NORWALK, Conn. - Sales growth in the U.S. prescription drug market slowed to the lowest rate in 46 years in 2007 as more brand-name drugs lost their exclusivity to generics and new product approvals declined, according to a report issued Wednesday.

Sales came to US$286.5 billion in 2007, up 3.8 per cent, IMS Health said in its annual U.S. Pharmaceutical Market Performance Review. The rate of growth was the lowest since 1961, when sales increased by 3.3 per cent.

In contrast, prescription drug sales grew by eight per cent in 2006.

Growth moderated beginning in 2001, but picked up in 2006 with the start of the federally subsidized prescription drug program for seniors, Norwalk-based IMS Health said. However, growth slowed again last year.

The Medicare Part D program accounted for 19 per cent of retail prescriptions at the end of last year, a modest increase over 2006 "and reflective of a maturing program," IMS said in its report. It said 65 per cent of Americans 65 and older are now enrolled in the program.

Volume for generic drugs grew by 10 per cent as branded pharmaceuticals with $17 billion in sales lost exclusivity. Generics increased their share of total dispensed prescriptions to more than 67 per cent.

IMS Health reported that antidepressants, lipid regulators, codeine and combination pain medications, blood pressure drugs and beta blockers continued to top the market in prescription use.

Sales growth in 2007 was affected by a significant number of warnings, product withdrawals and safety concerns raised by the U.S. Food and Drug Administration for various products, the report said.

Diana Conmy, corporate director of market insights at IMS Health, said safety issues were among "some of the things we could not have anticipated."

IMS estimated that 68 major warnings were issued in 2007, up from 58 in 2006 and 21 in 2003.

Safety issues contributed to "significantly lower-than-expected sales" for products that accounted for about 10 per cent of total prescription market, the report said.

IMS Health also said drug sales are expected to rise by between three per cent and six per cent through 2012 due to aging baby boomers, increased access to drugs through the Medicare Part D program and the rising use of biotech and other products.

However, the report said patients are increasingly sensitive to higher drug prices, expiration of patents are at an all-time high with therapeutic substitution an increasingly used alternative, and legislative and policy action are a "wild card."