Drug Monograph
Hydroxychloroquine
Plaquenil
Pharmacokinetic Profile
Half-Life
40–50 days (terminal)
Metabolism
Hepatic (CYP2C8, CYP3A4, CYP2D6) to active desethyl metabolite
Protein Binding
~50%
Bioavailability
Variable (30–100%); mean ~70%
Volume of Distribution
Very large (extensive tissue uptake)
Clinical Information
Drug Class
4-Aminoquinoline antimalarial / DMARD
Available Doses
Tablets: 200 mg (= 155 mg base)
Route
Oral
Renal Adjustment
Use with caution; increased retinal toxicity risk
Hepatic Adjustment
Use with caution; hepatically metabolized
Pregnancy
Compatible — recommended to continue in SLE
Lactation
Compatible — low levels in breast milk
Schedule / Legal Status
Prescription only (not scheduled)
Generic Available
Yes
Indications for Hydroxychloroquine
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Rheumatoid arthritis | Adults | Monotherapy or combination DMARD | FDA Approved |
| Systemic lupus erythematosus (SLE) | Adults | Background therapy (recommended for all SLE patients) | FDA Approved |
| Chronic discoid lupus erythematosus | Adults | Monotherapy | FDA Approved |
| Malaria — uncomplicated treatment | Adults & pediatric | Acute treatment (chloroquine-sensitive strains) | FDA Approved |
| Malaria — prophylaxis | Adults & pediatric | Weekly prophylaxis (chloroquine-sensitive areas only) | FDA Approved |
Hydroxychloroquine occupies a unique position in rheumatology as the safest conventional DMARD with the broadest immunomodulatory benefits. In SLE, hydroxychloroquine is considered a cornerstone therapy by the EULAR 2023 guidelines and is recommended for all patients unless contraindicated, as it reduces flares, organ damage accrual, thrombotic risk, and overall mortality. In RA, it is commonly used in combination DMARD strategies — particularly in triple therapy with methotrexate and sulfasalazine. For malaria, its use is limited to chloroquine-sensitive areas; clinicians should consult the CDC malaria website before prescribing.
Off-Label Uses
Sjogren syndrome — for fatigue, arthralgias, and sicca symptoms (evidence quality: Moderate).
Antiphospholipid syndrome — adjunctive thromboprophylaxis in primary and obstetric APS (EULAR, evidence quality: Moderate).
Dermatomyositis — cutaneous manifestations refractory to sun protection (evidence quality: Low).
Porphyria cutanea tarda — low-dose phlebotomy alternative (100 mg twice weekly); note hepatotoxicity risk (evidence quality: Moderate).
Sarcoidosis — skin and joint involvement (evidence quality: Low).
Dosing for Hydroxychloroquine
Adult — Autoimmune Indications
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| RA — initial DMARD therapy | 400–600 mg daily (single dose or divided BID) | 200–400 mg daily | ≤5 mg/kg actual body weight/day | Higher initial doses may shorten time to response; reduce once maintenance achieved Taper corticosteroids and NSAIDs as response develops |
| RA — triple DMARD combination (with MTX + SSZ) | 200–400 mg daily | 200–400 mg daily | ≤5 mg/kg/day | Used as part of step-up or parallel strategy ACR 2021 conditionally recommends triple therapy over MTX alone for moderate-high activity |
| SLE — background therapy (all patients) | 200–400 mg daily | 200–400 mg daily | ≤5 mg/kg/day | Continue indefinitely; reduces flares, organ damage, and mortality EULAR 2023 recommends HCQ for all SLE patients unless contraindicated |
| Discoid lupus erythematosus | 200–400 mg daily | 200–400 mg daily | ≤5 mg/kg/day | Response may take weeks to months Combine with sun protection and topical therapies |
Malaria
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Malaria prophylaxis — chloroquine-sensitive area | 400 mg PO once weekly | 400 mg weekly (same day each week) | 400 mg/week | Begin 1–2 weeks before travel; continue 4 weeks after leaving endemic area Pediatric: 5 mg/kg base weekly (max 310 mg base) |
| Malaria — acute treatment (uncomplicated) | 800 mg (620 mg base) initially | 400 mg (310 mg base) at 6, 24, and 48 hours | Total: 2 g over 48 hours | Not for complicated malaria or chloroquine-resistant areas Pediatric: total 25 mg base/kg over 48 h (10 mg/kg initial, then 5 mg/kg at 6, 24, 48 h) |
Clinical Pearl: Weight-Based Dosing Protects the Retina
The most critical dosing rule for long-term hydroxychloroquine use is weight-based: daily doses should not exceed 5 mg/kg of actual body weight (AAO 2016). A 60 kg patient should receive no more than 300 mg/day (i.e., 200 mg daily, not 400 mg). Prescribing the standard 400 mg/day dose to patients of small stature is the single most common correctable risk factor for retinal toxicity. Always calculate the weight-based maximum before writing the prescription.
