Tanzanian medicinal plants were extracted and tested for in vitro antimalarial activity, using the multidrug resistant K1 strain of Plasmodium falciparum. Of 49 plants investigated, extracts of three plants were found to have an IC50 between 5-10 micrograms/ml, extracts of 18 other plants showed an IC50 between 10 and 50 micrograms/ml, all others were less active. The three most active extracts were obtained from the tubers of Cyperus rotundus L. (Cyperaceae), the rootbark of Hoslundia opposita Vahl. (Labiatae), and the rootbark of Lantana camara L. (Verbenaceae).

Pure compounds were isolated from plant extracts with antimalarial activity. The extracts were obtained from the tubers of Cyperus rotundus L. (Cyperaceae), the rootbark of Zanthoxylum gilletii (De Wild) Waterm. (Rutaceae), and the rootbark of Margaritaria discoidea (Baill.) Webster (Euphorbiaceae). The most active compounds included (IC50 within brackets): alpha-cyperone (1) (5.5 micrograms/ml), N-isobutyldeca-2,4-dienamide (2) (5.4 micrograms/ml), and securinine (3) (5.4 micrograms/ml). A mixture of autoxidation products of beta-selinene was found to be the most active antimalarial substances obtained from C. rotundus (5.6 micrograms/ml.

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The sensitivity of Plasmodium falciparum to chloroquine was tested in Muheza, Pangani, Tanga and Korogwe districts in north-eastern Tanzania by applying both in vivo and in vitro tests in schoolchildren. A total dose of 25 mg chloroquine base/kg body-weight given over a period of three days (10 mg/kg on days 0 and one; and 5 mg/kg on day 2) failed to clear asexual parasites from the peripheral blood by day 7 in 12.5% of the children tested at Muheza, 5.9% at Pangani, 31.8% at Tanga, and 39.5% at Korogwe. In vitro micro tests were successfully carried out on 44 isolates at Muheza, 29 isolates at Pangani, 45 isolates at Tanga and 44 isolates at Korogwe. Schizont maturation at chloroquine concentrations of 1.14 mu mol/litre of blood and above, an indication of drug resistance, was observed in 20.5% of the isolates at Muheza, 41.4% at Pangani, 51.1% at Tanga and 45.5% at Korogwe. In vivo and in vitro results of the tests for resistance have been compared.