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).