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# Hydroxychloroquine

An old antimalarial that is now a mainstay for lupus and rheumatoid arthritis. Long use needs regular eye checks because it can damage the retina.

Updated 2026-11-01

- Class: [Conventional disease-modifying antirheumatic drugs (DMARDs)](https://durgical.com/en/pharmacology/classes/conventional-disease-modifying-antirheumatic-drugs/)
- Target: Acidic intracellular vesicles (lysosomes; the malaria parasite's food vacuole)
- ATC code: P01BA02
- WHO Model List of Essential Medicines

## Mechanism of action

Hydroxychloroquine is a weak base that concentrates in acidic compartments. In the malaria parasite it accumulates in the acid vesicles and inhibits the polymerisation of haem, which is toxic to the parasite. In rheumatoid arthritis and lupus its anti-inflammatory and immunomodulatory mechanism is not fully known.

- As a weak base it is trapped in acidic vesicles
- Malaria: it blocks haem polymerisation in the parasite
- Autoimmunity: it dampens immune-cell signalling
- Disease activity falls slowly over months

## Pharmacokinetics

**Absorption**
Absorbed by mouth

**Distribution**
Very large volume of distribution; it concentrates in tissues

**Half-life**
Very long: terminal half-life of about 40 to 50 days

**Onset and duration**
In rheumatic disease, benefit takes weeks to months

## Indications

- Systemic lupus erythematosus and chronic discoid lupus [Systemic lupus erythematosus →](https://durgical.com/en/conditions/systemic-lupus-erythematosus/)
- Rheumatoid arthritis [Rheumatoid arthritis →](https://durgical.com/en/conditions/rheumatoid-arthritis/)
- Treatment and prophylaxis of uncomplicated malaria caused by chloroquine-sensitive parasites [Malaria →](https://durgical.com/en/conditions/malaria/)

## Adverse effects

### Common

- Nausea and vomiting
- Diarrhoea and abdominal pain
- Rash and itching
- Skin hyperpigmentation

### Serious (rare, important)

- Irreversible retinopathy, related to cumulative dose and duration
- Cardiomyopathy and ventricular arrhythmias, including QT prolongation and torsades de pointes
- Severe hypoglycaemia
- Haemolysis in G6PD deficiency
- Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis)
- Neuropsychiatric effects, including suicidality; myopathy

## Contraindications

- Hypersensitivity to 4-aminoquinolines

## Key interactions

**Drugs that prolong the QT interval**
Additive risk of ventricular arrhythmia.

**Insulin and other antidiabetic drugs**
Higher risk of hypoglycaemia.

**Digoxin**
Higher digoxin levels.

**Antacids and kaolin**
May reduce absorption; doses are spaced apart.

## What is monitored

- Baseline and regular retinal examination
- ECG in patients with heart disease or QT risk
- Blood glucose in people with diabetes
- Blood counts in long-term use

## Administration and safety

- Oral tablet, taken with food or milk.
- Do not crush or divide the tablets.
- Space antacids from the dose.

## Nursing care

- Make sure a baseline eye examination is arranged and regular checks are booked.
- Teach the patient to report blurred vision, trouble reading or seeing colours.
- Teach the signs of hypoglycaemia, especially in people with diabetes.
- Ask about palpitations, fainting or new breathlessness.
- Ask about other medicines that prolong the QT interval.

## Pregnancy and breastfeeding

Decades of use in pregnancy have not shown a clear rise in major birth defects; in lupus it is usually continued, as the treating team decides.

## Memory aid

Hydroxychloroquine: the Lupus Lamp that needs Long Looks at the retina.

## Test yourself

Think of the answer, then tap the question to see it.

## Which serious toxicity calls for regular eye examinations during hydroxychloroquine treatment?

Irreversible retinopathy, related to cumulative dose and duration of therapy.

## Why can hydroxychloroquine take months to show an effect in rheumatoid arthritis, while it acts faster in malaria?

In malaria it acts directly on the parasite; in autoimmune disease it slowly modulates immune signalling, and its very long half-life means steady tissue levels are reached only after weeks.

## Which metabolic adverse effect is a concern in a patient on insulin who starts hydroxychloroquine?

Hypoglycaemia, which can be severe; hydroxychloroquine can enhance the effect of insulin and other antidiabetic drugs.

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## Related drugs

- [Leflunomide](https://durgical.com/en/pharmacology/leflunomide/)

## Related conditions

- [Systemic lupus erythematosus](https://durgical.com/en/conditions/systemic-lupus-erythematosus/)
- [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/)
- [Malaria](https://durgical.com/en/conditions/malaria/)

[← Back to the class: Conventional disease-modifying antirheumatic drugs (DMARDs)](https://durgical.com/en/pharmacology/classes/conventional-disease-modifying-antirheumatic-drugs/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Hydroxychloroquine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a601240.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [DailyMed - HYDROXYCHLOROQUINE SULFATE tablet, film coated](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cf4b1912-9806-4ef3-bf17-152a96d75bbc) (DailyMed (U.S. National Library of Medicine), 2024); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=P01BA02) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/hydroxychloroquine/