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Aminoquinoline — Malaria Prophylaxis / SLE / Rheumatoid Arthritis Pregnancy: VERBATIM (eMC §4.6): a population-based cohort of 2045 hydroxychloroquine-exposed pregnancies 'suggests a small increase in the relative risk (RR) of congenital malformations associated with hydroxychloroquine exposure in the first trimester (n = 112 events) at doses higher than those normally used in rheumatological conditions. For a daily dose of ≥ 400 mg the RR was 1.33 (95% CI, 1.08 - 1.65). For a daily dose of < 400 mg the RR was 0.95 (95% CI, 0.60 - 1.50).' In lupus and antiphospholipid syndrome 'the balance of benefit outweighs any potential harm to the foetus and therefore HCQ should be continued. A dose below 400mg should be considered if thought sufficiently effective by the physician.' In other diseases the prescriber should assess the risk/benefit ratio. Available evidence does not show an increased risk of retinal toxicity in infants after maternal therapy. Lactation: limited data, no harmful effects observed, small amounts excreted in breast milk (estimated infant exposure <1% to about 3% of the adult dose); make a careful benefit-risk assessment. US label risk summary: 'Prolonged clinical experience over decades of use and available data from published epidemiologic and clinical studies with hydroxychloroquine sulfate tablets use in pregnant women have not identified a drug-associated risk of major birth defects, miscarriage, or adverse maternal, or fetal outcomes', and it notes there are risks to mother and fetus from untreated or increased disease activity from malaria, rheumatoid arthritis and SLE, plus a pregnancy exposure registry (1-877-311-8972). Fertility: no information on human fertility; chloroquine showed adverse effects on male fertility in animal studies.

Hydroxychloroquine

Brand names: Plaquenil

Hydroxychloroquine is an antimalarial that is also used as a disease-modifying agent in rheumatoid arthritis and systemic lupus erythematosus (SLE).

Adult dose

Dose: Malaria prophylaxis: 400 mg once a week
Route: Oral — administer with food or milk; do not crush or divide the tablets
Frequency: Once a week on the same day every week: begin 2 weeks before travel to the endemic area, continue the same weekly dose while in the endemic area, and continue weekly for 4 weeks after leaving
SCOPE — READ FIRST: this is MALARIA PROPHYLAXIS, the page's primary infectious-disease indication and route, taken from the US label because the UK SPC in this bundle contains no malaria regimen. VERBATIM (openFDA §2.2): 'The recommended prophylaxis dosage is: Adult patients: 400 mg once a week. Pediatric patients ≥ 31kg: 6.5 mg/kg actual body weight (up to 400 mg) once a week.' 'Treatment must start 2 weeks before travel to an endemic area. Advise the patient to take the prophylaxis dosage once a week, staring 2 weeks prior to travel to the endemic area, on the same day every week, continuing the same weekly dose while in the endemic area, and for 4 weeks after leaving the endemic area.' TREATMENT OF UNCOMPLICATED MALARIA is a different indication in the same label, for reference only: 'Adult patients: Administer 800 mg initially; subsequently administer 400 mg at 6 hours, 24 hours, and 48 hours after the initial dose (total dosage = 2000 mg)', and 'For radical cure of P. vivax and P. ovale infections, concomitant therapy with an 8-aminoquinoline drug is necessary.' RESISTANCE: §8.4 establishes paediatric effectiveness only 'for the prophylaxis of malaria in geographic areas where chloroquine resistance is not reported'. This bundle contains NO country-by-country malaria risk or resistance data, so check current UK travel-health guidance before prescribing. RHEUMATOLOGICAL DOSING IS DIFFERENT AND MUST NOT BE CONFUSED WITH THE WEEKLY PROPHYLAXIS DOSE: US label rheumatoid arthritis initial 400 mg to 600 mg daily, chronic 200 mg to 400 mg daily; SLE and chronic discoid lupus 200 mg once daily or 400 mg once daily or in two divided doses; UK SPC 'This dose should not exceed 6.5/kg/day (calculated from ideal body weight) and will be either 200mg, 300mg or 400mg per day.' The only ceilings anywhere in this bundle are those per-kg DAILY limits for the rheumatological indications, so no maxDose is published for the weekly prophylaxis dose. COVID-19 is not addressed anywhere in this bundle. Some sections of the product information we used were incomplete — check the full SPC.

