Chloroquine, hydroxychloroquine and COVID-19

The media have featured the antimalarials chloroquine (CQ) and hydroxychloroquine (HCQ) to treat coronavirus (COVID-19). Political leaders have touted their use and recommended availability to the public. These anti-inflammatory agents have substantial human toxicity with a narrow therapeutic window. CQ and HCQ poisoning cause myocardial depression and profound hypotension due to vasodilation. Bradycardia and ventricular escape rhythms arise from impaired myocardial automaticity and conductivity due to sodium and potassium channel blockade. With cardiotoxicity, ECGs may show widened QRS, atrioventricular heart block and QT interval prolongation. CQ may also cause seizures, often refractory to standard treatment. Of concern is pediatric poisoning, where 1-2 pills of CQ or HCQ can cause serious and potentially fatal toxicity in a toddler. The treatment of CQ/HCQ poisoning includes high-dose intravenous diazepam postulated to have positive ionotropic and antidysrhythmic properties that may antagonize the cardiotoxic effects of CQ. Infusions of epinephrine titrated to treat unstable hypotension, as well as potassium for severe hypokalemia may be required. Current scientific evidence does not support treatment or prophylactic use of these agents for COVID-19 disease. Regulatory and public health authorities recognize that CQ/HCQ may offer little clinical benefit and only add risk requiring further investigation before wider public distribution.