Pharmacology of Hydroxychloroquine
Mechanism of Action
The precise immunomodulatory mechanism of hydroxychloroquine remains incompletely understood. As a weak base, it accumulates in lysosomes and raises intracellular pH, which disrupts antigen processing and peptide-MHC class II complex formation — thereby reducing T-cell activation. It also inhibits Toll-like receptor (TLR) 7 and 9 signalling by preventing endosomal acidification, which suppresses the production of type I interferons and pro-inflammatory cytokines including IL-1, IL-6, IL-17, TNF-alpha, and interferon-alpha and gamma. Beyond immunomodulation, hydroxychloroquine has antiplatelet and antithrombotic effects relevant to antiphospholipid syndrome, improves lipid and glucose metabolism, and may provide cardiovascular protection in SLE patients. Its antimalarial activity relies on accumulation within the Plasmodium digestive vacuole, where it inhibits haem polymerization and produces toxic free haem.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Variable bioavailability 30–100% (mean ~70%); Tmax ~3–4 h; food does not significantly affect extent of absorption | Large inter-patient variability explains differences in clinical response at equivalent doses; blood level monitoring can aid adherence assessment in SLE |
| Distribution | Very large Vd (extensive tissue uptake); ~50% plasma protein-bound; concentrates in liver, spleen, kidney, lung, melanin-containing tissues (retina, skin) | Affinity for melanin explains retinal and dermatologic toxicity; very long washout time; tissue levels persist months after discontinuation |
| Metabolism | Hepatic via CYP2C8, CYP3A4, CYP2D6; primary metabolite: desethylhydroxychloroquine (active); also desethylchloroquine and bisdesethylchloroquine | CYP inhibitors/inducers may alter blood levels; metabolic pathway knowledge is relevant for interaction prediction |
| Elimination | Terminal t½ ~40–50 days; renal clearance accounts for ~15–25% of total; steady state reached at approximately 6 months | Extremely long half-life means therapeutic and toxic effects persist long after stopping; retinopathy can progress for months after discontinuation; loading doses are unnecessary for chronic use |
Side Effects of Hydroxychloroquine
Hydroxychloroquine has an excellent long-term safety profile compared with other DMARDs and immunosuppressants. The following incidence data are derived from the FDA prescribing information, randomized controlled trials, and long-term cohort studies.
≥10%
Very Common
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Nausea and stomach upset | 10–25% | Most common reason for early discontinuation; improves substantially when taken with food or milk; typically resolves within 1–2 weeks of initiation |
| Diarrhea and abdominal pain | 7–23% | Dose-related; the lower end of the range reflects standard chronic dosing, the higher end reflects acute loading doses used in trials |
1–10%
Common
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Headache | ~5% | Usually self-limiting; more common in first weeks of therapy |
| Skin rash and pruritus | 1–5% | May necessitate discontinuation; distinguish from disease-related rash in SLE patients |
| Blurred vision and accommodation difficulty | 1–10% | Dose-related and reversible on cessation; due to ciliary body effects, NOT retinal toxicity; do not confuse with the irreversible retinal changes that require screening |
| Dizziness and lightheadedness | ~5–7% | Usually transient; slightly above placebo rates in RCT data |
Serious
Serious (Regardless of Frequency)
| Adverse Effect | Estimated Frequency | Typical Onset | Required Action |
|---|---|---|---|
