Ardelyx shares were down near 30% in late-afternoon trading Monday after it emerged that its investigational kidney disease drug tenapanor was linked with high rates of diarrhoea in mid-stage trials.

While the drug, which is partnered with AstraZeneca, hit Phase II targets in significantly decreasing serum phosphate levels in patients with chronic kidney disease, the rate of diarrhoea was “distinctly higher than expected”, the firm said.

Alarm bells are now ringing as “diarrhoea can be an issue in this patient population because fluid levels are important for these patients,” Wedbush analyst David Nierengarten told Reuters.

Ardelyx said it would now work with AstraZeneca, which licensed tenapanor in October 2012, to evaluate the future development plans for the drug.