- Email: [email protected]
Rational use of drugs against Plasmodium falciparum
TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE (2001)95,345-346
Rational
use of drugs against
D. C. Warhurst* Tropical Medicine,
and M. T. Duraisingh London WClE 7HT, UK
Plasmodium Department
falciparum
of Infectious and Tropical Diseases, London School of Hygiene and
Abstract
Recent studies on resistance to blood schizontocides in Plasmodium falciparum give a rational basis for the use of artemisinins combined with arylaminoalcohols for the treatment of uncomplicated chloroquineresistant malaria in Africa. In areas where such combinations are introduced, there is reason to believe that the continued use of chloroquine in the community will help protect the new drugs from resistance. In view of several laboratory studies, combinations of artemisinins with antifolates or chloroquine pose a risk of antagonistic interaction. This can be avoided by use of the artemisinin and the companion drug sequentially. malaria, Plasmodium falciparum, chemotherapy, drug choice, drug combinations, drug resistance, artemisinin, arylaminoalcohols, Africa
Keywords:
Recent research reports (DURAISINGH et al., 2000; F&ED that 2 major groups of antimalarial blood schizontocidal drugs interact in different ways with Plasmodium falciparum PGH-1 protein (specified by the gene Pfmdrl on chromosome 5 and analogous to MDR, the drug-export protein found in cancer cell membranes). These are: et al., 2000) have demonstrated
(i) the 4-aminoquinoline alkaloid quinine,
chloroquine and the cinchona
and (ii) the artemisinin derivatives and the synthetic arylaminoalcohols, mefloquine, halofantrine and lumefantrine. High levels of resistance to chloroquine, and moderate resistance to quinine, are associated with point mutations in Pjkndrl, specifying an altered PGH-1. Resistance to artemisinins in vitro, and to the synthetic arylaminoalcohols is associated with wild-type Pfmdrl specifying normal PGH- 1. The simple conclusion from these observations is that chloroquine-resistant strains of I? falciparum should be sensitive to artemisinins (such as artemether and artesunate) and arylaminoalcohols (such as mefloquine, halofantrine and lumefantrine). It must however be borne in mind that this conclusion may not apply in parts of South-East Asia, where amplification of Pfmdrl is prevalent, and increased production of PGH-1 by l? falciparum is apparently responsible for chloroquineand quinine-resistance co-existing with resistance to artemisinins and arylaminoalcohols (PRICE et al., 1999). This interpretation is supported by observations of invitro cross resistance reported from Africa (PRADINES et al., 1998). Therefore one can predict that in parts of Africa where high-level chloroquine-resistance is prevalent, artemisinins and arylaminoalcohols are likely to be more effective than in areas where chloroquine resistance is less common. In view of the short half-life of artemisinins and the consequent tendency for infections to recrudesce after clinical cure, use in combination with other, sloweracting drugs has been found valuable (artesunateimefloquine and artemetherilumefantrine (VON SEIDLEIN et al., 1998; WHITE et al., 1999). Known potentiative interactions between artemisinin derivatives and arylaminoalcohols, especially where there is some artemisinin- or mefloquine-resistance, enhance the value of this approach (CHAWIRA et al., 1987; HASSAN ALIN et al., 1999). The relatively low, -2-fold degree of resistance seen to artemisinins, which have intrinsically high activity, means that the major impact of PGH-l-associated resistance falls on the mefloquine or lumefantrine component.
