What is Hydroxychloroquine?
Hydroxychloroquine (brand name Plaquenil) is an antimalarial drug that has become one of the most important medications in rheumatology. Originally developed in the 1950s as a less toxic derivative of chloroquine, it is now widely used as a disease-modifying antirheumatic drug (DMARD) for autoimmune conditions. It belongs to the 4-aminoquinoline class of drugs and works by modulating the immune system rather than suppressing it entirely.
The mechanism of action of hydroxychloroquine is multifaceted and not completely understood. It accumulates in lysosomes, raising the intracellular pH and interfering with antigen processing and presentation. It also inhibits toll-like receptor signaling (particularly TLR7 and TLR9), reduces the production of pro-inflammatory cytokines (including TNF-alpha, IL-1, and IL-6), and has antithrombotic properties. In malaria, it concentrates in the parasite's food vacuole and prevents the detoxification of heme, which is toxic to the parasite.
Hydroxychloroquine is generally well-tolerated, making it suitable for long-term use. It has favorable effects on lipid profiles and glucose metabolism, and it may reduce cardiovascular risk in patients with autoimmune diseases. These additional benefits have contributed to its widespread adoption as a foundational therapy in lupus and rheumatoid arthritis management.
Indications
Rheumatoid Arthritis (RA)
Hydroxychloroquine is used as a first-line DMARD in mild to moderate rheumatoid arthritis, often in combination with methotrexate and sulfasalazine (triple therapy). It helps reduce joint inflammation, pain, and swelling. While it is the mildest DMARD, it is valued for its safety profile and its ability to improve outcomes when added to other DMARDs. It typically takes 2 to 6 months to achieve full therapeutic effect.
Systemic Lupus Erythematosus (SLE)
Hydroxychloroquine is considered a cornerstone of lupus treatment. Current guidelines recommend that virtually all patients with SLE be treated with hydroxychloroquine unless there is a specific contraindication. It reduces disease flares by 50%, decreases organ damage accrual, improves survival, and has beneficial effects on lipid profiles and thrombotic risk. It is effective for skin manifestations, joint symptoms, and constitutional symptoms such as fatigue.
Malaria Prophylaxis
Hydroxychloroquine is used for the prevention of malaria caused by Plasmodium vivax, P. ovale, P. malariae, and susceptible strains of P. falciparum. It is taken weekly, starting 2 weeks before entering a malaria-endemic area and continuing for 4 weeks after leaving. It is not effective against chloroquine-resistant P. falciparum, which is prevalent in many parts of Southeast Asia and sub-Saharan Africa.
Dosing Guidelines
The 2016 American Academy of Ophthalmology (AAO) guidelines revised the recommended maximum dose from 6.5 mg/kg of ideal body weight to 5 mg/kg of actual body weight. This change was based on evidence that retinopathy risk correlates better with actual body weight dosing and that the previous guideline led to overdosing in short or obese patients.
| Indication | Dosing | Notes |
|---|---|---|
| Rheumatoid Arthritis | ≤ 5 mg/kg/day (typically 200–400 mg/day) | Usually taken once or twice daily with food |
| Lupus (SLE) | ≤ 5 mg/kg/day (typically 200–400 mg/day) | Long-term therapy; rarely discontinued |
| Malaria Prophylaxis | 400 mg once weekly | Start 2 weeks before travel; continue 4 weeks after |
Hydroxychloroquine is available as 200 mg tablets (equivalent to 155 mg of hydroxychloroquine base). Doses are typically rounded to the nearest 200 mg since the tablets cannot be easily split. For patients whose calculated maximum dose falls between 200 and 400 mg, some clinicians alternate daily doses (e.g., 200 mg one day, 400 mg the next) to achieve an average that stays within the recommended limit.
Retinopathy Risk & AAO 2016 Guidelines
The most serious long-term side effect of hydroxychloroquine is retinal toxicity (hydroxychloroquine retinopathy), also known as bull's-eye maculopathy. The drug accumulates in the retinal pigment epithelium and can cause irreversible damage to photoreceptors, leading to permanent vision loss if not detected early.
The major risk factors for hydroxychloroquine retinopathy include:
- Daily dose > 5 mg/kg actual body weight: The single most important modifiable risk factor. Keeping the dose at or below 5 mg/kg/day substantially reduces risk.
- Duration of use > 5 years: Retinopathy is rare in the first 5 years of therapy but increases thereafter. After 10 years of use, the prevalence may exceed 10%.
- Renal impairment: Reduced clearance leads to higher drug levels and increased retinal exposure.
- Concurrent tamoxifen use: Approximately doubles the risk of retinopathy through unknown mechanisms.
- Pre-existing macular disease: May make the retina more susceptible to toxic damage.