| Retinal toxicity (bull’s eye maculopathy) | <1% at 5 years; ~7.5% after 5+ years; up to 20% after 20 years | Usually after ≥5 years of use; risk rises sharply with cumulative dose | Irreversible — early detection through screening is essential. Discontinue immediately if toxicity detected on SD-OCT or visual field testing. Can progress for months after stopping due to long tissue half-life |
| Cardiomyopathy (including cardiac failure) | Rare (0.01–0.1%) | Usually after prolonged use (years) | Discontinue HCQ; echocardiography and cardiology referral; may be reversible with early drug cessation |
| QT prolongation / ventricular arrhythmias / torsades de pointes | Rare | Any time; higher risk with QT-prolonging co-medications, electrolyte disturbances, cardiac disease | Avoid co-administration with other QT-prolonging drugs; correct hypokalemia and hypomagnesemia; consider baseline ECG in patients with cardiac risk factors |
| Hypoglycaemia (including loss of consciousness) | Uncommon | Any time; risk higher in patients on antidiabetic medications | Warn patients about hypoglycaemia symptoms; may require adjustment of antidiabetic medications when starting or stopping HCQ |
| Neuromyopathy (proximal muscle weakness, absent deep tendon reflexes) | Rare | Usually after prolonged therapy; may mimic disease-related myopathy in SLE | Discontinue HCQ; EMG/NCS; usually reversible after stopping but recovery may be slow |
| Neuropsychiatric reactions including suicidality | Rare (FDA label updated 2023) | Variable | Monitor for mood changes, psychosis, suicidal ideation; discontinue if suspected and perform psychiatric assessment |
| Severe dermatologic reactions (SJS, TEN, DRESS, AGEP) | Very rare (<0.01%) | Days to weeks after initiation | Immediate discontinuation; emergency dermatologic and supportive care |
| Blood dyscrasias (agranulocytosis, aplastic anaemia, thrombocytopenia) | Very rare | Variable | CBC monitoring; discontinue if significant cytopenias develop |
Discontinuation
Discontinuation Rates
Short-term discontinuation (first year)
~10–15%
Top reasons: GI intolerance (nausea, diarrhea), skin rash, headache
Long-term discontinuation
Primarily retinal toxicity concern
Key factor: Retinal toxicity detected on screening prompts permanent discontinuation, especially after >5 years of use
| Reason for Discontinuation | Incidence | Context |
|---|---|---|
| GI intolerance | Most common early reason | Often manageable with food; typically first 2–4 weeks |
| Retinal toxicity | Primary long-term reason | Requires permanent discontinuation; cannot rechallenge |
| Dermatologic reactions | Uncommon | Rash may be drug-related or disease-related in lupus |
Managing Retinal Toxicity Risk — The Defining Long-Term Concern
Retinal toxicity is the most important safety consideration for long-term hydroxychloroquine use. It is irreversible once established and can progress even after discontinuation due to the drug’s extremely long tissue half-life. The key to prevention is weight-based dosing (≤5 mg/kg/day of actual body weight) and adherence to AAO screening recommendations: baseline exam within the first year, then annual screening starting after 5 years of use (or sooner if risk factors are present). SD-OCT and automated visual fields (10-2) are the preferred screening modalities. In patients of Asian descent, pericentral retinopathy is more common, so wider-field visual field testing (24-2 or 30-2) should be included.
Drug Interactions with Hydroxychloroquine
Hydroxychloroquine is metabolized by CYP2C8, CYP3A4, and CYP2D6 and is an inhibitor of CYP2D6, OAT1, OAT3, OCT1, and OCT2. Its most clinically significant interactions involve QT prolongation risk and pharmacokinetic effects on digoxin and antidiabetic agents.
