US prescription drug sales rose 5.1% to $300 billion in 2009, according to IMS Health, buoyed in part by increased use of specialty treatments, a relatively easy year in patent expiries and the absence of major safety problems. But don’t break out the party favors just yet, branded drug makers – generics continue to gain share and now account for 75% of dispensed prescriptions.

That’s a big improvement over 2008’s 1.8% growth, but it’s still pretty meager compared to the double-digit gains common until 2007.

“In 2009, demand for pharmaceuticals proved stronger than in the prior two years, yet remained at historically low levels,” said IMS’s Murray Aitken, SVP healthcare insight, in a statement. “While the 32 innovative products launched last year brought important new treatment options to patients in a number of disease areas, including cancer, thrombosis and atrial fibrillation, they drove only a limited increase in drug spending. Access for the first time to lower-cost generic treatment options in the areas of epilepsy, migraine and immune system disorders had a more moderate impact on market growth than generic launches in previous years. Stronger patient demand for prescription drugs throughout 2009, both for new therapy starts and refills, underscores the resilience of pharmacotherapies in today’s healthcare equation.”

Dispensed prescriptions in retail channels grew 2.1% to 3.9 billion prescriptions – compared to 1% growth in 2008. The volume of new therapy starts in the 17 major chronic disease areas actually dipped by 1%, but add-on therapy starts, switches and refills rose 2%, IMS said.

Another factor in the bump, said IMS, was “sustained pricing practices by pharmaceutical manufacturers competing on the basis of clinical evidence and value.”

Generics, including branded generics, now comprise three-quarters of all dispensed prescriptions in the US, having risen 5.9% in 2009, while the number of branded prescriptions declined 7.6%. In 2004, generic drugs comprised just 54% of dispensed prescriptions in the US.