Paediatric dose

Route: Oral — with food or milk; the tablets cannot be crushed or divided
Frequency: Once a week, beginning 2 weeks before travel and continuing for 4 weeks after leaving the endemic area
Max: 400 mg once a week (the weekly prophylaxis dose is capped at the adult dose)
dosePerKg is DELIBERATELY null: the weekly prophylaxis dose of 6.5 mg per kg applies ONLY to children of 31 kg or more, so it is not valid across the paediatric range and must not be fed to a weight calculator that has no lower weight limit. VERBATIM (openFDA §2.2): 'Pediatric patients ≥ 31kg: 6.5 mg/kg actual body weight (up to 400 mg) once a week' and 'Hydroxychloroquine sulfate tablets are not recommended in pediatric patients less than 31 kg because the lowest available strength (200 mg) exceeds the recommended dose for these patients and it cannot be divided.' TREATMENT OF UNCOMPLICATED MALARIA in children ≥ 31 kg, a different indication: '13 mg/kg (up to 800 mg) initially; subsequently administer 6.5 mg/kg (up to 400 mg) at 6 hours, 24 hours, and 48 hours after the initial dose (total dosage = 31 mg/kg - up to 2000 mg).' The UK SPC adds that 'The 300mg tablet is therefore not suitable for use in children with an ideal body weight of less than 46kg' and that the paediatric dose 'should not exceed 6.5mg/kg/day based on ideal body weight'. Note the prophylaxis figure is on ACTUAL body weight while the UK daily ceiling is on IDEAL body weight. Verify any under-18 dose against a children's formulary and current UK travel-health guidance.

Dose adjustments

Renal

eMC §4.4: use with caution in 'patients with hepatic or renal disease, and in those taking drugs known to affect those organs. Estimation of plasma hydroxychloroquine levels should be undertaken in patients with severely compromised renal or hepatic function and dosage adjusted accordingly.' Impaired renal function (estimated glomerular filtration rate of less than 60 ml/min/1.73m2) is also listed as a retinopathy risk factor, and such patients 'should be referred for retinopathy monitoring once they have been taking the medication for 1 year' rather than 5 years. US label: hydroxychloroquine is substantially excreted by the kidney and the risk of toxic reactions may be greater in renal impairment; consider phospholipidosis as a possible cause of renal injury in patients with underlying connective tissue disorders and discontinue if renal toxicity is suspected or demonstrated by tissue biopsy. NO NUMERIC dose reduction is given in either label.

Hepatic

eMC §4.4: use with caution in 'patients with hepatic or renal disease, and in those taking drugs known to affect those organs. Estimation of plasma hydroxychloroquine levels should be undertaken in patients with severely compromised renal or hepatic function and dosage adjusted accordingly.' The US label additionally reports hepatotoxicity in patients with porphyria cutanea tarda and advises avoiding hydroxychloroquine in porphyria. NO NUMERIC dose adjustment is given in either label.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Malaria in Adult and Pediatric Patients ( 2.2 ): ● Prophylaxis: Begin weekly doses 2 weeks prior to travel to the endemic area, continue weekly doses while in the endemic area, and continue the weekly doses for 4 weeks after leaving the endemic area: - Adults: 400 mg once a week - Pediatric patients ≥ 31 kg: 6.5 mg/kg up to 400 mg, once a week ● Treatment of Uncomplicated Malaria: See Full Prescribing Information (FPI) for complete dosing information. Rheumatoid Arthritis in Adults ( 2.3 ): Initial dosage: 400 mg to 600 mg daily Chronic dosage: 200 mg once daily or 400 mg once daily (or in two divided doses) Systemic Lupus Erythematosus in Adults ( 2.4 ): 200 mg once daily or 400 mg once …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-10-09. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

  • Known hypersensitivity to 4-aminoquinoline compounds (both the US label and the UK SPC)
  • Hypersensitivity to hydroxychloroquine or to any of the excipients listed in section 6.1 (UK SPC §4.3)
  • Pre-existing maculopathy of the eye (UK SPC §4.3)
  • US label warning rather than a formal contraindication: avoid in patients with psoriasis — worsening of psoriasis has been reported, and the UK SPC notes hydroxychloroquine may precipitate attacks of psoriasis
  • US label warning rather than a formal contraindication: avoid in patients with porphyria — hepatotoxicity was reported in patients with porphyria cutanea tarda
  • US label warning rather than a formal contraindication: not recommended in patients taking other drugs that prolong the QT interval or are arrhythmogenic.

