M Toronto Myositis Centreat St. Michael's Hospital
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Hydroxychloroquine

Plaquenil · say “hy-drox-ee-KLOR-o-kwin”
Antimalarial / DMARD
iUsed in myositis based on specialist experience and evidence, not a formal Canadian myositis approval.
i
Annual eye exam required.

Regular eye screening is your key safeguard on this medication. It catches rare retinal changes early, long before they could affect your vision.

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What it is

One of the gentlest, safest long-term options.

Hydroxychloroquine was originally developed for malaria and is now widely used in rheumatology. It gently modulates the immune system, reducing the overactivity that causes inflammation in dermatomyositis, rheumatoid arthritis, Sjogren’s, and other autoimmune diseases. It is one of the safest long-term medications in the field, and it is particularly good for the skin features of dermatomyositis.

How to take it
  • Available as 200 mg tablets. Usual dose is 200 to 400 mg daily (one or two tablets), once or twice a day.
  • Take with food or milk to reduce the chance of stomach upset.
  • Your doctor calculates the safest dose from your actual body weight (maximum 5 mg/kg/day) to protect your eyes.
  • If you miss a dose, take it when you remember; if the next dose is near, skip it and never double up.
  • Store at room temperature, away from children.
What to expect
  • It takes 8 to 12 weeks to reach full effect, and up to 6 months for some people to notice the full benefit.
  • Do not stop because it seems slow; it is working gradually to calm your immune system.
  • You can stop it without tapering, but discuss it with your doctor first.
Benefits

How it helps you.

Controls disease activity

Reduces inflammation and immune overactivity in dermatomyositis and related conditions.

Prevents flares

Continuing it significantly reduces the frequency and severity of flares.

Improves skin

Particularly effective for dermatomyositis rashes, including heliotrope and Gottron’s papules.

Excellent safety profile

One of the safest long-term medications in rheumatology, well tolerated by most people.

Helps cholesterol and blood sugar

Favourable effects on lipids and glucose, a bonus for people on steroids.

Reduces clot risk

Shown to lower the risk of blood clots in autoimmune disease.

Risks & side effects

What you should know.

Your doctor prescribed this because the expected benefits outweigh the risks for your situation. Here is the honest, full picture.

Common side effects
Nausea or stomach upset
The most common effect, usually mild and often resolved by taking it with food.
Diarrhea
Can occur early and usually settles as your body adjusts.
Headache
Occasional and manageable with standard pain relief.
Sun sensitivity
Your skin may burn more easily. Wear SPF 30+ sunscreen, a hat, and protective clothing.
Serious but uncommon
Retinal toxicity
The most important long-term risk. Rarely, it can affect the retina. Risk is very low in the first 5 years (under 1%) and rises with duration and dose. Detected by annual eye exams.
Skin rash
Rarely, an allergic-type rash. Stop and contact your doctor if this develops.
Muscle weakness
Very rarely, long-term use can affect muscle. Report new progressive weakness.
Heart rhythm changes
Very rarely, and typically only at high doses or very long-term use. Report palpitations or fainting.
Staying safe

Monitoring and precautions.

Regular monitoring
  • Annual eye exam with a baseline in the first year, then screening (including OCT and visual fields) to catch retinal changes early.
  • Your dose is weight-based to keep it within the safe range.
  • Screening is more frequent if you take a higher dose, have kidney disease, are also on tamoxifen, or have existing eye disease.
Daily precautions
  • Keep your annual eye exam. It is the single most important thing you can do to stay safe on this medication.
  • Use SPF 30+ sunscreen, a hat, and protective clothing, since it can increase sun sensitivity.
  • It works well alongside other immune-suppressing medicines, and on its own has minimal immune suppression.
  • Take it with food or milk to reduce stomach upset.
When to call your doctor

Contact the clinic if you notice:

Vision changes
Blurred vision, trouble reading, blind spots, poor night vision, or faded colours. Report for an urgent eye exam.
New skin rash
Stop and call if you develop a new rash, since it can rarely cause skin reactions.
Ringing in the ears
New ringing, buzzing, or hearing change. A rare effect that usually resolves when the dose is adjusted.
Persistent nausea or diarrhea
Mild upset is common early, but persistent or severe symptoms should be reported.
New muscle weakness
New or progressive weakness in the arms or legs. Very rare, but report it for evaluation.
Palpitations or dizziness
Irregular heartbeat or fainting. Very rare, but report it, especially at high doses.

Pregnancy & breastfeeding

Hydroxychloroquine is safe to continue during pregnancy and breastfeeding. In fact, it is often recommended for dermatomyositis patients to reduce flare risk during pregnancy. Always tell your doctor if you are pregnant or planning.

!

This guide is for education, not medical advice. Myositis treatment is individual, and many of these medications are used based on specialist experience and research rather than a single approval for myositis. Never start, stop, or change a medication without your own doctor. Your doses and choices are decided with your care team at the Centre.

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