Chloroquine

What chloroquine is used for

Chloroquine is an antimalarial tablet used to treat malaria attacks and, taken weekly, to prevent them. It also kills the amoeba behind amoebiasis, a gut infection, and it damps an overactive immune response — the job it does in lupus, where the immune system turns on the body's own tissues, and less often in rheumatoid arthritis and sarcoidosis. Lupus treatment is usually a lower daily dose, continued for months or years.

Inside red blood cells the malaria parasite feeds on haemoglobin and turns what is left of it into a harmless pigment. Chloroquine jams that conversion, so the toxic pigment accumulates and the parasite dies. It only helps where the local parasite is still vulnerable, and resistance among falciparum malaria — the most dangerous kind — is now widespread.

If you are travelling to a malaria area

Prevention is one tablet a week, always on the same weekday. Start a week or two before you arrive, keep going while you are in the area, and carry on with the weekly dose for several weeks after you leave. A malaria attack is treated on a different pattern: a dose straight away, half that dose six to eight hours later, then half the dose once a day for the next two days. An upset stomach and nausea often show up in the first days; a meal or a glass of milk with the tablet makes that easier, and each dose goes down with water.

Aralen and Chloroquine: two names, one medicine

Both products are chloroquine phosphate tablets in 250mg and 500mg: Aralen and Chloroquine. Aralen is a brand name; chloroquine is the plain one. Of the two strengths, 500mg carries the larger dose. Both sit in the antiparasitics range, and the tablets keep well away from heat, damp and bright light.

Side effects worth knowing

The first days often bring nausea, vomiting, stomach pain, headache, dizziness and blurred vision, which usually settle. Itching can be intense, especially for people with darker skin, and some notice their hair lightening. Less often, chloroquine disturbs the heart's rhythm, giving a racing or irregular beat, or drops blood sugar low enough to bring on shaking, sweating and confusion. Some people notice ringing or muffled hearing, muscle weakness, or a change in mood or behaviour — signs that the medicine is not suiting them. Long courses carry a risk to the retina, the light-sensitive layer at the back of the eye, where the medicine builds up over months and can harm sight. If your face, lips or throat swell after a tablet, that is an emergency.

What interacts with chloroquine

Antacids and kaolin powder reduce how much chloroquine reaches the blood, so give them a few hours either side of your dose. Cimetidine, a stomach-acid medicine, makes chloroquine linger in the body longer. Chloroquine's effect on heart rhythm stacks with that of amiodarone, some antipsychotics and certain antibiotics.