Hydroxychloroquine (Plaquenil) is an antimalarial drug and disease-modifying antirheumatic drug (DMARD) used to treat systemic lupus erythematosus (SLE), rheumatoid arthritis, and to prevent and treat malaria. In autoimmune disease, it works by raising lysosomal pH in antigen-presenting cells, impairing the processing and presentation of self-antigens that drive inflammatory activity. It is slower-acting than corticosteroids but considered a cornerstone long-term therapy for lupus due to its favorable safety profile and proven reduction in lupus flares and mortality. Annual ophthalmologic screening is required to detect early retinopathy, the most serious long-term toxicity.
Hydroxychloroquine
Uses & FDA Indications
Hydroxychloroquine is FDA-approved for the suppressive treatment and prophylaxis of malaria caused by Plasmodium vivax, P. malariae, P. ovale, and susceptible strains of P. falciparum; treatment of acute attacks of malaria; treatment of systemic lupus erythematosus (SLE); and treatment of rheumatoid arthritis in patients who have not responded adequately to other DMARDs.
In lupus, hydroxychloroquine is often called the cornerstone of therapy. Long-term use has been shown to reduce lupus flare frequency, decrease organ damage accrual, lower the risk of thrombotic events, and improve overall survival. It is generally recommended for all patients with SLE who can tolerate it, regardless of disease severity.
Off-label uses include Sjogren's syndrome, cutaneous lupus and discoid lupus erythematosus, antiphospholipid syndrome (as adjunct therapy), dermatomyositis, and porphyria cutanea tarda. Its anti-inflammatory and immunomodulatory properties make it valuable across a range of autoimmune conditions.
How It Works
Hydroxychloroquine is a weak base that concentrates in acidic intracellular compartments, particularly lysosomes and endosomes. By raising the pH of these compartments, it interferes with multiple cellular processes that depend on lysosomal acidity.
In autoimmune disease, the primary relevant mechanism is impairment of antigen presentation. Antigen-presenting cells (dendritic cells, macrophages, B cells) take up antigens via endocytosis; lysosomal enzymes then cleave proteins into peptides that are loaded onto MHC class II molecules for presentation to T cells. By raising lysosomal pH, hydroxychloroquine blunts this antigen processing and presentation step, reducing the activation of autoreactive T and B lymphocytes that drive inflammatory autoimmune activity.
Hydroxychloroquine also inhibits Toll-like receptors (TLRs), particularly TLR7 and TLR9, which reside in endosomal compartments and recognize nucleic acid antigens. In lupus, self-derived nucleic acids from apoptotic cells can inappropriately activate these TLRs, driving type I interferon production and the characteristic lupus inflammatory signature. By impairing TLR-endosomal signaling, hydroxychloroquine blunts this innate immune activation pathway — explaining much of its efficacy in lupus beyond simple antigen presentation modulation.
RETINOPATHY WARNING: Hydroxychloroquine can cause irreversible retinal damage (hydroxychloroquine retinopathy) with cumulative use. Risk is substantially higher in patients who have used the drug for more than 5 years, those with cumulative total doses above 1000 g, patients with renal impairment (which slows drug clearance), and those with pre-existing retinal or macular disease. Once established, hydroxychloroquine retinopathy may progress even after the drug is discontinued. Annual ophthalmologic screening with OCT and visual field testing is mandatory.
