The National Institutes of Health said Saturday that it had stopped two clinical trials of hydroxychloroquine, the malaria drug that President Trump promoted to treat and prevent the coronavirus, one because the drug was unlikely to be effective and the other because not enough patients signed up to participate.
The agency halted a trial that had aimed to enroll more than 500 patients after an independent oversight board determined that the drug did not appear to benefit hospitalized patients. The same day, the N.I.H. said it had closed another trial — of hydroxychloroquine and the antibiotic azithromycin — because only about 20 patients had enrolled in the planned study of 2,000 people.
The two trials the N.I.H. shut down represent the latest evidence that hydroxychloroquine has not lived up to its early promise of fighting the coronavirus.
The N.I.H. said Saturday that an independent oversight board that monitors safety met