Shares in UK drug group Shire closed down a little over 1% last night after promising results from a head-to-head study of its phosphate binder Fosrenol and Genzyme’s Renagel failed to alight investor enthusiasm.

The trial, findings of which were published in the journal Clinical Nephrology, pitted Fosrenol (lanthanum carbonate) against Renagel (sevelamer) in patients with chronic kidney disease (CKD) on haemodialysis over a four week period, assessing their ability to reduce levels of phosphate in the body.

Looking at the intent to treat population and using an analysis method based on last observation carried forward - which means that if patients left the trial early their last recorded serum phosphorus measurement was used as the end of treatment value – a greater reduction was seen in the Fosrenol group though the difference failed to reach statistical significance.

However, an analysis of the completer population - which took into account only the serum values of patients completing the four-week study - did reveal a statistically significant greater reduction in serum levels in trial arm given Shire’s drug.

The study investigators suggest that this is the more relevant analysis and that the results indicate Fosrenol may be the more effective phosphate binder, but caution that more research is required to assess whether the trends seen in the cross-over study are replicated in the long term.

Fosrenol was first approved in 2004 for the reduction of phosphate levels in patients with endstage renal disease, in which hyperphosphataemia is most common. The management of hyperphosphataemia – which occurs as the kidneys lose their ability to excrete phosphate – is crucial for patients, as excess levels can lead to serious health problems such as cardiovascular disease and brittle bones and an increased risk of death.

News of the drug’s potential superiority over its rival could give its sales a further boost, though it seems they are already on an upward trend having grown 17% to $49.6 million during the second quarter of this year.

Still, Fosrenol is facing more competition in Europe after Genzyme received the regulatory nod to market its next-generation phosphate binder Renvela (sevelamer carbonate) back in June. And Shire’s stock remained depressed after the data failed to counter a downgrade by UBS analysts from ‘buy’ to ‘neutral’.