Major
QT-Prolonging Drugs (azithromycin, fluoroquinolones, antiarrhythmics, antipsychotics)
MechanismAdditive QT prolongation via cardiac ion channel blockade
EffectIncreased risk of torsades de pointes, ventricular arrhythmias, and sudden death
ManagementAvoid combination if possible; if unavoidable, monitor ECG and correct electrolytes; consider baseline and on-treatment QTc measurement
FDA PI
Major
Tamoxifen
MechanismBoth drugs accumulate in melanin-containing tissues including the retina
EffectSynergistic increase in retinal toxicity risk; tamoxifen independently causes retinal crystal deposits
ManagementClassify as high-risk for retinopathy; earlier and more frequent ophthalmologic screening (annual from initiation)
AAO 2016 Guidelines
Moderate
Digoxin
MechanismHydroxychloroquine increases serum digoxin concentrations via unknown mechanism (possibly reduced clearance)
EffectRisk of digoxin toxicity (nausea, arrhythmias, visual disturbances)
ManagementMonitor serum digoxin levels closely when initiating, adjusting, or discontinuing HCQ
FDA PI
Moderate
Insulin and Oral Hypoglycaemics
MechanismHCQ enhances insulin sensitivity and reduces insulin clearance
EffectLife-threatening hypoglycaemia, including loss of consciousness, has been reported
ManagementWarn patients; may need to reduce antidiabetic doses when starting HCQ; monitor blood glucose more frequently during initiation and titration
FDA PI
Moderate
Mefloquine and Other Seizure Threshold-Lowering Agents
MechanismBoth agents lower the seizure threshold
EffectIncreased seizure risk
ManagementAvoid combination; use alternative antimalarial prophylaxis if HCQ is being used for autoimmune indications
FDA PI
Moderate
CYP2D6 Substrates (metoprolol, tamoxifen, codeine)
MechanismHCQ inhibits CYP2D6, reducing metabolism of substrates
EffectIncreased plasma levels of CYP2D6 substrates; reduced activation of prodrugs (codeine, tamoxifen)
ManagementMonitor for adverse effects of substrate drugs; consider dose adjustment or alternatives
FDA PI
Minor
Antacids and Kaolin
MechanismReduced GI absorption of HCQ via chelation or adsorption
EffectPotentially reduced HCQ efficacy
ManagementSeparate administration by at least 4 hours
FDA PI
Minor
Praziquantel
MechanismChloroquine reduces praziquantel bioavailability; same interaction cannot be ruled out with HCQ
EffectPotentially reduced praziquantel efficacy
ManagementSpace administration or use alternative anthelmintic if possible
FDA PIMonitoring for Hydroxychloroquine
-
Ophthalmologic exam (SD-OCT + 10-2 VF)
Baseline within first year; annual screening after 5 years of use
Routine AAO 2016 guideline. Begin annual screening earlier if risk factors present: dose >5 mg/kg/day, renal impairment, tamoxifen use, or pre-existing macular disease. In Asian patients, include 24-2 or 30-2 visual fields to detect pericentral toxicity pattern. SD-OCT and automated visual fields are the primary screening tools; multifocal ERG is supplementary -
CBC with differential
Baseline, then periodically
Routine Screen for rare blood dyscrasias including leukopenia, thrombocytopenia, and aplastic anaemia; frequency at prescriber discretion, typically every 6–12 months -
Blood glucose
At initiation and periodically in diabetic patients
Trigger-based HCQ can cause severe hypoglycaemia; monitor closely when starting HCQ in patients on insulin or sulfonylureas; may need to reduce antidiabetic medication doses -
Muscle strength and deep tendon reflexes
Periodically on long-term therapy
Routine Screen for neuromyopathy, which can mimic disease-related weakness in SLE; if proximal weakness develops, obtain CK and consider EMG/NCS -
ECG
Baseline in patients with cardiac risk factors
Trigger-based HCQ prolongs QT interval; baseline ECG recommended for patients with pre-existing cardiac disease, electrolyte abnormalities, or concurrent QT-prolonging medications -
HCQ blood levels
Periodically in SLE
Trigger-based Whole blood HCQ levels can assess adherence and may predict retinopathy risk; target levels >500 ng/mL in SLE may correlate with reduced flare risk; useful for suspected non-adherence
Contraindications & Cautions for Hydroxychloroquine
Absolute Contraindications
- Known hypersensitivity to hydroxychloroquine or any 4-aminoquinoline compound
- Pre-existing retinal or macular disease where reliable screening is not possible and alternative therapy exists
Relative Contraindications (Specialist Input Recommended)
- Porphyria — HCQ can exacerbate porphyria; avoid in patients with known porphyria. Cases of severe hepatotoxicity (transaminases >20× ULN) have been reported in porphyria cutanea tarda patients
- Pre-existing cardiomyopathy or conduction disorders — HCQ can cause cardiomyopathy and prolonged QT; use with close cardiac monitoring
- G6PD deficiency — theoretical risk of haemolysis, though clinically significant haemolysis is rare with HCQ (more common with chloroquine and primaquine)
- Psoriasis — HCQ may precipitate or exacerbate psoriasis attacks
- Epilepsy — HCQ may lower the seizure threshold
Use with Caution
- Renal impairment — reduced drug clearance increases retinal and systemic toxicity risk; dose adjustment and earlier retinal screening recommended
- Hepatic impairment — hepatically metabolized; may accumulate
- Elderly patients — age-related renal decline and concurrent medications increase toxicity risk; assess macular status carefully as age-related changes can complicate screening
- Children <31 kg — Plaquenil tablets not recommended due to inability to dose appropriately; alternative formulation needed
FDA Class-Wide Regulatory Warning
Retinal Toxicity and Cardiac Effects
Irreversible retinal damage has been observed in patients receiving long-term or high-dose 4-aminoquinoline therapy. Retinopathy may progress even after drug discontinuation. QT prolongation, ventricular arrhythmias (including torsades de pointes), and cardiac failure have been reported. HCQ should not be used with other QT-prolonging drugs. Neuropsychiatric reactions including suicidality have been reported (label update 2023). Severe hypoglycaemia, including loss of consciousness, can occur.
