541 In vitro susceptibility of Gabonese wild isolates of Plasmodium falciparum to artemether, and comparison with chloroquine, quinine, halofantrine and amodiaquine B. PRADINES  *, M. MABIKA MAMFOUMBI, D. PARZY  , M. OWONO MEDANG, C.LEBEAU, J. R. MOUROU MBINA, J. C. DOURY and M.KOMBILA  Unite  de Parasitologie, Institut de Me  decine Tropicale du Service de Sante  des Arme  es, Le Pharo, BP 46, 13998 Marseille, France  De  partement de Parasitologie – Mycologie – Me  decine Tropicale, Faculte  de Me  decine et des Sciences de la Sante  , Libreville, Gabon  Service Me  dical, 6e  me Bataillon d ’Infanterie de Marine, Libreville, Gabon (Received 24 March 1998; revised 2 June 1998; accepted 4 June 1998)  The in vitro activity of artemether against 63 African isolates of Plasmodium falciparum from Libreville, Gabon was evaluated using an isotopic drug susceptibility semi-microtest. The 50 % inhibitory concentration (IC  ) values for artemether were in a narrow range from 08 to 348n (mean IC  50n) and the 95 % confidence interval (CI95 %) was 36–63n. In vitro decreased susceptibility or resistance were observed with artemether (14 %), to chloroquine (90 %), to quinine (32 %). Isolate susceptibility to amodiaquine and halofantrine was high i.e. 100 % and 98 %, respectively. There was a significant positive correlation between responses to artemether and amodiaquine (r  045, P  0001), artemether and chloroquine (r  036, P  0001), artemether and quinine (r  031, P  0001), and artemether and halofantrine (r  019, P  001). Positive correlation between these drugs suggests in vitro cross-resistance or at least common features in drug uptake andor mode of action or resistance. Key words : malaria, Plasmodium falciparum, artemether, chloroquine resistance, Gabon.  In the absence of effective and practical preventive measures, the only current options for reducing the morbidity and mortality of malaria, especially in Africa, are chemoprophylaxis and chemotherapy. The emergence of Plasmodium falciparum resistance to the standard anti-malarial drugs has led to the use of artemisinin and its derivatives as first-line drugs in southeast Asia. Artemether (an oil-soluble arte- misinin-derivative) has also been registered in some parts of Africa and especially in Gabon. With the exception of a few reference strains and isolates of P. falciparum (Alin, Bjorkman & Ashton, 1990 ; Bustos, Gay & Diquet, 1994 (Philippines) ; Basco & Le Bras, 1994 (Cambodia)), the in vitro response pattern of artemether to wild isolates in Africa (Basco & Le Bras, 1993 ; Pradines et al. 1998 (Senegal)) particularly in Gabon has not been assessed. The artemisinin derivatives, including artemether, which act more rapidly against P. falciparum than other anti-malarial drugs, have proven efficacy in the treatment of severe malaria in * Corresponding author : Unite  de Parasitologie, Institut de Me  decine Tropicale du Service de Sante  des Arme  es, La Pharo, BP46, 13998 Marseille, France. Tel : 33 4 91 15 01 50. Fax : 33 4 91 59 44 77. E-mail : imtssagulliver.fr adults in Asia (Hien et al. 1996 ; Vinh et al. 1997) and in children with cerebral malaria in Africa (Boele van Hensbroek et al. 1996; Murphy et al. 1997). The present study assesses the in vitro suscep- tibility of Gabonese wild isolates of P. falciparum to artemether, chloroquine, quinine, halofantrine and amodiaquine. Any in vitro cross-resistance patterns among these compounds were also investigated.    Isolates of P. falciparum Between April and July 1997 we analysed the drug sensitivity patterns of 63 fresh P. falciparum isolates obtained from hospitalized children (6 months–15 years old) with uncomplicated or severe malaria from Libreville (Gabon). Venous blood was collected before treatment in Vacutainer R ACD tubes (Becton Dickinson, Rutherford, NJ, USA) and transported at 4 C to Marseille within 96 h. Thin blood smears were stained using an RAL R kit (Re  actifs RAL, Paris, France) and examined to determine parasite density and to confirm monoinfection by P. fal- ciparum. Samples with parasitaemia ranging from 003 to 78 % were used to test drug sensitivity. Parasitized erythrocytes were washed 3 times in Parasitology (1998), 117, 541–545. Printed in the United Kingdom  1998 Cambridge University Press