FDA now wants chloroquine limited to hospitals and clinical trials [UPDATED]

Enlarge / Hospital Corpsman 3rd Class Kimberly Wyss, from Ventura, Calif., dons surgical gloves aboard the hospital ship USNS Mercy (T-AH 19). (credit: flickr)

Update, April 24: On Friday, the FDA issued a safety announcement regarding the use of hydroxychloroquine or chloroquine, saying the drugs' use "should be limited to clinical trial settings or for treating certain hospitalized patients." The move came in response to a growing number of "adverse incident" reports from hospitals and outpatient treatment, focused on a known side effect of chloroquine and its derivatives: changes in heart rhythm that can be (and apparently have been) fatal.

Chloroquine is know to alter a property of the heart's electrical activity called the QT interval. Should this interval get overly long, the heart can lose its rhythm entirely; if the lower chambers stop coordinated contractions, the results are fatal unless they can be restarted. One anecdotal report of successful treatment of COVID-19 had paired chloroquine with the antibiotic azithromycin, which also prolongs the QT interval, which led to the drugs frequently being prescribed together.

By limiting the use of the drug to hospital settings, the FDA is attempting to ensure appropriate care is available should the side effects become problematic. The adverse effect reports it cites indicates that, while there were some fatalities, there are also non-fatal cases of the potentially lethal ventricular fibrillation, which suggests availability of medical staff allowed these patients to recover.

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