Patient Counselling for Hydroxychloroquine
Purpose of Therapy
Explain that hydroxychloroquine modulates the immune system gently rather than suppressing it heavily. In lupus, it is the only medication proven to reduce organ damage and improve survival when taken long-term, which is why it is recommended for all lupus patients. In RA, it helps control joint inflammation as part of a combination approach. The drug works slowly — patients should expect 2 to 6 months before noticing the full benefit — and it is important to continue taking it even when feeling well.
How to Take
Take hydroxychloroquine with food or milk to minimise stomach upset. Swallow the tablet whole — do not crush, chew, or split. It is typically taken once or twice daily at the same time each day. If using antacids, separate them from hydroxychloroquine by at least 4 hours.
Eye Health and Regular Screening
Tell patient
Long-term use of hydroxychloroquine can rarely affect the retina at the back of the eye. This is detectable with specialised tests long before any vision changes occur. You will need a baseline eye exam within the first year and then regular annual screening, typically starting after 5 years. If detected early and the drug is stopped, severe vision loss can be prevented.
Call prescriber
If you notice any change in vision, difficulty reading, missing spots in your visual field, or increased sensitivity to light — even if your scheduled eye exam is not due yet.
Stomach Upset
Tell patient
Nausea and diarrhea are the most common side effects but usually improve within the first 1–2 weeks. Taking the tablet with food or milk significantly reduces stomach symptoms. If taking two tablets daily, splitting them to morning and evening may help.
Call prescriber
If nausea or diarrhea is severe or persists beyond 2 weeks despite taking with food.
Low Blood Sugar
Tell patient
Hydroxychloroquine can lower blood sugar, especially if you have diabetes or take diabetes medications. Be aware of symptoms including shakiness, sweating, rapid heartbeat, confusion, and dizziness.
Call prescriber
If you experience recurrent episodes of low blood sugar or loss of consciousness.
Pregnancy and Breastfeeding
Tell patient
Unlike most rheumatic disease drugs, hydroxychloroquine is considered safe during pregnancy and breastfeeding. In fact, for lupus patients, stopping hydroxychloroquine during pregnancy increases the risk of disease flares. Continue taking it unless specifically told otherwise by your specialist.
Call prescriber
If you become pregnant or plan pregnancy — to confirm that your current dose and monitoring plan remain appropriate.
Sun Sensitivity
Tell patient
Some patients notice increased sun sensitivity while taking hydroxychloroquine. This is especially relevant for lupus patients, whose disease is also triggered by UV exposure. Use broad-spectrum sunscreen (SPF 30+), protective clothing, and avoid prolonged sun exposure.
Call prescriber
If you develop a new or worsening rash, particularly after sun exposure.
Mood Changes
Tell patient
Rarely, hydroxychloroquine may cause mood changes, anxiety, unusual behaviour, or thoughts of self-harm. This risk was highlighted in a 2023 FDA label update.
Call prescriber
Immediately if you experience new or worsening depression, anxiety, agitation, hallucinations, or thoughts of harming yourself.
Sources
Regulatory (PI / SmPC)
- Plaquenil (hydroxychloroquine sulfate) — Full Prescribing Information. Advanz Pharma (US) Corp. Revised December 2024. DailyMed Primary regulatory source for all approved indications, dosing, adverse reactions, warnings (including 2023 updates for neuropsychiatric effects and porphyria), and drug interactions.
