Just a few reasons to be careful rather than believing conspiricies to ban hydroxychloroquine.
QT interval prolongation
Hydroxychloroquine can cause prolonged QT interval which may lead to arrhythmia and ventricular tachycardia.6On 24 April 2020 the US Food and Drug Administration (FDA) issued a caution against the use of hydroxychloroquine or chloroquine for COVID-19 outside of the hospital setting or clinical trial due to the risk of adverse effects on heart rhythm.7
Common adverse effects
Common (> 1%) adverse effects of hydroxychloroquine include nausea, vomiting, anorexia, abdominal cramps, rash, itch, alopecia and headache.3 Hydroxychloroquine reduces HbA1c and there are reports of severe hypoglycaemia, although the frequency of these effects is unknown.3,6
Toxicity from prolonged exposure
According to the literature, the main toxicological adverse effects from prolonged exposure to hydroxychloroquine in approved conditions include:3,6,8 retinopathy (see ocular effects below)cardiac toxicity (see cardiac effects below)neuromyopathy as evidenced by abnormal nerve conduction and sensory changes. This is infrequent (0.1%–1%).3
Cardiac effects
Although rare (< 0.1%), cardiotoxic effects can include cardiomyopathy and conduction disorders.3,6Chronic cardiotoxicity should be considered when conduction disorders such as bundle branch block/ atrioventricular (AV) block or biventricular hypertrophy are diagnosed.3,6 Clinical monitoring for signs and symptoms of cardiomyopathy is advised.6 Hydroxychloroquine prolongs the QT interval and the magnitude of this effect may increase with increasing concentrations of the drug.6 See ‘What about interactions with other medicines?’ below.
Ocular effects
As well as blurred vision, which is a common adverse effect,3 other serious ocular effects include:3,6reversible corneal changes – oedema and opacities have been known to occur from 3 months to some years after commencing therapy 6 retinopathy with changes in pigmentation and visual field defects – can progress to irreversible vision loss as daily dose and duration of treatment increase3maculopathies and macular degeneration that may be irreversible.6In addition to increasing daily doses (> 5 mg/kg actual weight) and long-term use (> 5 years), major risk factors for retinopathy include:9renal disease (eGFR < 60 mL/min/1.73m2)concomitant tamoxifen use.
Even at therapeutic doses for indicated conditions (Table 1) baseline ocular examination is recommended within the first 6–12 months of treatment, followed by regular screening.3,9,10 in the absence of specific risk factors, monitoring is not required for the first 5 years, after which annual monitoring is recommended.9
What about interactions with other medicines?
Hydroxychloroquine is thought to be incompatible with monoamine oxidase inhibitors (MAOIs).3,6Because hydroxychloroquine prolongs the QT interval it should not be used by patients receiving other medicines known to prolong the QT interval eg, Class IA and III antiarrhythmics, tricyclic antidepressants, antipsychotics and some antibiotics, including azithromycin, due to increased risk of ventricular arrhythmia.3,6,11See What's next in clinical trials?
Other medicines that interact with hydroxychloroquine include antidiabetic agents, other antimalarial agents known to lower convulsion threshold (eg, mefloquine), digoxin and some antiepileptic medicines.6Tamoxifen is contraindicated due to its own retinal toxicity.3,6
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