WASHINGTON — Growth in U.S. sales of pharmaceuticals bounced back last year as rebates and low-cost generic drugs drove an increase in the number of prescriptions filled, according to data tracking firm IMS Health.

U.S. pharmaceutical sales climbed 5.1 percent to $300.3 billion in 2009 after two prior years of slower growth. IMS Health attributed the turnaround to increased filling of prescriptions, which grew at a 2.1 percent pace compared with 1 percent in 2008.

In response to the economic downturn, drugmakers have been offering co-pay coupons and other programs to help patients pay for their prescriptions. Those programs combined with offers on low-cost generic drugs from Walmart, Walgreens and other retailers to drive sales.

“Some of those factors enabled demand to grow in what was overall a tough economic year,” said Murray Aitken, senior vice president with IMS.

Also boosting sales were price increases between 3 percent and 4 percent, roughly even with historical hikes.

While an improvement over recent years, 2009 pharmaceutical market growth remained at historically low levels due to fewer product launches and low-cost generics replacing older brand-name drugs.

Generic drugs, which often cost a fraction of branded products, made up 75 percent of all prescriptions filled last year. In 2004 generics made up just 57 percent of the market, according to IMS. The low-cost alternatives are launched after the patent on the original product expires or is successfully challenged in court.