Introduction
Hydroxychloroquine (HCQ) was one of the first treatments used for
Covid-19 since studies showed promising results [1]–[3].
Nevertheless, later studies did not demonstrate any benefits with HCQ in
Covid-19 treatment, and, finally, its use declined all over the world
[4],[5].
HCQ is an antimalarial drug derived from quinolone that is safer than
chloroquine [6]. With a complex mechanism of action, it has also
immunosuppressive effects and is used for arthritis rheumatoid and lupus
erythematosus treatment [7]. The most frequent drug adverse effects
(ADR) of HCQ include headache, appetite disorders, ocular disturbances
– with retinopathies and ophthalmoplegia being the most serious ones -;
and gastrointestinal disorders. Serious known ADRs include
agranulocytosis, convulsions, deafness, cardiomyopathy, serious skin
reactions (i.e. Stevens-Johnson syndrome), myopathy, and suicidal
ideation, with the latter being identified during the Covid-19 pandemic.
Many of these ADRs are dose dependent and, because HCQ has a narrow
therapeutic window, caution is required. Moreover, HCQ can interact with
several other drugs. These interactions may be pharmacokinetic or
pharmacodynamic in nature. Because polypharmacy is common in elderly
patients and HCQ is usually administered more frequently in this
population, it is likely that drug-drug interactions contribute to the
ADR risk increment [8]. Altogether, these factors may have changed
HCQ safety profile as known before the Covid-19 pandemic outburst.
The aim of this study was to compare ADR cases related to HCQ when used
for Covid-19 treatment with cases in other indications as reported to
the Spanish Pharmacovigilance System (SEFV-H).