BANGALORE (Reuters) - U.S. health regulators said they are reviewing the safety of GlaxoSmithKline's anti-nausea drug Zofran to ascertain whether there is a potential risk of abnormal heart rhythm.

The drug may increase the risk of developing abnormal changes in the electric activity of the heart, leading to a potentially fatal heart rhythm, the U.S. Food and Drug Administration said in a statement.

GSK will be required to conduct a study on whether Zofran could prolong a patient's QT interval, a measure of heart rhythm. The results of the study are expected in summer of 2012.

In the meanwhile, the FDA said it was making interim changes to the drug's labels to include a warning that Zofran be avoided in patients with congenital long QT syndrome.