Hydroxychloroquine

Hydroxychloroquine is prescribed to treat:

• Lupus, rheumatoid arthritis, and malaria • Various related conditions in the immunology category • Associated symptoms and complications

It is an important medication that helps manage these conditions effectively.

Hydroxychloroquine (Plaquenil) is an antimalarial used as a disease-modifying agent in systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome. In lupus it is not merely one option among several — it is recommended for essentially all patients, long-term, because the benefits extend well beyond symptom control.

Mechanism of Action

Hydroxychloroquine accumulates in acidic intracellular compartments, particularly lysosomes, and raises their pH. That single physical effect has several immunologic consequences: impaired antigen processing and presentation, and — most importantly — inhibition of Toll-like receptors 7 and 9, which normally detect nucleic acids.

TLR7 and TLR9 activation by self nucleic acids is a central driver of the interferon signature that characterises lupus. Blocking that pathway addresses a mechanism close to the root of the disease rather than its downstream inflammation, which is why hydroxychloroquine modifies the illness rather than only relieving it.

The benefits in lupus are broad and well established: fewer flares, reduced organ damage accrual over time, lower thrombosis risk, favourable effects on lipids and glucose, and improved survival. Few drugs in rheumatology have that range of demonstrated benefit, and it is the reason patients are kept on it even during quiescent disease.

Onset is slow. Hydroxychloroquine accumulates over months, and full effect may take three to six months. Patients expecting rapid relief conclude it is not working and stop, which is the most common avoidable reason for treatment failure.

Clinical Use

In lupus, hydroxychloroquine is background therapy for nearly everyone, continued indefinitely including through pregnancy — where stopping it increases flare risk and where continuing reduces neonatal lupus and congenital heart block in anti-Ro positive mothers.

In rheumatoid arthritis it is a conventional DMARD, useful in mild disease and in combination regimens, though considerably less potent than methotrexate. It is also used in Sjögren's syndrome for fatigue and joint symptoms.

Dosing is weight-based and capped, and the cap exists specifically to limit retinal toxicity. Exceeding it in pursuit of better disease control is a poor trade, since the ocular risk is cumulative and the additional efficacy is marginal.

Hydroxychloroquine received a great deal of attention as a proposed COVID-19 treatment in 2020. Randomised trials subsequently showed no benefit for prevention or treatment, and it is not used for that indication. The episode caused genuine shortages for patients with lupus who depend on it. Our immunology team manages these regimens, and the Lupus Foundation of America provides patient-level background.

Retinal Monitoring

Retinal toxicity is the reason hydroxychloroquine requires ongoing ophthalmologic monitoring, and it is the one aspect of treatment patients must not let lapse.

The drug accumulates in retinal pigment epithelium and can cause a characteristic bull's-eye maculopathy. Risk is low in the first five years at appropriate weight-based dosing, then rises with cumulative exposure — becoming meaningful after roughly five to ten years and climbing thereafter.

Crucially, established retinopathy does not reverse on stopping and can continue to progress. The entire purpose of screening is therefore to detect subclinical change before vision is affected, at which point discontinuation prevents further damage. Waiting for visual symptoms defeats the point, since by then irreversible loss has occurred.

Current guidance is a baseline examination within the first year and annual screening after five years, sooner and more often with higher dose, kidney impairment, concurrent tamoxifen, or existing retinal disease. Screening uses optical coherence tomography and automated visual fields rather than a routine eye examination, which will not detect early change — a distinction worth stating to patients, who often assume their regular optometrist visit covers it.

Monitoring and Follow-Up

Beyond ophthalmology, periodic complete blood count and liver and kidney function are checked. Kidney impairment reduces clearance and raises retinal risk, so dosing may need adjustment as function declines.

Hydroxychloroquine is generally well tolerated. Gastrointestinal upset is the most common early complaint and often settles or responds to taking it with food. Skin hyperpigmentation and hair changes occur. Cardiomyopathy is rare but reported with very long-term use.

It prolongs the QT interval modestly, which matters in combination with other QT-prolonging drugs — a consideration that received far more attention during the COVID-19 episode than it warrants in routine rheumatologic use at standard doses.

Adherence is worth checking directly. Because the drug works slowly and patients often feel well on it, non-adherence is common and is a frequent reason for apparently unexplained flares. Blood level measurement is available in some settings and can distinguish non-response from non-adherence. The MedlinePlus hydroxychloroquine entry covers prescribing detail.

Special Populations

Hydroxychloroquine is one of the few rheumatologic drugs considered safe in pregnancy and is actively recommended to continue, since stopping precipitates flares that carry greater fetal risk than the drug does. It is compatible with breastfeeding.

In older adults, kidney function and cumulative dose both warrant attention. In G6PD deficiency, hemolysis is a theoretical concern, though it is rarely a problem at usual doses. Existing retinal or macular disease raises the threshold for use and the intensity of monitoring. Pre-existing cardiomyopathy or QT prolongation warrants caution.

When to Contact Your Doctor

Report any change in vision — difficulty reading, missing patches in the visual field, changes in colour perception, or light sensitivity — promptly, and do not wait for a scheduled appointment. Confirm that your eye screening is the specific retinal screening protocol rather than a routine eye test.

Report muscle weakness, unexplained fatigue, or breathlessness. Report a rash, particularly a blistering or peeling rash. Gastrointestinal upset is common early and worth raising before stopping, since it often resolves.

Do not stop hydroxychloroquine because you feel well — that is the drug working, and stopping is a common cause of flare. If you are pregnant or planning pregnancy, continue it and discuss rather than stopping.

To review your eye screening schedule, address side effects, or discuss disease control, contact us or schedule a visit.