An intravenous formulation of Wyeth and Progenics Pharmaceuticals’s investigational drug Relistor has failed to make the grade in a late-stage trial in post-operative ileus but a Phase II study shows a lot of promise for an oral form of the drug to treat constipation.

The firms said a Progenics-conducted Phase III study of an IV formulation of Relistor (methylnaltrexone) for patients with post-operative ileus did not meet the primary or secondary end points, confirming the earlier findings of the Wyeth late-stage trial announced in March. The two companies said they will now think about “whether and how to continue development of this formulation of Relistor and this indication”.

However a Phase II study of an oral formulation of the drug for the treatment of opioid-induced constipation showed positive activity. The trial assessed the effects of a once-daily formulation of Relistor on 122 patients with chronic, non-malignant pain who were receiving opioids for pain management and it showed “statistically significant activity in treating the constipation as assessed by occurrence of spontaneous bowel movements and other efficacy measures”, the companies said. The formulation was also well-tolerated.

Wyeth’s chief medical officer Gary Stiles said that the firms are committed to continuing to develop the Relistor franchise to help address “the unmet medical needs of patients suffering from the gastrointestinal side effects of opioids”. Following the results from a second Phase II trial of another oral formulation, expected in a few months, Wyeth and Progenics “will further define the continued development plan for oral Relistor”, he added.

Last month, the US Food and Drug Administration approved Relistor as a subcutaneous injection for the treatment of OIC in patients with advanced illness who are receiving palliative care, when response to laxative therapy has not been sufficient. Noting that use of the treatment beyond four months has not been studied, Wyeth expects to make subcutaneous Relistor available in the USA in early June.

The latter has also been approved in Canada and the two firms received a positive opinion from the Committee for Medicinal Products for Human Use, the European Medicines Agency’s scientific committee, in April.