Hydroxychloroquine

Medication antimalarial / DMARD other

Aka: Plaquenil

Brands seen in Singapore: Plaquenil, Haloxin, HCQS, Accoquin, Ovipla

Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.

How to use

What it’s for

Prescribed for lupus, rheumatoid arthritis and malaria

When to take

NHS: several weeks to work; often 6 months or longer

Take with

SG label: each dose with a meal or a glass of milk

Pros & cons

Pros

SG label: either 200 mg or 400 mg a day in adults
HealthHub: safe in pregnancy and breastfeeding
NHS: also used for sun-triggered skin conditions

Cons

NHS: stomach ache, nausea, headache, itchy rash
FDA: retinal damage tracks cumulative dose
FDA: qt prolongation and cardiomyopathy reported

Sources

HSA — Listing of Registered Therapeutic Products (open dataset on data.gov.sg; same register as HSA Infosearch) · read 2026-08-27
what it says
“Forensicclassification = 'Prescription Only' for all 6 hydroxychloroquine products on the register: SIN12213P PLAQUENIL TABLET 200 mg, SIN12669P and SIN11874P HALOXIN, SIN16632P HCQS, SIN16475P ACCOQUIN, SIN17243P OVIPLA — all oral tablets.”
MOH National Drug Formulary — PLAQUENIL TABLET 200 MG (White) [SIN12213P], SG product information (last updated 28 July 2026) · read 2026-08-27
what it says
“PRESCRIPTION ONLY MEDICINES … This dose should not exceed 6.5mg/kg/day (calculated from ideal body weight and not actual body weight) and will be either 200mg or 400mg per day … Each dose should be taken with a meal or glass of milk.”
HealthHub (MOH Singapore / Pharmaceutical Society of Singapore) — Hydroxychloroquine medication information leaflet (reviewed 14 Nov 2025) · read 2026-08-27
what it says
“a disease modifying anti-rheumatic drug (DMARD) … Take this medication with or after food … safe to be taken during pregnancy and when breastfeeding … Inform your doctor if you have G6PD deficiency.”
NHS Medicines A-Z — Hydroxychloroquine · read 2026-08-27
what it says
“It's only available with a prescription … swallow the tablets whole with a meal or glass of milk … It takes several weeks … it may not be suitable if you have liver, kidney, blood or heart problems, maculopathy.”
FDA / openFDA drug label — PLAQUENIL (hydroxychloroquine sulfate) tablets, prescribing information (effective 9 Apr 2026) · read 2026-08-27
what it says
“Daily doses exceeding 5 mg/kg (actual weight) of hydroxychloroquine sulfate increase the incidence of retinopathy … PLAQUENIL has a potential to prolong the QT interval … Avoid in patients with psoriasis … Avoid in patients with porphyria.”

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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.

In Singapore

Classification
HSA register

prescription-only

This is the Singapore classification, taken from the HSA register. Dosing stays with the label and your pharmacist or doctor — this page never tells you how much to take.

What the label says

The SG plaquenil label (sin12213p) sets the adult ceiling: 'This dose should not exceed 6.5mg/kg/day (calculated from ideal body weight and not actual body weight) and will be either 200mg or 400mg per day'; the US FDA plaquenil label instead warns that 'Daily doses exceeding 5 mg/kg (actual weight) of hydroxychloroquine sulfate increase the incidence of retinopathy' — the two ceilings differ in both number and weight basis; as directed on the label or by your doctor

Who should check first

Talk to a doctor or pharmacist before taking this if any of these apply to you.

Eye problems or maculopathy: NHS says it may not be suitable
G6pd deficiency: HealthHub says to
Psoriasis or porphyria: FDA label says avoid
Heart, liver, kidney or blood problems: NHS says

Documented interactions

With medicines and supplements

Drugs that prolong the qt interval or are arrhythmogenic: FDA: not recommended together — added risk of ventricular arrhythmias⁵
Digoxin: FDA: serum digoxin may rise; the label says monitor levels^5,4
Antacids and kaolin: FDA: absorption can drop; the label suggests a 4-hour gap · NHS lists indigestion medicines too^5,4
Insulin and other diabetes medicines: FDA: hypoglycaemia risk rises; a dose reduction may be needed⁵
Methotrexate: FDA: adverse reactions may be more frequent together⁵

Only combinations someone has written down appear here. A pair that is missing is unrecorded, not cleared.