"Unnecessary" use of higher-priced medicines accounted for nearly all of the $2.1 billion in wasted pharmacy-related spending last year for US workers' compensation payers, claims a new report.

The money was wasted because therapeutically-equivalent, lower-cost generic alternatives were available, says pharmacy benefits manager (PBM) Express Scripts, in a new report on workers’ compensation drug benefits, for which around 125 million employees in the US are eligible.

A further $107 million was wasted last year through use of out-of-network pharmacies and third-party billing for such benefits, plus $40 million from the use of more expensive delivery channels such as retail pharmacies instead of home delivery for long-term medications used by injured employees.

Nevertheless, Express Scripts' workers' compensation clients saw overall pharmacy-related spending fall 1.8% last year, which is the second consecutive annual decline and was despite 2011’s costs per prescription rising 1.5%. Utilisation was down 3.7%, due to greater use of generics.

The highest annual cost per user in 2011 for the PBM's workers' compensation clients was reported for narcoleptic analgesics, at $508, and which accounted for about 38% of total drug spending and 34% of total utilisation, the report notes. Costs per user for compounded prescriptions - those which are not available commercially in the strength, dosage, form or exact combination needed by the patient - increased 13.7%.

The top six therapy classes - which include anticonvulsants, anti-inflammatory and dermatological medications, in addition to narcotic analgesics - represented 76.2% of total drug spending by workers’ compensation payers last year, the study also reports. Purdue Pharma/Mundipharma/Napp Pharmaceuticals' painkiller OxyContin (oxycodone) had the highest per-user cost and accounted for 10% of total drug spending last year, while the highest cost increase of any therapy class was seen for dermatological treatments, up 7.4%.

- Express Scripts has also reported this week that US spending on prescription drugs in total rose just 2.7% last year, which is the lowest annual rise ever recorded by the PBM in its 18 years of measuring the statistic. Spending growth for traditional medicines was just 0.1%, while for specialty drugs the increase was 17.1%, led by hepatitis C, where the introduction of two new medications during the year contributed to a near-doubling of drug spending to treat the disease.

The top three specialty classes - inflammatory conditions, multiple sclerosis and cancer - represented 57.6% of total spending on specialty drugs. Expenditures on drugs to treat diabetes rose 7%, and these treatments now account for the nation's largest drugs spend, the firm adds.