Hydroxychloroquine is a synthetic antimalarial agent derived from chloroquine. While it retains activity against Plasmodium species, it is more commonly used for autoimmune diseases due to its anti-inflammatory and immunomodulatory effects .
Indications
FDA-Approved Uses
- Malaria : Treatment and prophylaxis of Plasmodium vivax , P. ovale , P. malariae , and chloroquine-sensitive P. falciparum .
- Systemic Lupus Erythematosus (SLE) : Reduces skin lesions, fatigue, joint pain, and prevents disease flares.
- Rheumatoid Arthritis (RA) : DMARD used to control inflammation and prevent joint damage.
- Porphyria Cutanea Tarda
Off-Label Uses
- Juvenile Idiopathic Arthritis
- Primary Sjögren’s Syndrome
Hydroxychloroquine and COVID-19: Summary of Evidence
- Early in the COVID-19 pandemic, hydroxychloroquine was proposed as a potential treatment due to in vitro antiviral activity against SARS-CoV-2.
- Mechanism hypothesized:
- Interfered with endosomal pH needed for viral entry and replication.
- Inhibited binding of viral spike protein to ACE2 receptors.
- 2020 Recovery Trial (UK) and other RCTs found no clinical benefit.
- FDA revoked Emergency Use Authorization (EUA) in June 2020 due to lack of efficacy and risk of QT prolongation and cardiac arrhythmias.
Key Point: Hydroxychloroquine is not recommended for the prevention or treatment of COVID-19.
Mechanism of Action
Hydroxychloroquine has multiple mechanisms depending on the condition treated:
In Autoimmune Disorders:
- Increases lysosomal pH in antigen-presenting cells → impairs antigen processing and presentation.
- Inhibits toll-like receptors (TLR 7 and TLR 9) on plasmacytoid dendritic cells → ↓ interferon release.
- Reduces neutrophil chemotaxis and eosinophil activity.
- Suppresses autoantigen presentation , dampening immune activation.
In Malaria:
- Prevents the biocrystallization of heme into hemozoin in the parasite’s food vacuole.
- Accumulation of free heme is toxic to the parasite → lysis and death.
Pharmacokinetics
| Parameter | Details |
|---|---|
| Absorption | Rapid and complete GI absorption |
| Bioavailability | ~67–74% |
| Peak Plasma Time | 1–3 hours |
| Protein Binding | ~55% |
| Metabolism | Hepatic (CYP2D6, 2C8, 3A4/5) → N-desethylhydroxychloroquine |
| Excretion | Renal (partially unchanged); long half-life (40–50 days) |
Pharmacodynamics
- Lipophilic weak base → accumulates in lysosomes.
- Increases lysosomal pH → disrupts protein degradation and immune signaling.
- Alters MHC class II antigen processing.
- Inhibits intracellular pathways related to immune activation.
Onset and Duration
- Onset of Action : Typically 4–6 weeks; may take up to 6 months for full effect in autoimmune diseases.
- Duration of Action : Prolonged due to tissue accumulation (esp. skin, retina).
Therapeutic Benefits in Autoimmune Diseases
Hydroxychloroquine is considered first-line therapy in SLE due to:
- Antithrombotic properties : Decreases lupus-associated thrombosis.
- Glycemic control : Improves insulin sensitivity.
- Lipid profile improvement : ↓ LDL and triglycerides.
- ↓ Disease flares and long-term organ damage.
Adverse Effects
| System | Adverse Effect |
|---|---|
| Ocular | Retinopathy (dose-dependent; screen annually) |
| Cardiac | QT prolongation, cardiomyopathy (rare but serious) |
| GI | Nausea, diarrhea, abdominal pain |
| Dermatologic | Hyperpigmentation, rash |
| Hematologic | Bone marrow suppression (rare) |
| CNS | Headache, dizziness |
Retinopathy risk increases with daily doses >5 mg/kg of actual body weight and long-term use (>5 years).
Contraindications
- Hypersensitivity to 4-aminoquinoline compounds
- Retinal or visual field changes
- Pre-existing maculopathy
Monitoring Parameters
- Ophthalmologic exam : Baseline + annually after 5 years of use (or earlier if risk factors)
- CBC and LFTs if long-term use
- Baseline ECG if other QT-prolonging drugs are used
