Chloroquine (Aralen) is one of several 4-aminoquino-line derivatives that display antimalarial activity. Chloroquine is particularly effective against intraeryth-rocytic forms because it is concentrated within the parasitized erythrocyte. This preferential drug accumulation appears to occur as a result of specific uptake mechanisms in the parasite. Chloroquine appears to work by intercalation with DNA, inhibition of heme polymerase or by interaction with Ca++-calmodulin-mediated mechanisms. It also accumulates in the parasite's food vacuoles, where it inhibits peptide formation and phospholipases, leading to parasite death.
The drug is effective against all four types of malaria with the exception of chloroquine-resistant P. falci-parum. Chloroquine destroys the blood stages of the infection and therefore ameliorates the clinical symptoms seen in P. malariae, P. vivax, P. ovale, and sensitive P. fal-ciparum forms of malaria. The disease will return in P. vivax and P. ovale malaria, however, unless the liver stages are sequentially treated with primaquine after the administration of chloroquine. Chloroquine also can be used prophylactically in areas where resistance does not exist. In addition to its use as an antimalarial, chloroquine has been used in the treatment of rheumatoid arthritis and lupus erythematosus (see Chapter 36), extraintestinal amebiasis, and photoallergic reactions.
The absorption of chloroquine from the gastrointestinal tract is rapid and complete. The drug is distributed widely and is extensively bound to body tissues, with the liver containing 500 times the blood concentration. Such binding is reflected in a large volume of distribution (Vd). Desethylchloroquine is the major metabolite formed following hepatic metabolism, and both the parent compound and its metabolites are slowly eliminated by renal excretion. The half-life of the drug is 6 to 7 days.
Dizziness, headache, itching (especially in dark-skinned people), skin rash, vomiting, and blurring of vision may occur following low doses of chloroquine. In higher dosages these symptoms are more common, and exacerbation or unmasking of lupus erythematosus or discoid lupus, as well as toxic effects in skin, blood, and eyes can occur. Since the drug concentrates in melanin-containing structures, prolonged administration of high doses can lead to blindness. Chloroquine should not be used in the presence of retinal or visual field changes.
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