Chloroquine - Adverse Effects

Adverse Effects

At the doses used for prevention of malaria, side effects include gastrointestinal problems, stomach ache, itch, headache, postural hypotension, nightmares and blurred vision.

Chloroquine-induced itching is very common among black Africans (70%), but much less common in other races. It increases with age, and is so severe as to stop compliance with drug therapy. It is increased during malaria fever; its severity is correlated to the malaria parasite load in blood. Some evidence indicates it has a genetic basis and is related to chloroquine action with opiate receptors centrally or peripherally.

When doses are extended over a number of months, a slow onset of mood changes (i.e., depression, anxiety) can occur. These may be more pronounced with higher doses used for treatment. Chloroquine tablets have an unpleasant metallic taste.

Another serious side effect is toxicity to the eye (specifically, central serous retinopathy). This only occurs with long-term use over many years. Patients on long-term chloroquine therapy should be screened at baseline and every five years. The daily safe maximum doses for eye toxicity can be computed from one's height and weight using this calculator.

Chloroquine is very dangerous in overdose. It is rapidly absorbed from the gut. In 1961, published studies showed three children who took overdoses died within 2.5 hours of taking the drug. While the amount of the overdose was not cited, the therapeutic index for chloroquine is known to be small.

According to research published in the journal PLoS ONE, an overuse of chloroquine treatment has led to the development of a specific strain of E. coli that is now resistant to the powerful antibiotic ciprofloxacin.

A metabolite of chloroquine - hydroxycloroquine - has a long half-life (32–56 days) in blood and a large volume of distribution (580-815 L/kg). The therapeutic, toxic and lethal ranges are usually considered to be 0.03 to 15 mg/l, 3.0 to 26 mg/l and 20 to 104 mg/l, respectively. However, nontoxic cases have been reported in the range 0.3 to 39 mg/l, suggesting individual tolerance to this agent may be more variable than previously recognised.