Hydroxychloroquine, often recognized by the brand name Plaquenil, is primarily an antimalarial drug with immunomodulatory properties. This dual functionality makes it useful for treating various conditions. This article focuses on how hydroxychloroquine dosage is determined and the factors that influence it.
Conditions Treated and Typical Dosing
Hydroxychloroquine treats and prevents malaria, particularly where chloroquine resistance is not reported. For prevention, adults take 400 mg (310 mg base) orally once weekly, starting one to two weeks before travel and continuing for four weeks after. Children weighing 31 kg or more take a weekly dose of 6.5 mg/kg, not exceeding the adult dose.
For active malaria, adult dosing is more intensive. An initial 800 mg (620 mg base) dose is followed by 400 mg (310 mg base) at 6, 24, and 48 hours, totaling 2000 mg (1550 mg base). Children weighing 31 kg or more receive an initial 13 mg/kg (up to 800 mg), followed by 6.5 mg/kg (up to 400 mg) at 6, 24, and 48 hours.
Hydroxychloroquine is a disease-modifying anti-rheumatic drug (DMARD), a first-line treatment for systemic lupus erythematosus (SLE), and a second-line treatment for rheumatoid arthritis (RA). It interferes with immune cell communication, reducing inflammation. For these conditions, the adult dose ranges from 200 mg to 400 mg daily, often taken once or in two divided doses.
For rheumatoid arthritis, the initial daily dose is 400 mg to 600 mg, taken once or in two divided doses. Once a response is achieved, the dosage may be reduced by 50% to a maintenance dose of 200 mg to 400 mg daily. For systemic lupus erythematosus, the dose is 200 mg to 400 mg daily, administered once or divided. Doses exceeding 400 mg daily are not recommended for SLE.
Beyond RA and SLE, hydroxychloroquine treats discoid lupus erythematosus (DLE) and sometimes Sjögren’s syndrome. Dosing for DLE is 200 mg to 400 mg daily, similar to SLE. Research on Sjögren’s syndrome did not show significant clinical benefit.
Factors Influencing Hydroxychloroquine Dose
Hydroxychloroquine dose determination involves several physiological and medical factors for effectiveness and safety. Body weight is significant; the dose is calculated based on ideal body weight to minimize toxicity, especially ocular adverse reactions. The maximum recommended dose is 5 mg/kg per day, not exceeding 400 mg daily for most indications.
Kidney function plays a role in dose adjustment. Since kidneys clear the drug, impaired function can lead to drug accumulation, necessitating a reduced dose. For patients with an estimated glomerular filtration rate (eGFR) below 30 ml/min per 1.73 m², the dose should be reduced by 25%.
Liver function is another consideration, though dose modifications due to impairment are less common than for kidney issues. Severe liver impairment might still require dose adjustment to prevent excessive drug levels. Disease activity and individual response influence dosage, allowing doctors to adjust based on condition control and therapeutic effects.
Age is a factor, with specific considerations for pediatric and elderly patients. Hydroxychloroquine can be prescribed to children for malaria prevention and treatment, though not recommended for those weighing less than 31 kg for certain formulations. Elderly patients may have age-related kidney, liver, or heart issues, requiring caution and dose adjustments.
Important Considerations When Dosing
A significant dose-related side effect of hydroxychloroquine is retinopathy, affecting the retina. The risk of irreversible sight loss increases with higher daily doses (above 5 mg/kg per day) and longer use, especially after five years. To mitigate this, baseline ophthalmological exams are recommended before or within the first year of therapy.
Regular retinal imaging is advised annually after five years of therapy for most patients. More frequent screening may be suggested for individuals with additional risk factors, including tamoxifen use, impaired renal function, or a daily dose exceeding 5 mg/kg. Patients should report any visual changes to their healthcare provider immediately.
Inform healthcare providers about all other medications, supplements, and herbal products due to potential drug interactions. Hydroxychloroquine can interact with certain drugs, potentially increasing their levels or altering effects. For example, interactions with anticoagulants could increase bleeding risk.
Patients should take hydroxychloroquine exactly as prescribed. If a dose is missed, take it as soon as remembered unless it is almost time for the next dose; doubling up is not advised. Overdosing can be dangerous and requires immediate medical attention. Adherence to the prescribed regimen is important, as non-adherence links to a higher risk of disease flares and hospitalizations in conditions like lupus.