- Plaquenil (hydroxychloroquine sulfate) — FDA Label 2023 revision. FDA Label PDF Contains the 2023 label updates adding neuropsychiatric reactions including suicidality and porphyria-related hepatotoxicity warnings.
Key Clinical Trials & Systematic Reviews
- Melles RB, Marmor MF. The risk of toxic retinopathy in patients on long-term hydroxychloroquine therapy. JAMA Ophthalmol. 2014;132(12):1453-1460. DOI Landmark Kaiser Permanente retrospective study of 2,361 patients establishing modern retinal toxicity prevalence estimates: <1% at 5 years, ~7.5% after 5 years, up to 20% after 20 years.
- Petri M, Elkhalifa M, Li J, et al. Hydroxychloroquine blood levels predict hydroxychloroquine retinopathy. Arthritis Rheumatol. 2020;72(3):448-453. DOI Prospective Hopkins Lupus Cohort study demonstrating higher HCQ blood levels predict subsequent retinopathy risk; supports therapeutic drug monitoring.
- Barnard RA, Engel AS, Engel KA, et al. Safety of hydroxychloroquine among outpatient clinical trial participants for COVID-19. Open Forum Infect Dis. 2020;7(11):ofaa500. DOI Placebo-controlled RCT safety data providing modern adverse event rates: GI effects in 40% HCQ vs 18% placebo; no significant cardiac arrhythmia signal.
- Ruiz-Irastorza G, Ramos-Casals M, Brito-Zeron P, Khamashta MA. Clinical efficacy and side effects of antimalarials in systemic lupus erythematosus: a systematic review. Ann Rheum Dis. 2010;69(1):20-28. DOI Systematic review establishing HCQ’s disease-modifying benefits in SLE including reduction in flares, organ damage, and mortality.
Guidelines
- Marmor MF, Kellner U, Lai TYY, et al. Recommendations on screening for chloroquine and hydroxychloroquine retinopathy (2016 revision). Ophthalmology. 2016;123(6):1386-1394. DOI Current AAO guideline for retinal screening: baseline exam, annual screening after 5 years, weight-based dosing ≤5 mg/kg actual body weight, with expanded guidance for Asian patients.
- Fanouriakis A, Kostopoulou M, Andersen J, et al. EULAR recommendations for the management of systemic lupus erythematosus: 2023 update. Ann Rheum Dis. 2024;83(1):15-29. DOI Updated EULAR SLE management guidelines recommending HCQ for all patients unless contraindicated; targets blood levels to optimise efficacy.
- Fraenkel L, Bathon JM, England BR, et al. 2021 American College of Rheumatology guideline for the treatment of rheumatoid arthritis. Arthritis Care Res. 2021;73(7):924-939. DOI ACR RA guideline conditionally recommending triple DMARD therapy (MTX + SSZ + HCQ) as an alternative to biologic escalation for moderate-high disease activity.
Mechanistic / Basic Science
- Schrezenmeier E, Dorner T. Mechanisms of action of hydroxychloroquine and chloroquine: implications for rheumatology. Nat Rev Rheumatol. 2020;16(3):155-166. DOI Comprehensive review of HCQ immunomodulatory mechanisms including TLR inhibition, cytokine suppression, and metabolic effects relevant to SLE and RA.
- Yusuf IH, Charbel Issa P, Ahn SJ. Hydroxychloroquine-induced retinal toxicity. Front Pharmacol. 2023;14:1196783. DOI Comprehensive review of retinal toxicity pathophysiology, risk factors, screening approaches, and epidemiology including Asian descent pericentral pattern.
Pharmacokinetics / Special Populations
- Tett SE, Cutler DJ, Day RO, Brown KF. Bioavailability of hydroxychloroquine tablets in healthy volunteers. Br J Clin Pharmacol. 1989;27(6):771-779. DOI Key PK study establishing oral bioavailability, terminal half-life (40-50 days), and time to steady state (~6 months) in healthy volunteers.
- Fairley JL, Nikpour M, Mack HG, Brosnan M, Saracino AM, Pellegrini M, Wicks IP. How toxic is an old friend? A review of the safety of hydroxychloroquine in clinical practice. Intern Med J. 2023;53(3):311-317. DOI Recent comprehensive safety review covering GI, cardiac, ocular, neuropsychiatric, and metabolic adverse effects with frequency estimates for clinical practice.