US drugmaker Arena Pharmaceuticals has reported positive Phase II data with its obesity treatment APD356, a compound designed to affect centres in the brain regulating food intake and metabolic rate.

The 352-patient study looked at the effects of APD356 and placebo on weight loss over 28 days, and found a significant improvement for Arena’s drug, which acts on the 5-HT2C serotonin receptor. Arena said patients on a 15mg dose of APD356 lost an average of 1.3 kilograms during the period, compared to just 0.4 kilograms in the placebo group. Lower doses of APD356 did not cause statistically significant weight loss.

In addition, echocardiograms of the patients showed no apparent effect on heart valves or lung artery pressure, Arena said. This is an important finding because the combination obesity treatment regimen known as fen-phen (fenfluramine and phentermine), which was a big seller in the 1990s, had to be pulled from the market in 1997 after it was linked to heart valve damage.

The rewards for a company developing an effective drug for obesity could be substantial, as current treatments options are limited, represented by Roche’s lipase inhibitor Xenical (orlistat) and Abbott’s centrally acting Meridia/Reductil (sibutramine).

Xenical has been affected by disagreeable side effect issues that have held it back from achieving its once-promised blockbuster status, although it has still managed to garner annual revenues in the region of 600 million Swiss francs in 2003 and 2004 and could be set for a switch to over-the-counter status that will expand the franchise [[16/09/05d]]. Meanwhile, Meridia’s safety record has also been under the spotlight, despite the backing of the US Food and Drug Administration [[18/08/05a]], and sales have never really taken off. In 2002 – the last year Abbott published sales figures for the product, sales were $75 million, a decline of 11%.

So if successful, Arena’s compound could compete in an underserved market tipped to be valued at $2.5 billion dollars in 2012, five times its current value [[12/07/04h]].

Other companies vying to bring an effective obesity drug to market include Sanofi Aventis, whose Acomplia (rimonabant) drug is due for launch in the middle of next year [[23/08/05g]], and Alizyme of the UK's lipase inhibitor ATL-962, due for launch in 2008.