Merck & Co has signed a $475 million deal, including $25 million upfront, to secure rights to Neuromed Pharmaceuticals’ lead painkiller NMED-160 and related compounds.

NMED-160, in Phase II testing for arthritis pain, is a selective n-type calcium channel blocker that specifically targets the pain signals transmitted from one nerve cell to another. Preliminary clinical results suggest that the product could rival opioid analgesics in terms of their painkilling efficacy, but be free of morphine-like side effects such as addiction and motor function impairment.

If this profile is backed up in late-stage testing, Merck could have a successor to its COX-2 inhibitor Vioxx (rofecoxib) – once a $2.5 billion product but withdrawn from the market in 2004 after being linked to an increased risk of heart attacks and stroke. Pain is one of nine key therapeutic targets the US drugmaker has selected as its strategic focus, and is one of the largest pharmaceutical markets valued at around $28 billion.

Merck will finance NeuroMed’s research for two years, with the potential to renew for another two-year period, and will pay the Canadian company $202 million if NMED-160 wins approval around the world for its lead indication, rising to $450 million if it is later cleared for a second use. Neuromed will receive royalties on sales, and will retain co-promotion rights to specialist physicians in the USA.

Neuromed is also developing NMED-160 and related compounds for other indications, including epilepsy and cardiovascular diseases, which are not included in the current Merck deal.