US sales of prescription drugs grew just 1.3% in 2008, which IMS Health says is the lowest annual rate of rise since it began collecting data in 1961.

Last year the market reached a value of $291.5 billion, and US dispensed prescription volume rose only 0.9%, according to IMS. Factors influencing this slow growth included higher demand for generics, lower sales of new products and a decline in consumer demand as a result of the economic downturn. The previous lowest annual recorded rise in US prescription drug sales was in 2007, when they grew 3.8% compared with 8% in 2006, it adds.

The USA’s top-selling products by therapeutic class last year were the antipsychotics, with sales rising to $14.6 billion from $13.1 billion in 2007, and displacing the lipid regulators – the statins plus Merck/Schering-Plough’s Vytorin (ezetimibe and simvastatin) and Zetia (ezetimibe) - whose sales fell from $16.4 billion to $14.5 billion. In third place were proton pump inhibitors, dropping from $14.2 billion to $13.9 billion year-on-year, followed by seizure disorder treatments, rising from $10.2 billion to $11.3 billion. In fifth place were the antidepressants, advancing slightly from $9.4 billion to $9.6 billion.

The top-selling prescription drug in the USA last year continued to be Pfizer’s cholesterol-lowerer Lipitor (atorvastatin), although its turnover fell to $7.8 billion from $8.1 billion in 2007. In second place was AstraZeneca’s acid reflux treatment Nexium (esomeprazole), up from $5.5 billion to $5.9 billion, then Sanofi-aventis/Bristol-Myers Squibb’s clot-buster Plavix (clopidogrel), rising from $3.9 billion to $4.9 billion, followed by GlaxoSmithKline’s asthma treatment Advair Diskus (fluticasone propionate), up slightly to $4.4 billion from $4.3 billion. Fifth was AstraZeneca’s Seroquel (quetiapine fumarate) for bipolar disorder, up to $3.9 billion from $3.5 billion.

The first branded drug to feature on the list of leading drugs in terms of US dispensed prescriptions was Lipitor, sliding from $65.1 billion to $57.9 billion and in fifth place behind HYCD/APAP, lisinopril, simvastatin and levothyroxine sod.

Biotechnology medicines accounted for 15% of last year’s market, with sales totalling $45.9 billion, IMS also reports.