Side effects

  • Gastrointestinal, very common: abdominal pain, nausea; common: diarrhoea, vomiting — usually resolving immediately on reducing the dose or stopping treatment
  • Eye, common: blurring of vision due to a disturbance of accommodation, dose dependent and reversible; uncommon: retinopathy with pigmentary changes and visual field defects, uncommon if the recommended daily dose is not exceeded, and corneal changes including oedema and opacities; frequency not known: maculopathies and macular degeneration (onset from 3 months to several years) which may be IRREVERSIBLE
  • Cardiac, frequency not known: QT interval prolongation in patients with specific risk factors, which may lead to arrhythmia (torsade de pointes, ventricular tachycardia); cardiomyopathy which may result in cardiac failure and in some cases a fatal outcome
  • Skin, common: rash, pruritus; uncommon: pigmentary disorders of skin and mucous membranes, bleaching of hair, alopecia; frequency not known: bullous eruptions including erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis, DRESS syndrome, Sweet's syndrome, photosensitivity, exfoliative dermatitis and acute generalised exanthematous pustulosis
  • Nervous system, common: headache; uncommon: dizziness; frequency not known: convulsions reported with this drug class, and extrapyramidal disorders such as dystonia, dyskinesia and tremor
  • Immune, frequency not known: urticaria, angioedema, bronchospasm
  • US label: haemolytic anaemia associated with G6PD deficiency; bone marrow depression, anaemia, aplastic anaemia, agranulocytosis, leukopenia, thrombocytopenia
  • US label: skeletal muscle myopathy or neuropathy; neuropsychiatric reactions including suicidality; hypoglycaemia; renal toxicity
  • Interactions to expect: hydroxychloroquine may enhance the effects of insulin and antidiabetic drugs and increase hypoglycaemic risk (a dose decrease of those drugs may be necessary); it lowers the seizure threshold, so co-administration with other antimalarials known to lower it, such as mefloquine, may increase seizure risk; the activity of antiepileptic drugs may be impaired

Monitoring

  • Retinopathy monitoring, verbatim (UK SPC §4.4): 'Patients who take hydroxychloroquine should be referred for annual retinopathy monitoring once they have been taking the medication for 5 years. Patients who have additional risk factors, should be referred for retinopathy monitoring once they have been taking the medication for 1 year.' Additional risk factors are exceeding the recommended daily dose, concomitant tamoxifen use, and eGFR less than 60 ml/min/1.73m2
  • US label: baseline retinal exam and exams during treatment are recommended — irreversible retinal damage is related to cumulative dosage and treatment duration
  • Discontinue immediately on any pigmentary abnormality, visual field defect, or other abnormality not explainable by difficulty in accommodation or corneal opacities, and advise patients to stop and seek advice for any visual disturbance including abnormal colour vision (UK SPC §4.4)
  • Clinical monitoring for signs and symptoms of cardiomyopathy, discontinuing if it develops; ECG considerations where other QT-prolonging or arrhythmogenic drugs are unavoidable (UK SPC §4.4, US §5.1 and §7.1)
  • US label: discontinue if myelosuppression occurs (haematologic toxicity), and discontinue if renal toxicity is suspected or demonstrated by tissue biopsy in any organ system
  • Blood glucose in patients on insulin or antidiabetic drugs — hydroxychloroquine can enhance their effect and cause hypoglycaemia (US §7.2)
  • Estimate plasma hydroxychloroquine levels in patients with severely compromised renal or hepatic function and adjust the dosage accordingly (UK SPC §4.4)
  • Be alert to hepatitis B reactivation, reported with hydroxychloroquine in combination with other immunosuppressants (UK SPC §4.4)
  • Prophylaxis adherence: the weekly dose must be started 2 weeks before travel, taken on the same day each week, and continued for 4 weeks after leaving the endemic area (US §2.2)

Clinical monograph

How it works

It accumulates in lysosomes and raises intracellular pH, interfering with antigen processing and immune signalling; this immunomodulatory effect underlies its use in autoimmune disease.

Prescribing in practice

  • Long-term use carries a risk of irreversible retinal toxicity — baseline and ongoing annual retinal monitoring is recommended (Royal College of Ophthalmologists), with dose related to body weight.
  • It can prolong the QT interval and has a very long half-life, so effects and interactions persist after stopping.
  • It is generally continued during pregnancy in SLE, where the benefits of disease control are considered to outweigh the risks.

Monitoring

Arrange baseline retinal assessment and annual screening after a defined period of treatment per Royal College of Ophthalmologists guidance, dose according to body weight, and review renal and hepatic function and QT risk where relevant.

Counselling the patient

  • Attend your eye-screening appointments and report any change in vision, such as difficulty reading, missing areas or altered colour vision.
  • Take it as prescribed; the benefit in joint or lupus disease builds gradually over weeks to months.
  • Do not stop it in pregnancy without advice, as continuing usually protects against lupus flares.

Evidence & guidelines

A cornerstone DMARD in SLE that reduces flares and is associated with better outcomes, and an established treatment in rheumatoid arthritis; supported by UK rheumatology and ophthalmology guidance.

Reference: PHE Malaria Prevention Guidelines 2023; BSR Hydroxychloroquine Retinopathy Guidelines; MHRA SPC Plaquenil; RECOVERY Trial 2020; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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