A Case Series and Review of Hydroxychloroquine Toxicity and Monitoring: How Do We Dose Hydroxychloroquine?

Hydroxychloroquine (HCQ) is an anti-malarial drug safely used in rheumatologic conditions with its various mechanisms on immunomodulation aside from its impact on cardiovascular health. However, multiple systemic effects, from ocular toxicity to cardiotoxicity, were reviewed and reported within adequate weight-based HCQ doses, challenging the need for alternate HCQ monitoring. We report cases with catastrophic adverse events from chronic HCQ use and supratherapeutic blood HCQ levels while within the recommended weight-based dosing. Cases of supratherapeutic HCQ blood levels have emerged despite adherence to weight-based dosing, indicating the necessity for individualized monitoring. This study aims to highlight the toxicities associated with chronic HCQ use along with the limitations of current weight-based dosing guidelines. This also provides a discussion on the unique pharmacokinetics and pharmacodynamics of HCQ in better understanding proposed HCQ blood level monitoring.