Shares in the USA’s CV Therapeutics have plunged over 20% following the news that the firm’s angina drug Ranexa was shown to be ineffective in treating patients with acute coronary syndrome.

Despite the disappointing results from an analysis of unblended data, CV added that there was no adverse death trend or arrhythmias in the 6,500-patient study, which was designed to evaluate the efficacy and safety of Ranexa (ranolazine) during acute and long-term treatment. The firm added that it still believes the data could support expansion of the existing Ranexa indication to include first line angina.

Ranexa, which got the green light from the US Food and Drug Administration at the beginning of last year, is currently approved to treat chronic angina in patients who have not responded well to other such treatments and is used in combination with other drugs such as amlodipine, beta-blockers or nitrates.

The drug is vital to CV’s success but there are concerns about future growth for Ranexa purely in the cardiology setting. Deutsche Bank downgraded the stock from ‘buy’ to ‘hold’ because the treatment has failed to show clear efficacy as a first-line agent and despite a reasonable safety profile, the lack of efficacy supporting benefit in acute coronary syndrome could translate to “questionable utility” as a persistent angina treatment.

However analysts at Piper Jaffray issued a note saying that despite Ranexa's disappointing results, the drug could show promise in the diabetes market. "With cardiovascular efficacy questions now addressed, our key remaining question…is whether Ranexa causes a significant reduction in glucose levels in diabetics. We have historically viewed and continue to view the diabetes data as a possible game changer for Ranexa," they added.