For over 4 decades the
antimalarial program in India has been prescribing a 5-day
primaquine regimen as an antirelapse
therapy to treat
Plasmodium vivax malaria. In view of conflicting reports on the effectiveness of this regimen in the Indian subcontinent, and the varying prevalence of P. vivax in various ecosystems in India, the antirelapse efficacy of this regimen was evaluated in Orissa, a
malaria endemic state in eastern India where P. falciparum predominates. In 723 cases of P. vivax
infection treated with
chloroquine alone and followed up weekly for 1 yr, the prevalence of recurrence of parasitaemia with
fever was 8.6%. Among another 759 P. vivax cases treated with
chloroquine and a 5-day regimen of
primaquine at 15 mg/day (adult dose), the recurrence of
infection was 6.5%. The difference in recurrence was not significant (P = 0.53). It is important to note that in a great majority of cases of P. vivax in this area,
infection did not recur even without treatment with
primaquine. This finding, that the use of the 5-day
primaquine regimen with
chloroquine had no significant advantage over the use of
chloroquine alone, undermines the rationale of using
primaquine as an antirelapse
drug in forested areas with a high prevalence of P. falciparum.