The US FDA has launched an investigation into the safety of Boehringer Ingelheim's Parkinson's disease drug Mirapex after becoming concerned it may be linked to an increased risk of heart failure.
The regulator stressed that its probe should not prompt patients to discontinue therapy with Mirapex (pramipexole), a dopamine agonist that treats Parkinson's and is also approved for moderate-to-severe restless legs syndrome.
The reason for the FDA's concern is a pooled analysis of randomised phase II and III clinical trials of Mirapex - sold as Sifrol in Europe - which found that heart failure was more frequent with Boehringer's drug than placebo, although the difference was not statistically significant
Two epidemiological studies also found a difference between the drug and placebo in terms of onset of heart failure.
Specifically, the agency evaluated studies filed in 2008 and updated in 2010 which found 12 cases of newly-diagnosed heart failure among 4,157 patients taking Mirapex, and four cases of out 2,820 receiving placebo.
As there was an indication that the rate may be higher with drug treatment, Boehringer sponsored an epidemiological study using the UK's General Practice Research Database (GPRD) which found that patients who used a dopamine agonist were significantly more likely to develop heart failure than those who did not.
After drilling down in the data to look at individual products, the study indicated a significant increase in risk for Mirapex and another dopamine agonist called cabergoline, which is marketed by Pfizer as Dostinex. However, a second epidemiological study failed to reproduce that finding.
Faced with conflicting data the agency has decided to start an official probe and said it is "continuing to work with the manufacturer to clarify further the risk of heart failure with Mirapex and will update the public when more information is available".
Mirapex is a former blockbuster drug for Boehringer but has assumed less importance for the company in recent years after patent expiries in key markets, including the US in 2010 when its worldwide turnover was round €670m.