U.S. prices for brand-name drugs on average rose at 2.5 times the rate of inflation last year, while generic drug prices remained flat, according to a study released on Tuesday by the nation’s largest lobby for the elderly.

Manufacturer prices for branded medicines rose 7.1 percent in 2004 compared to 7.0 percent in 2003, an AARP report found. During the same period, the general inflation rate climbed to from 2.3 percent to 2.7 percent, it said.

2004 was the fifth straight year the rise in drug prices outpaced inflation, AARP said.

“Drug prices are continuing to go up,” said David Gross of AARP’s Public Policy Institute, which conducted the review along with the University of Minnesota’s Prime Institute.

Researchers surveyed prices for 195 prescription medicines used most by Americans aged 50 and older. Of those drugs, 185 had price increases higher than inflation while nine saw price increases less than inflation.

The price for one drug, AstraZeneca LP’s Prilosec, remained flat last year. Prilosec switched from prescription to over-the-counter sales in late 2003.

Medicines with the largest price hikes since 2003 were Wyeth’s Premarin, Novartis AG’s Miacalcin, Pfizer Inc.‘s Neurontin, Sanofi-Aventis’s Amaryl and Lantus, and Boehringer Ingelheim Pharmaceuticals Inc.‘s Combivent and Atrovent.

Most older patients take about three different medications, according to the report, and the increase meant they would have to pay an average of $154.68 more last year for their drugs.

For generic drugs, however, “there was almost no price increase” on average, Gross said.

Prices for 75 unbranded medicines used most often by older Americans rose 0.5 percent last year, compared to a 13.3 percent price increase in 2003.

AARP, formerly known as the American Association of Retired Persons, conducted the study as part of its ongoing quarterly review of drug prices.