Resurgence of malaria in Mumbai--is escalating chloroquine resistance a cause?

Objectives: Given the steep increase in the incidence of malaria in the city of Mumbai in the nineties, we decided to study the causes for the same as well as analyse the resistance pattern of P. falciparum in the city.
Methods: Smear positive cases of acute uncomplicated P. falciparum malaria who presented to us in 1994, 1995 and 1996 were analysed for their response to full dose chloroquine (25 mg/kg over 3 days). Samples of those patients who satisfied criteria for in vitro resistance testing to chloroquine and other antimalarials, were also studied. Chloroquine level in all patients was studied on Day 3 by HPLC. In vivo response to chloroquine was studied in 30, 71 and 78 patients while in vitro response was studied in 17, 35 and 30 patients respectively in the above years.
Results: We found in vivo chloroquine resistance figures of 36.78%, 45% and 53.8% in the years '94, '95 and '96 and the in vitro resistance figures of 41.17%, 54.28% and 66.6% in the same years.
Conclusions: Our previous studies documenting 15% chloroquine resistance in 1993 and the increasing incidence in subsequent years suggests resistance to chloroquine as one of the causes of resurgence and maintenance of malaria in the city. If patients of uncomplicated P. falciparum malaria are to be treated with chloroquine, rigorous monitoring for nonresponse and timely rescue medication is necessary. Alternative antimalarial drugs such as mefloquine, artemisinin derivatives and sulfadoxine-pyrimethamine should be used in patients where this is not possible.