Drug resistance: malaria
Antimalarial drug resistance is a major public health problem which hinders the control of malaria. The WHO publication, Drug resistance in malaria, describes the state of knowledge about this problem and outlines the current thinking regarding strategies to limit the advent, spread and intensification of drug-resistant malaria.
Resistance is spreading
Resistance of Plasmodium falciparum to choloroquine, the cheapest and the most used drug is spreading in almost all the endemic countries. Resistance to the combination of sulfadoxine-pyrimethamine which was already present in South America and in South-East Asia is now emerging in East Africa.
The problem of antimalarial drug resistance is aggravated by the existence of cross resistance among drugs belonging to the same chemical family.
Objectives of monitoring antimalarial drug resistance
- Evaluate the efficacy of first- and second-line drugs used in the treatment of malaria
- Provide information for action: provide good quality data to ministries of health in countries in order to update their drug policies.
Tools for monitoring
1. Therapeutic efficacy tests
In 1996, WHO had developed a protocol for assessing the therapeutic efficacy of antimalarial drugs for the treatment of falciparum malaria in intense transmission areas.
During the WHO consultation on antimalarial drug resistance held in December 2001, this protocol has been updated. During the same meeting, a protocol for assessing the therapeutic efficacy of antimalarial drugs for the treatment of falciparum malaria in low to moderate transmission areas as well as a protocol for assessing the efficacy of chloroquine for the treatment of Plasmodium vivax have been discussed.
Assessment of therapeutic efficacy of antimalarial drugs for uncomplicated falciparum malaria in areas with intense transmission
- Antimalarial drug resistance protocol
Other tools can be used for research as well as for early warning systems.
2. In vitro tests
The most commonly used methods for the antimalarial in vitro testing are the in vitro micro-test Mark III the isotopic test and drug sensitivity assay based on the measurement of HRP2/or pLDH/ in an enzyme-linked immunosorbent assay (ELISA). In vitro pre-dosed plates for the assessment of parasite in vitro susceptibility to antimalarial drugs can be purchased through the Vector Control Research Unit, Universiti Sains Malaysia, Penang, Malaysia under the auspices of WHO.
3. Molecular markers
Molecular markers of P. falciparum resistance are available for only a few drugs (chloroquine, pyrimethamine, cycloguanil, sulfadoxine, atovaquone), while for others they are not yet determined. WHO in collaboration with the WHO Regional Offices is assisting countries in training the medical staff on standardized protocols and in analysing the data. Standardized data entry programmes for the therapeutic efficacy test, for the WHO in vitro test and Probit calculus sheets are available.