Toxicity related to chloroquine treatment of resistant vivax malaria

To report a case of severe chloroquine toxicity in the presence of high-grade chloroquine-resistant Plasmodium vivax.

A febrile 36-year-old seaman from Mumbai (Bombay) was prescribed >5 times the usual dose of chloroquine for malaria diagnosed empirically onboard ship. His fever resolved, but he developed symptoms consistent with those of chloroquine toxicity. Fever recurred 30 days after his initial presentation, and blood smear-positive vivax malaria was diagnosed. A serum chloroquine concentration at this time (91 micro g/L) was above that considered effective for chloroquine-sensitive P. vivax (>15 micro g/L). The patient responded to atovaquone plus proguanil followed by primaquine.

The patient was given chloroquine by his captain in a dosage regimen appropriate for quinine (2 tablets 3 times daily for 7 d). Pharmacokinetic modeling suggested that the patient's initial over-treatment was as reported and that the predicted maximum serum concentration of chloroquine (902 micro g/L) was within the range seen in fatal chloroquine overdose.

Chloroquine-resistant vivax malaria is increasingly widespread, and transmission can occur within large tropical population centers. For drugs with a narrow therapeutic index such as chloroquine, recommended dosing regimens should be respected, and adequate information sources must be available where such drugs are dispensed by untrained personnel.