Efficacy of primaquine regimens for primaquine-resistant Plasmodium vivax malaria in Thailand

To define the current efficacy of Fansidar(R) (F. Hoffmann-La Roche Ltd., B asel Switzerland) (pyrimethamine and sulfadoxine), primaquine in a high dos e, and artesunate for treating acute Plasmodium vivax malaria, we conducted a comparative clinical trial of these 3 drugs in an open-label study. Pati ents (15-65 years old) were assigned to 1 of 4 treatments regimens in a ser ial order. Ninety percent of the patients were infected at Thailand-Myanmar border. Patients in group I (n = 23) received Fansidar(R) (3 tablets, 75 m g of pyrimethamine and 1,500 mg of sulfadoxine, a single dose on the first day), group II (n = 23) received Fansidar(R) (3 tablets, 75 mg of pyrimetha mine and 1,500 mg of sulfadoxine, a single dose on the first day) and then received primaquine (30 mg a day for 14 days), group III (n = 23) received primaquine (30 mg a day for 14 days), and group IV (n = 23) received artesu nate (200 mg once a day for 3 days) and then primaquine (30 mg a day for 14 days). Cure rates on day 28 of follow-up were 40%, 100%, 100%, and 100% in groups I, II, III, and IV, respectively. There were 4 and 5 patients In gr oup I showing post-treatment reappearance of parasitemia at less than or eq ual to 16 days and between 17 and 28 days, respectively. Patients in the ot her 3 groups showed negative parasitemias within 7 days after treatment. Ar tesunate plus primaquine (group IV) cleared parasitemia faster than the oth er 3 regimens. There is a high proportion of ineffectiveness of Fansidar(R) for treatment of P. vivax malaria and it should be no longer used for trea tment of P. vivax malaria acquired at the Thailand-Myanmar border. A high d ose of primaquine is safe and effective in the treatment of P. vivax malari a during the 28-day follow-up period.