Toxicity of chloroquine and hydroxychloroquine following therapeutic use or overdose

Introduction: While chloroquine, a derivative of quinine, has been used as an antimalarial for 70 years, hydroxychloroquine is now used to treat conditions such as rheumatoid arthritis and systemic lupus erythematosus. In 2020, hydroxychloroquine (and to a lesser extent chloroquine) also received attention as a possible treatment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). During investigation for treating coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2, concerns for serious adverse events arose.

Objective: We review the toxicity associated with hydroxychloroquine and chloroquine use both short-term and long-term and in overdose.

Methods: Medline (via OVID) was searched from its inception through June 7 2020 using the following as either MeSH or keyword terms: ("Chloroquine/" or "Hydroxychloroquine/") AND ("Adverse Drug Event/" or "Toxicities, Drug/" or "Toxic.mp." or "Toxicity.mp." or "Overdose.mp."). We limited resultant articles to those published in English and reporting on Human subjects. This search yielded 330 articles, of which 57 were included. Articles were excluded due to lack of relevance, not reporting desired outcomes, or being duplicative in their content. Twenty-five additional articles were identified through screening references of included articles. To identify toxicities in individuals treated with hydroxychloroquine or chloroquine with COVID-19, we searched PubMed on June 10th, 2020: ("Chloroquine" or "Hydroxychloroquine") AND ("Coronavirus" or "COVID-19" or "SARS-CoV-2"). This search resulted in 638 articles. We reviewed articles for reporting of adverse events or toxicities. Most citations were excluded because they did not include original investigations or extrapolated data from subjects that did not have COVID-19; 34 citations were relevant. For the drug-interactions section, relevant classes and agents were identified through a screen of the https://www.covid19-druginteractions.org/ website. We then conducted targeted searches of PubMed up to June 7th 2020 combining "chloroquine" and "hydroxychloroquine" with terms for specific drug classes and drugs identified from the drug-interaction site as potentially relevant. We found 29 relevant articles.

Toxicity with short-term use: Gastrointestinal: Gastrointestinal toxicities are the most common to occur following initiation of chloroquine or hydroxychloroquine. Nausea, vomiting, and diarrhea account for most reported intolerances. Glucose abnormalities: Alterations in blood glucose concentrations may occur with hydroxychloroquine but are rare with standard therapeutic use. Cardiotoxicity: Short-term use can produce conduction abnormalities. Evidence from COVID-19 treatment suggests QT/QTc prolongation is of concern, particularly when used in combination with azithromycin, although disagreement exists across studies. Dermatologic: Drug eruptions or rashes, followed by cutaneous hyperpigmentation, pruritis, Stevens-Johnson syndrome, and toxic epidermal necrolysis, may occur within days to weeks of exposure but usually resolve with the discontinuation of therapy. Neuropsychiatric: Reported symptoms include confusion, disorientation, and hallucination within 24-48 h of drug initiation. Other toxicities: Hemolysis and anemia may occur in patients with glucose-6-phosphate dehydrogenase. Chloroquine treatment of COVID-19 was associated with elevation in creatine kinase and creatine kinase-MB activities with more events in the higher-dose group.

Toxicity with long-term use: Retinopathy: Retinopathy is the major dose-limiting toxicity associated with long-term use; the risk is higher with increasing age, dose, and duration of usage. Cardiotoxicity: Long-term use has been associated with conduction abnormalities, cardiomyopathy, and valvular disorders. Neurotoxicity: Rarely myositis and muscle weakness, extremity weakness, and pseudoparkinsonism have been reported.

Toxicity in overdose: Symptoms in overdose manifest rapidly (minutes to hours) and cardiotoxicity such as cardiovascular shock and collapse are most prominent. Neurotoxic effects such as psychosis and seizure may also occur.

Conclusions: Hydroxychloroquine is a generally well-tolerated medication. Short-term (days to weeks) toxicity includes gastrointestinal effects and rarely glucose abnormalities, dermatologic reactions, and neuropsychiatric events. Cardiotoxicity became of increased concern with its use in COVID-19 patients. Long-term (years) toxicities include retinopathy, neuromyotoxicity, and cardiotoxicity (conduction abnormalities, cardiomyopathy). Deaths from overdoses most often result from cardiovascular collapse.

Keywords: COVID-19; Coronavirus; chloroquine; hydroxychloroquine; toxicity.