US spending on specialty prescription drugs - those used to treat chronic, complex diseases such as cancer, multiple sclerosis (MS) and rheumatoid arthritis (RA) - is projected to increase 67% by the end of 2015, say new forecasts.

US prescription drug spending on eight of the top 10 specialty therapy classes will continue to increase over the next three years, due to the robust pipeline of new biologicals and also to physicians delaying treatment of patients until the new drugs are on the market, according to the study, from pharmacy benefit manager (PBM) Express Scripts. 

"New specialty treatments are making a real difference in the lives of patients, but the very high cost of these drugs creates difficult decisions for plan sponsors on which medicines to cover," commented Dr Glen Stettin, senior vice president for clinical, research and new solutions at Express Scripts. Specialty medicines require special handling, distribution and administration and are frequently delivered through an injection or infusion, the company notes. 

By the end of 2015, cancer, MS and RA will each commend higher drug spending than any other therapy class in the US except diabetes, the company forecasts.

It also expects spending on hepatitis C treatments to quadruple over the next three years - the largest percentage increase by far among therapy classes. By the end of 2015, spending on hepatitis C medications will exceed that of much more common conditions, such as high blood pressure, as a result of the new interferon-free medications which are expected to gain approval from the Food and Drug Administration (FDA) next year, as well as greater numbers of diagnoses resulting from new screening guidelines.

One significant support for dealing with the rising cost of specialty medications would be an improved pathway for biosimilars; Express Scripts has forecast that the US would save $250 billion between 2014 and 2024 if the 11 most likely biosimilar candidates were to be launched in the country.

The report forecasts that overall spending in the US on traditional prescription drugs - mostly pills used to treat common conditions such as high cholesterol and depression - will decline 4% by the end of 2015, largely because of the availability of generic medicines. Only two of the top 10 traditional therapy classes - diabetes and attention disorders - are likely to have spending increases over next three years, but those increases will be significant, it warns.

In 2011, diabetes became the costliest prescription drug therapy class in the US and, according to the new projections, it will continue to hold that distinction at least to 2015. Over the next three years, speeding on diabetes medications will rise an additional 24% because of high prevalence and a robust pipeline of new therapies, Express Scripts forecasts.

Turning to attention disorder therapies, the report projects that, despite the availability of generic drug versions of many such treatments, spending in the category will increase approximately 25% over the next three years, driven by increased utilisation among middle-aged adults and wide geographic variation in diagnosis. 

For example, while the prevalence, medical use and associated medical and pharmacy costs for attention disorders is highest in the southern part of the US, the northeastern region of the country experienced rapid growth in attention disorder diagnosis from 2008 to 2010, and its associated costs grew nearly 60%.