prices once a week, some seniors will have trouble deciding which cards offer the best prices for the medications they take.

"The new drug discount card program will be very disappointing for America's seniors and will fail to make drug costs affordable," Ron Pollack, executive director of Families USA, predicted in late April, as Medicare began posting drug prices on its Web site.

The review of the Pharmacy Care Alliance program found a mix of price hikes and cuts. Some prices didn't budge at all.

Stephen E. Littlejohn, vice president of pharmacy benefit management firm Express Scripts Inc., attributed the changes to market dynamics. Express Scripts cosponsors the card with the National Association of Chain Drug Stores, an Alexandria-based trade group.

Some of these dynamics seem obvious: When drug manufacturers raise their prices, so will the discount cards. And when competing drug cards lower drugs, other cards will follow suit.

Some prices also can drop when card sponsors negotiate discounts, known as rebates, with drugmakers.

A look at the prices for Vioxx illustrates the dynamics. The Pharmacy Care Alliance's enrollment booklet offers a 30-day supply of Vioxx (25 milligrams) at $75.33. Drugstore.com was offering the arthritis drug for $77.99 yesterday.

The booklet states that its price list was last updated March 3.

On May 3, the first day Medicare beneficiaries could sign up for the discount cards, Pharmacy Care Alliance's Web site offered to fill that prescription for $85.43, 13.4 percent more than the price in the booklet.

On May 14, the drug shot up again -- this time, to $89.03, a 6 percent jump.

"There's kind of a dual dynamic that's happening here," Littlejohn said.

First, he said, drug manufacturer Merck & Co. Inc. had raised the price of Vioxx 4.8 percent after the booklet went to press in March. (A Merck spokeswoman confirmed that the price went up March 31.)

Second, rebates Pharmacy Care Alliance had been negotiating with Merck had not been finalized when the booklet went to press. Nonetheless, the booklet listed the lower, discounted prices that were anticipated for Vioxx and dozens of drugs, Littlejohn said.

Asked why the card program would publish prices that had not been finalized, Littlejohn said: "This is an important way of being transparent as we possibly can. . . . It gives people a sense of the ballpark" prices.

Littlejohn promised in an interview last week that prices would be lowered as soon as the rebates were finalized. And they were.

Yesterday, that 30-day supply of Vioxx was selling for $80.13, a 10 percent drop in a single week. Even so, the price was $4.80 higher than the one quoted in the booklet and $2.14 more than the price offered yesterday by Drugstore.com.

Medco discount drug card, above, is one of many that seniors can choose; once they elect a card, they can switch only once.