US sales of "traditional" prescription drugs - for conditions such as high cholesterol and high blood pressure - declined 1.5% in 2012, the first drop on record for such treatments, say new figures.

The decline, which is reported for spending by the US commercially-insured population last year, was offset by an 18.4% increase in spending by this group on specialty medications to treat more complex diseases such as rheumatoid arthritis, cancer and hepatitis C, according to the latest annual Drug Trend Report published by pharmacy benefit manager (PBM) Express Scripts. 

Combined, total drug spending for the commercially-insured US population increased  2.7% in 2012, consistent with the rate of growth for 2011, says the firm.

The study also reports that last year, the "patent cliff" ushered in lower-cost generic alternatives for many blockbuster medications, and that utilisation increased for eight of the top 10 therapy classes, while unit costs decreased in seven.

For the second consecutive year, the US spent more on prescription drugs for the treatment of diabetes than for any other therapy class. Diabetes drug spending increased 11%, driven partly by unit cost increases for popular insulins.

Spending on drugs to treat attention disorders also rose, by 14.2%, with utilisation up 5.8% largely as a result of the increased numbers of adult patients. Unit costs were also up, rising 5.4% due to last year's shortages of active ingredients contained in many treatments in this class.

Turning to specialty medications, the report notes that these often require specialised handling or administration, frequent dosing adjustments and intensive clinical monitoring and patient assistance. While specialty conditions affect fewer than 2% of the US population, last year they accounted for 24.5% of the country's total drug spend within the pharmacy benefit - the highest percentage on record, it says.

Inflammatory conditions such as rheumatoid arthritis were the most expensive specialist category, with spending here rising 23% last year, driven by a 9% rise in utilisation and 14% higher unit costs. 

And at 33.7%, hepatitis C experienced a larger increase in drug spend for the year than any other major therapy class, either traditional or specialty. The increase is due almost entirely to two new drugs introduced in May 2011 - Merck & Co's Victrelis (boceprevir) and Vertex' Incivek (telaprevir) - says Express Scripts, which is forecasting that total spending on hepatitis C medicines will go up 32.3% this year and a further 56.3% in 2014.

Utilisation of cancer medications rose 3.4% last year and their costs grew 22.3%, with much of the latter increase being driven by new drugs developed to treat unique generic profiles, a trend that has increased in recent years, the study notes.

It also points out that the US Food and Drug Administration (FDA) approved 22 new specialty drugs last year, many of which will cost more than $10,000 per month of treatment.

And it notes that, according to the Express Scripts Prescription Price Index, prices of the most highly-utilised brand-name medications increased 12.5% in 2012, far outpacing the US Consumer Price Index's 1.7% inflation for the year, and compared to a decline in generic drug prices of 24%.