Antimalarial / DMARD Pregnancy: First-trimester exposure at doses higher than usual rheumatological doses suggests a small increase in relative risk of congenital malformations (RR 1.33 for >=400 mg/day; 0.95 for 400 mg/day). In SLE and antiphospholipid syndrome the balance of benefit outweighs potential harm and it should be continued (consider a dose below 400 mg if sufficiently effective). Excreted in small amounts in breast milk (~1-3% of adult dose); low risk to the infant, with a careful benefit-risk assessment.

Hydroxychloroquine sulfate

Brand names: Plaquenil

Hydroxychloroquine sulfate is the salt form supplied in UK tablets of hydroxychloroquine, a disease-modifying antirheumatic drug used for rheumatoid arthritis and lupus erythematosus and as an antimalarial.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 400 mg

Route: Oral

Frequency: Initially 400 mg daily in divided doses

Max: 6.5 mg/kg/day (calculated from ideal body weight, not actual body weight); daily dose 200 mg, 300 mg or 400 mg

SPC for the 200 mg film-coated tablet. Adults (including the elderly): use the minimum effective dose, not exceeding 6.5 mg/kg/day based on ideal body weight (using absolute body weight could cause overdose in the obese). In patients able to receive 400 mg daily: initially 400 mg daily in divided doses; reduce to 200 mg when no further improvement is evident; increase maintenance to 300 mg or 400 mg daily if response lessens. Take each dose with a meal or glass of milk; cumulative in action (several weeks to benefit). For rheumatic disease, discontinue if no improvement by 6 months. Paediatric use: minimum effective dose not exceeding 6.5 mg/kg/day based on ideal body weight; the 200 mg tablet is not suitable for children with ideal body weight below 31 kg - verify paediatric dosing against a children's formulary. More frequent retinopathy monitoring if daily dose exceeds 6.5 mg/kg lean body weight, renal insufficiency, visual acuity below 6/8, age >65 years, or cumulative dose >200 g.

Dose adjustments

Renal

Use with caution in renal disease; renal insufficiency warrants more frequent retinopathy monitoring. Estimate plasma hydroxychloroquine levels in patients with severely compromised renal function and adjust dose accordingly.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to hydroxychloroquine or to any of the excipients
Known hypersensitivity to 4-aminoquinoline compounds
Pre-existing maculopathy of the eye

Side effects

Blurring of vision due to a dose-dependent, reversible disturbance of accommodation (common)
Abdominal pain, nausea (very common); diarrhoea, vomiting (common)
Skin rash, pruritus (common); pigmentary disorders of skin/mucous membranes, bleaching of hair, alopecia (uncommon)
Headache (common); dizziness (uncommon)
Retinopathy with pigmentation changes and visual field defects (uncommon); maculopathy/macular degeneration (not known, may be irreversible)

Interactions

Other QT-prolonging or arrhythmogenic drugs: not recommended concomitantly (hydroxychloroquine prolongs the QT interval, increasing risk of ventricular arrhythmias) [US label]
Azithromycin or other macrolide antibiotics: carefully weigh benefits/risks before prescribing, because of potential increased risk of cardiovascular events and mortality
Insulin or other antidiabetic drugs: effects may be enhanced, increasing hypoglycaemic risk; a dose reduction of the antidiabetic may be needed [US label]
Drugs that lower the seizure threshold (e.g. mefloquine): may increase risk of seizures [US label]
Antiepileptic drugs: activity may be impaired if co-administered [US label]

Clinical monograph

How it works

It raises lysosomal pH and modulates immune cell function—impairing antigen presentation and Toll-like receptor signalling—to reduce inflammatory activity in autoimmune disease.

Prescribing in practice

Irreversible retinal maculopathy is the key long-term hazard, so use weight-based dosing, arrange baseline and ongoing retinal screening per Royal College of Ophthalmologists guidance, and report any visual change.
It may prolong the QT interval and, rarely, cause cardiomyopathy, so use caution alongside other QT-prolonging drugs and in cardiac disease.
Use caution in G6PD deficiency, hepatic or renal impairment, and psoriasis (which it may worsen).

Monitoring

Perform retinal screening as recommended, watch for visual disturbance, and review cardiac, hepatic and renal status where clinically relevant.

Counselling the patient

Keep your eye-check appointments and report any blurring or changes in colour vision.
The benefit builds gradually over weeks to months, so take it consistently.
Store safely away from children because overdose can be life-threatening.

Evidence & guidelines

Hydroxychloroquine sulfate is the established UK salt form, with efficacy and the retinopathy screening framework documented in the SPC, NICE guidance and Royal College of Ophthalmologists recommendations.

Reference: NICE NG100 (RA); RCOphth/BSR retinopathy screening guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways