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Instead of taking 500 mg weekly, the recommended dose for prophylaxis, the patient took 500 mg of chloroquine phosphate daily, starting 1 week before the trip, during the 2 weeks in Costa Rica, and for 1 week after returning home. She had taken the first dose 3.5 months before presentation. Hair hypopigmentation is a rare but reversible side effect of chloroquine.
Although most cases occur after 3 consecutive months of treatment with daily doses of more than 500 mg of the drug, rapid onset is also possible.