Hydroxychloroquine Dose Calculator

Hydroxychloroquine (HCQ) is an antimalarial and immunomodulatory drug widely used in the management of autoimmune conditions including systemic lupus erythematosus (SLE), rheumatoid arthritis, and discoid lupus. It is also used for malaria prophylaxis and treatment. Because hydroxychloroquine has a narrow therapeutic window — particularly with respect to retinal toxicity — accurate dosing based on patient-specific parameters is essential to maximise clinical benefit while minimising the risk of adverse effects. Two dosing methods are commonly used in clinical practice. Weight-based dosing calculates the daily dose by multiplying the patient's body weight in kilograms by a prescribed dose per kilogram (typically 5 mg/kg/day for most adult autoimmune indications). Body surface area (BSA)-based dosing is sometimes preferred for paediatric patients or when more precise body size adjustment is needed; it uses the Mosteller formula to calculate BSA as the square root of [Height (cm) × Weight (kg) / 3600], and then multiplies BSA by a prescribed dose per square metre (commonly 200 mg/m²/day). In both methods, the calculated dose is capped at the maximum safe daily dose — most guidelines recommend a ceiling of 400 mg/day for adults, though this may be adjusted downward (to 5 mg/kg/day or less of ideal body weight) in patients with reduced renal function or those at elevated risk of retinal toxicity. Retinal toxicity is the most serious long-term risk of hydroxychloroquine and is dose-dependent and cumulative. Exceeding the recommended daily dose accelerates the accumulation of HCQ in retinal tissue, increasing the risk of bull's-eye maculopathy — a pattern of retinal damage that can lead to irreversible central vision loss. The American Academy of Ophthalmology recommends annual retinal screening after five years of use, or earlier in patients with additional risk factors such as renal impairment, tamoxifen use, or pre-existing retinal disease. For weight-based dosing, the standard starting dose for lupus is 200–400 mg/day, not to exceed 5 mg/kg/day of actual body weight (or ideal body weight in obese patients, per updated guidance). For paediatric patients, doses up to 6.5 mg/kg/day have been used but should always be checked against the maximum absolute daily dose. BSA-based dosing at approximately 200 mg/m²/day provides an alternative calculation that naturally scales with body size, which can be particularly useful in growing children. This calculator is intended as a clinical decision support tool and does not replace professional medical judgment. Always verify the calculated dose against current prescribing guidelines, the patient's renal function, and any other relevant clinical factors. Consult a rheumatologist, paediatrician, or pharmacist before initiating or adjusting hydroxychloroquine therapy.