*Author for correspondence; e-mail [email protected]
The above argument, based on recent insights into the mechanism of resistance to blood schizontocides, supports the use of artemisinins and arylaminoalcohols in combination for the treatment of uncomplicated chloroquine-resistant malaria in Africa. Clearly, apart from concerns with the affordability of these approaches, there is a worry that with increasing use of such combinations, multidrug resistance, as seen in South-East Asia, will become widespread. There are grounds for predicting that the rise of multidrug resistance will be slower in Africa than in South-East Asia. In hyper- or holo-endemic African populations, parasite-carriers undergoing drug treatment are rare compared with asymptomatics who have not sought treatment. This provides a large mosquitoinfective reservoir of parasites unexposed and still sensitive to a newly introduced combination. In contrast, in Thai-border areas the entomological inoculation rate is low, most persons are effectively non-immune, and parasite-carriers tend to be both symptomatic and seeking treatment. Most of the mosquito-infective parasites will have been exposed to drug. Although the argument applies most clearly to new &ugs with short half-life (WATKINS & MOSOBO. 1993) it could also exnlain the temporal difference in ‘onset ‘of chloroquine-resistance between Africa on the one hand, and South America and South-East Asia on the other. This approach resembles the ‘refugium’ concept in controlling insecticide resistance (e.g. FISCHHOFF, 1996). It follows from this argument and the observations on reciprocal cross-resistance made above, that in an African setting where chloroquine is beginning to fail in children, its continued use will help prevent development of resistance to an alternative based on the artemisininwith-arylaminoalcohol model. This view is supported by observations of selection of chloroquine-resistance (coartemether-sensitivity) determinants in Pjmdrl during chloroquine treatment (DURAISINGH et aZ., 1997) and of co-artemether-resistance (chloroquine-sensitivity) determinants during co-artemether treatment (DURAISINGH, 1999). In South-East Asia where amplified pfmdrl is common, resistance in vitro to artemisinins and arylaminoalcohols individually is alleviated by use in combinations, and artesunateimefloquine and co-artemether (artemether/lumefantrine) are effective, although increased dosage is necessary for the latter (VAN VUGT et al., 1999).
The recently described determinant of chloroquineresistance, a lys76thr change in the PfCRT protein, promises to be the permissive mutation for chloroquine-resistance (FIDOCK et al., 2000). Although of great importance, this change alone is associated with a modest decrease in chloroquine-sensitivity, leading to RI or late recrudescence RI resistance. We do not expect that the impact of this new determinant will significantly alter the above argument, since the most acute effects of chloroquine-resistance are due to early treatment failure
D. C. WARHURST AND M. T. DURAISINGH
346
which is likely to be associated with PGHl changes following the PfCRT change. The testing of artemisinins in combination with all existing antimalarial drugs is in progress as a WHO initiative, because of the clear advantage of the artemisinin-related rapid reduction of the parasite biomass by a factor of -1 O4per cycle (WHITE, 1998) and consequent reduction of the chance of selection of a resistant mutation from a reduced population of 10 000 or fewer (WHITE et al., 1999) by the drug used in combination. In addition, artemisinins, probably because of their huge effect on the growing parasite-population, reduce the gametocvte load and this has been associated in Thailand Gith a reduction in transmission (PRICE et aZ., 1996). Similar observations on gametocgte reduction have been reported for co-artemether (VON SEIDLEIN et al., 1998). Althouch all uossible combination studies should be carried out, problems will probably arise, in particular with the antifolates, including pyrimethamine and sulfadoxine, where mouse work with P. berghei and l? yoelii (CHAWIRA et al., 1987) and experiments in vitro on l? falciparum have demonstrated antagonism. Furthermore, antagonism between chloroquine and artemisinins has been reported in vitro in l? falcipavwn (FIVBLMAN et al., 1999). Most of these features were reuorted in the 1980s in the original Chinese work on akemisinin. Although there a&some plausible ideas about the mechanism of antagonism by chloroquine, the reason for antagonism by antifolates is still under investigation. The use of artesunate combined with pyrimethaminesulfadoxine, compared with pyrimethamine-sulfadoxine alone, in a recent clinical trial in The Gambia (VON SEIDLEIN
et aZ., 2000) was less successful
than expected.
Parasite clearance time was reduced by the combination, and gametocyte carriage was reduced. Other clinical outcome features were no different. To be fair, in this trial, pyrimethamine-sulfadoxine alone was very effective, rendering
comparison
difficult.
However,
if antag-
onisms should arise in these studies, the half-lives of artemisinins are so short that giving the companion drug the day after starting the artesunate course, where practicable, should avoid most of the antagonism. References Chawira, A. N., Warhurst, D. C., Robinson, B. & Peters, W. (1987). The effect of combinations of qinghaosu (artemisinin) with standard antimalarial drugs-in- the suppressive treatment of malaria in mice. Transactions ofthe Royal Society of TropicalMedicine and Hygiene, 81, 554-558. Duraisingh, M. T. (1999). Characterisation of resistance to artemisinin in Plasmodium falciparum. PhD Thesis, University of London, UK. Duraisingh, M. T., Drakeley, C. J., Muller, O., Bailey, R., Snounou, G., Targett, G. A., