The efficacy of a single dose of 45 mg primaquine, as a gametocytocidal agent, was assessed in Mumbai, India, among adults with uncomplicated or severe Plasmodium falciparum malaria. All the patients investigated had been found gametocytaemic, with at least 56 gametocytes/microl blood, within the first 72 h of their illness. Those with uncomplicated malaria, like those with severe malaria, were randomized to receive or not receive primaquine. All the patients were followed up for 29 days post-admission, for gametocytaemia and gametocyte viability (as determined by exflagellation). Among those with uncomplicated malaria, six (27.3%) of the 22 who did not receive primaquine but only one (4.2%) of the 24 who did receive the drug, on day 4, remained gametocytaemic on day 29 (P < 0.05). Similarly, seven (31.8%) of the 22 severe cases who did not receive primaquine but only two (9.5%) of the 21 severe cases who received the drug, on day 8, were found gametocytaemic on day 15 (P < 0.05). While the single, 45-mg dose of primaquine recommended by the World Health Organization was effective in clearing gametocytes from the blood of > 90% of the present cases of malaria, > 4% of the patients with uncomplicated malaria and > 9% of those with the severe disease continued to harbour gametocytes in their peripheral blood 29 and 15 days after taking the primaquine, respectively.

Background: The WHO recommends that adults with uncomplicated P. falciparum successfully treated with a blood schizonticide receive a single dose of primaquine (PQ) 45 mg as a gametocytocidal agent. An earlier pilot study suggested that 75 mg of bulaquine (BQ), of which PQ is a major metabolite, may be a useful alternate to PQ.

We studied the antirelapse efficacy of a supervised 14-d 15 mg/d regimen of primaquine therapy (n = 131) compared with no antirelapse therapy (n = 142) in 273 patients with confirmed Plasmodium vivax malaria in Mumbai, India, between July 1998 and April 2000. There were 6/131 (4.6%) recurrences in patients given primaquine compared with 13/142 (9.2%) in those not given antirelapse therapy. In the 14-d primaquine group, polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) genotyping analysis of pre- and post-treatment blood samples was done for the 6 patients who had a recurrence of parasitaemia and the results gave a true relapse rate of 2.29% (3/131), 2 samples were classified as reinfections and 1 sample did not amplify. Our results indicate probable resistance to the 14-d regimen of primaquine for the first time in India and illustrate the need to (i) monitor patients given this regimen and (ii) carry out comparative studies between primaquine and new drugs such as tafenoquine and bulaquine for preventing relapses.

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Vivax malaria accounts for 80% of malaria cases in Mumbai (Bombay) and has high morbidity. In India, the standard treatment to prevent relapses of vivax malaria is a 5-day regimen of primaquine. However, between 1977 and 1997, the efficacy of this treatment declined from approximately 99% to 87%. The efficacy of the 5-day regimen was therefore compared with that of the 14-day regimen currently recommended by the World Health Organization, in Mumbai. The relapse rates observed, over a 6-month period of follow-up, were 0% with the 14-day regimen, 26.7% with the 5-day, and 11.7% when no primaquine treatment was given. The expenditure incurred on the door-to-door dispensing of the 5-day regimen appears to be without benefit. There is an urgent need to review the present strategy for controlling relapses in vivax malaria, at least for the city of Mumbai, and similar studies need to be carried out in other parts of India, to make all anti-relapse strategies more appropriate.

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