The Food and Drug Administration placed a partial hold on a study involving diabetes drug Avandia by barring new patients from enrolling in the trial with known safety risks.

The clinical study called TIDE is organized to compare GlaxoSmithKline PLC's Avandia with Actos, a similar diabetes drug by Takeda Pharmaceutical Co. The main focus of the study is to compare the cardiovascular risks of the two drugs that are used to lower blood-glucose levels in diabetic patients.

Avandia was once the world’s best-selling diabetes drug, until an analysis found in 2007 that patients taking the drug had a 43 percent increase in heart attack risks.

The number of patients taking Avandia has dropped in recent years. From 13 million prescriptions written in 2006 at its peak, the number declined to about 2.6 million, according to IMS Health, a pharmaceutical market research company.

Last week, a FDA panel voted to keep the controversial drug on the market but recommended for tighter supervision and additional warnings on the label.

The FDA’s drug-safety officer David Graham stated that Avandia study is unethical because it presents patients a drug with known safety risks.

The FDA said on Wednesday that no new patients may be enrolled into the study and current trial participants need to be given an updated informed consent forms. The FDA further instructed Glaco to send the new safety information from the FDA panel meeting to TIDE investigators, institutional review boards and ethics committees.