Hydroxychloroquine and chloroquine
Hydroxychloroquine and chloroquine are anti-malarial medications. Besides being active against malaria, they are used to treat rheumatoid arthritis and cutaneous lupus erythematosus (LE) and rashes associated with systemic lupus erythematosus (SLE). They are also used in some photosensitivity disorders and occasionally in other inflammatory skin conditions. Hydroxychloroquine is used much more frequently than chloroquine, as chloroquine is more likely to cause permanent damage to eyesight.
Hydroxychloroquine is available in New Zealand as Plaquenil®, in 200 mg tablets. The usual dose for skin disease is 200 to 600 mg daily, best taken after meals.
Supply of chloroquine in New Zealand has been discontinued.
Drug interactions with antimalarials
Hydroxychloroquine may interfere with:
- Digoxin (increased digoxin concentrations)
- Monoamine oxidase inhibitors
- Insulin and other antidiabetic drugs
Chloroquine may interfere with:
- Antacids, kaolin (within 4 hours)
Contraindications to antimalarials
Antimalarial medications may be unsuitable in the following circumstances:
- Long term in young children (overdose is toxic); chloroquine may be more suitable than hydroxychloroquine in children
- Certain eye diseases i.e. pre-existing macular degeneration or retinopathy
- Allergy to 4-aminoquinoline compounds
- Severe gastrointestinal, neurological, heart or blood disorders
- Intermittent porphyria or variegate porphyria
- Glucose-6-phosphate dehydrogenase deficiency.
- Risk factors for QT prolongation (delayed heart ventricular response) including certain medications
Doses of hydroxychloroquine may need to be lower in those who have liver or kidney disease.
Hydroxychloroquine and chloroquine are classified as Category D in pregnancy. They should only be taken during pregnancy if essential.
Adverse effects of antimalarials
Adverse effects of antimalarials are uncommon. They include:
- Nausea and indigestion
- Dizziness, ringing in the ears, or decreased hearing
- Headache, seizures and peripheral neuropathy
- Muscle weakness (mainly thighs)
- Psychosis and other psychiatric disorders
- Visual disturbance including halos around lights, blurring of vision, corneal opacity (reversible on stopping treatment)
- Liver disease
- Heart disease
- Skin rashes (various types) including exacerbation of porphyria
- Itchy or darkened skin
- Hair loss or bleaching of hair
Antimalarials may aggravate psoriasis.
Antimalarials are highly toxic if taken in overdose, especially to the heart.
Visual effects of antimalarials
Visual toxicity due to antimalarials affects the retina. This may occur after chloroquine has been taken for a year or longer, or if the total dose is more than 1.6 g/kg bodyweight. Visual toxicity may also occur after hydroxychloroquine has been taken for several years (generally over 8 years continuous treatment). Unfortunately, decreased vision may be permanent. To decrease the chance of this occurring:
- Do not exceed a dose of 200 mg chloroquine or 400 mg hydroxychloroquine daily for more than a few weeks at a time.
- Wear sunglasses outdoors.
- Reduce the dose or stop the antimalarial if it is no longer required (with your doctor's permission) eg during the winter months.
- Check your vision with an Amsler grid (please note this is only a rough guide to detect visual field defects).
- Consult an ophthalmologist if you have visual symptoms (light flashes and streaks, decreased field of vision, night blindness or problems focusing), if you have been prescribed chloroquine, or after you have taken hydroxychloroquine for five years continuously (or an equivalent time for intermittent courses).
For patients taking hydroxychloroquine in New Zealand, most ophthalmologists recommend routine eye checks as a baseline if there is any visual impairment not corrected by glasses. Those without visual symptoms or visual impairment should be seen by an ophthalmologist for a full assessment after 5 years or so (earlier if there are symptoms). These checks are likely to include visual acuity, Ishihara colour test, examination of the back of the eye (fundus) and central visual field examination. Worrying features on examination include pigmentation (dark coloration) or loss of pigmentation of the retina, optic atrophy (damaged nerve) and scotoma (tunnel vision). An electroretinogram (ERG) may be performed if any screening tests are abnormal.
Place the grid on a flat surface and hold it at a distance of 33 cm. While looking at the dot in the centre of the grid, observe the rest of the lines. All the borders should be visible and all the lines straight. If not, retest after a few hours.
Hold the grid at arms length; focus on the black dot in the centre, first with one eye then the other. If the lines are altered or missing or you are having difficulty focussing, stop hydroxychloroquine and notify your doctor.
Periodic blood counts are recommended as antimalarial medications can rarely result in dangerous reduction in cell counts.
- Leukopenia (low white cells)
- Thrombocytopenia (low platelets)
- Aplastic anaemia (all blood cell counts are low)
It is also wise to check renal and liver function before treatment and from time to time.