Side Effects
Common
- Gastrointestinal effects — nausea, abdominal discomfort, diarrhea; taking with food significantly reduces GI side effects
- Headache
- Skin and hair changes — pigmentation changes (blue-gray discoloration of skin, especially sun-exposed areas); bleaching of hair; these are dose-related and cosmetically concerning but not dangerous
- Pruritus — particularly in patients of African descent, due to differences in melanin-binding characteristics
Serious
- Retinopathy (bull's eye maculopathy) — the most serious long-term toxicity; irreversible vision loss in advanced cases; detected through annual screening
- Cardiomyopathy and cardiac conduction defects — rare, associated with long-term high cumulative doses; can cause cardiomyopathy, heart block, or ventricular arrhythmias
- QT prolongation — clinically important when combined with other QT-prolonging drugs
- Hemolytic anemia in G6PD deficiency — hydroxychloroquine can precipitate hemolytic anemia in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency; G6PD testing is recommended before initiation
- Neuromyopathy — rare; proximal muscle weakness and sensory symptoms
Drug Interactions
| Drug / Class | Interaction | Clinical Significance |
|---|---|---|
| QT-Prolonging Drugs (antipsychotics, fluoroquinolones, ondansetron, azithromycin) | Additive QT interval prolongation. Risk of torsades de pointes increases substantially when multiple QT-prolonging agents are combined. | High — review all concurrent medications for QT risk; obtain ECG at baseline and with new combinations |
| Digoxin | Hydroxychloroquine increases digoxin plasma concentrations, potentially to toxic levels. | High — monitor digoxin levels closely; digoxin dose reduction may be needed |
| Antidiabetic Drugs (insulin, sulfonylureas, metformin) | Hydroxychloroquine has intrinsic hypoglycemic effects (improves insulin sensitivity). Can potentiate blood glucose-lowering effects and increase hypoglycemia risk. | Moderate — monitor blood glucose more closely; antidiabetic drug dose adjustments may be needed |
| Antacids | May reduce absorption of hydroxychloroquine. Separate administration by at least 4 hours. | Low — timing adjustment recommended |
Warnings & Contraindications
Contraindications
- Known hypersensitivity to hydroxychloroquine, chloroquine, or 4-aminoquinolines
- Pre-existing maculopathy of any etiology
Retinal Monitoring Protocol
The American Academy of Ophthalmology (AAO) recommends baseline ophthalmologic examination within the first year of starting hydroxychloroquine, followed by annual screening after 5 years of use (or sooner in patients with risk factors such as renal impairment, high cumulative dose, or pre-existing macular disease). Preferred screening modalities include spectral-domain optical coherence tomography (SD-OCT) and visual field testing. Fundus photography and multifocal electroretinography provide additional sensitivity in high-risk patients.
G6PD Deficiency
Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency are at risk for drug-induced hemolytic anemia with hydroxychloroquine. G6PD screening before initiation is recommended, particularly in populations with higher G6PD deficiency prevalence (individuals of African, Mediterranean, and Southeast Asian descent).
Cardiac Monitoring
While cardiomyopathy and conduction defects are rare with hydroxychloroquine, a baseline ECG is advisable in patients with pre-existing cardiac conditions. Patients with unexplained worsening heart failure, new arrhythmias, or conduction abnormalities while on hydroxychloroquine should undergo cardiac evaluation including consideration of endomyocardial biopsy in select cases.
Check for QT prolongation and other interaction risks with hydroxychloroquine.
Check Drug Interactions →Frequently Asked Questions
Why does hydroxychloroquine require eye exams?
Hydroxychloroquine can accumulate in the retinal pigment epithelium over time, causing a pattern of damage called bull's eye maculopathy — a ring of retinal damage surrounding the fovea that in advanced stages leads to irreversible central vision loss. The risk increases substantially with cumulative total dose and duration of therapy, particularly after 5 years of use. Because early retinopathy can be detected by specialized testing before symptoms develop, and because discontinuing the drug early can halt or slow progression, the American Academy of Ophthalmology recommends baseline screening at treatment initiation and annual screening thereafter.
How long does hydroxychloroquine take to work for lupus?
Hydroxychloroquine has a slow onset of action when used for autoimmune conditions. Patients with lupus or rheumatoid arthritis typically notice initial benefits within 1–3 months, but the full anti-inflammatory and immunomodulatory effect may take 3–6 months to manifest. This slow onset is characteristic of disease-modifying antirheumatic drugs (DMARDs) generally and reflects the mechanism — gradual modulation of antigen presentation and inflammatory cytokine production rather than acute symptom suppression. Patients should not discontinue the drug prematurely due to perceived lack of effect.
Is hydroxychloroquine an immunosuppressant?
Hydroxychloroquine is immunomodulatory but not broadly immunosuppressive in the same sense as corticosteroids or biologics. It does not significantly increase the risk of opportunistic infections, does not require routine infection monitoring in the way that methotrexate or TNF inhibitors do, and does not require dose adjustment before most vaccinations. It is often considered one of the safer DMARDs in terms of infection risk, which is a meaningful advantage in patients with autoimmune conditions who are already at elevated baseline infection risk.