Retinopathy Screening Protocol
The AAO 2016 guidelines recommend the following screening protocol for patients on long-term hydroxychloroquine therapy:
- Baseline examination: Within the first year of starting therapy. Includes a comprehensive eye exam, optical coherence tomography (OCT), and automated visual fields (10-2).
- Annual screening: Starting after 5 years of use (or sooner if additional risk factors are present). The primary screening tests are OCT and 10-2 visual fields.
- High-risk patients: Those with renal disease, high dose (>5 mg/kg/day), or concurrent tamoxifen use should begin annual screening sooner.
If early retinopathy is detected, discontinuation of hydroxychloroquine can prevent further progression, although existing damage is irreversible. This underscores the importance of regular screening and proper dosing.
Side Effects
Hydroxychloroquine is generally well-tolerated, but side effects can occur:
- Gastrointestinal: Nausea, vomiting, diarrhea, and abdominal cramps (most common; usually improve with food or dose reduction)
- Dermatologic: Skin rash, pruritus, hair thinning, and skin hyperpigmentation (blue-gray discoloration)
- Neuromuscular: Myopathy (rare), peripheral neuropathy
- Cardiac: Cardiomyopathy and conduction disorders (very rare, usually with long-term high-dose use)
- Ophthalmologic: Retinopathy (see above), corneal deposits (usually asymptomatic and reversible)
- Hematologic: Aplastic anemia, agranulocytosis, thrombocytopenia (all very rare)
- Hypoglycemia: Can lower blood sugar, which may be clinically significant in diabetic patients on hypoglycemic agents
Drug Interactions
Important drug interactions to be aware of include:
- Tamoxifen: Increases retinopathy risk; avoid combination if possible
- Digoxin: Hydroxychloroquine may increase digoxin levels; monitor digoxin concentration
- Insulin/Hypoglycemics: May enhance hypoglycemic effects; monitor blood glucose
- Cyclosporine: Hydroxychloroquine may increase cyclosporine levels
- QT-prolonging drugs: Theoretical risk of additive QT prolongation (amiodarone, azithromycin, etc.)
- Antacids: May reduce hydroxychloroquine absorption; separate doses by 4 hours
Special Populations
Pregnancy: Hydroxychloroquine is considered safe in pregnancy (FDA category N; extensive safety data in lupus pregnancies). Discontinuation in pregnant SLE patients is associated with increased flare risk and worse outcomes. Current guidelines recommend continuing hydroxychloroquine throughout pregnancy.
Breastfeeding: Small amounts are excreted in breast milk. It is generally considered compatible with breastfeeding based on available safety data.
Renal impairment: Dose reduction may be considered in patients with significant renal impairment (GFR < 30 mL/min), as the drug is partially renally excreted. Close ophthalmologic monitoring is essential.
Children: Hydroxychloroquine is used in pediatric lupus and juvenile idiopathic arthritis. Dosing is weight-based (≤5 mg/kg/day). The drug should be kept out of reach of children, as overdose can be rapidly fatal — as few as 3–4 tablets can be lethal in a toddler.
Frequently Asked Questions
Why was the dosing guideline changed from ideal body weight to actual body weight?
The 2016 AAO revision changed to actual body weight because studies showed that retinopathy risk correlates better with actual body weight dosing. Using ideal body weight led to underdosing in tall/overweight patients and overdosing in short patients. The 5 mg/kg of actual body weight threshold provides a more accurate safety limit for retinal toxicity prevention.
How long does it take for hydroxychloroquine to work?
Hydroxychloroquine has a slow onset of action. Patients typically begin to notice improvement in 6 to 12 weeks, with full therapeutic benefit occurring at 3 to 6 months. It is important to continue the medication for at least 6 months before concluding it is ineffective. In lupus, the benefits in terms of flare prevention and damage accrual are cumulative over years.
Can I take hydroxychloroquine with food?
Yes, and it is generally recommended to take hydroxychloroquine with food or a glass of milk to reduce gastrointestinal side effects. Food does not significantly affect the drug's absorption or efficacy.
What happens if I miss a dose?
Because hydroxychloroquine has a very long half-life (approximately 40 to 50 days), missing a single dose is unlikely to have a significant clinical impact. Take the missed dose as soon as you remember, unless it is close to the time of your next dose. Do not double up on doses.
Is hydroxychloroquine the same as chloroquine?
No. While both are 4-aminoquinoline antimalarial drugs, hydroxychloroquine is a less toxic derivative with a better safety profile. Hydroxychloroquine has a lower incidence of retinal toxicity and gastrointestinal side effects compared to chloroquine. The two drugs are not interchangeable, and dosing guidelines differ.