First-time comparison of the in vitro antimalarial activity of Artemisia annua herbal tea and artemisinin

Artemisia annua tea has been proven to be a very effective treatment for malaria in various clinical trials, but to date its efficacy has not been investigated in vitro. A study was therefore performed to evaluate the effects of A. annua tea on Plasmodium falciparum cultures in vitro. The concentration of artemisinin in the herbal tea preparation was also determined. The herbal tea extract was tested against chloroquine (CQ)-sensitive D10 and CQ-resistant W2 strains of P. falciparum using the parasite lactate dehydrogenase assay. Quantification of artemisinin in the extract of leaves of A. annua was performed using proton nuclear magnetic resonance (1H-NMR). Results of the in vitro tests were consistent with the clinical efficacy of A. annua tea [50% inhibitory concentration (IC50) for strain D10 = 1.11 ± 0.21 μg/ml; IC50 for strain W2 = 0.88 ± 0.35 μg/ml]. The concentration of artemisinin in A. annua tea (0.18 ± 0.02% of dry weight) was far too low to be responsible for the antimalarial activity. The artemisinin present in the tea is probably co-solubilised with other ingredients, some of which also have antimalarial activity and act synergistically with it. These compounds also merit further research to determine whether their presence hinders the development of parasite resistance compared with pure artemisinin.