Drugs being developed for the treatment of diseases of the central nervous system (CNS) take 35% longer to complete clinical trials and receive regulatory approval than other new prescription medicines, according to a new analysis.

Between 1996 and 2010, the mean clinical-plus-approval-phase time for CNS drug treatments approved in the US was 32 months, 35% longer than the mean for non-CNS drugs approved during the same period, according to the analysis, which is published by the Tufts Center for the Study of Drug Development (CSDD).

But despite the longer and more costly development associated with CNS drugs, "the CNS new product pipeline is among the richest in the R&D-based drug industry," comments Joseph DiMasi, who conducted the study and is director of economic analysis at the Tufts Center.

The industry's CNS drug pipeline includes products to treat neurological diseases such as Alzheimer's disease, epilepsy, migraine headaches and stroke, and mental health conditions such as addictions, autism, depression, panic and schizophrenia.

The pipeline has grown by an annual average of 6% over the last decade and currently accounts for 11% of all drug development projects worldwide, the study notes. Nevertheless, development of these treatments poses a challenge for drugmakers, with the clinical approval success rate for "self-originated" CNS drugs entering clinical trials between 1993 and 2004 estimated at about one in 10. That compares to around one in six for all self-originated drugs, according to the study, which goes on to explain that "self-originated" drugs are those developed entirely by one manufacturer, in contrast to compounds which a company may obtain through licensing, purchase or other means.

Also, the "clinical approval success rate" refers to the share of New Chemical Entities (NCEs) in clinical development that eventually obtain marketing approval from the US Food and Drug Administration (FDA).

The analysis is reported in the March/April issue of the Tufts CSDD Impact Report. It also reveals that the clinical approval success rate for self-originated CNS drugs varied from a low of 7.1% for products entering clinical testing during the period from 1995 to 2000 to 14.8% - or more than double - for drugs which entered clinical testing during 1998-2003.

It also notes that the mean clinical time for CNS drugs during 1996-2010 was 102.1 months, which is 40% longer than for non-CNS drugs, while the mean approval time for these products was 20.3 months, or 13% longer than for non-CNS treatments.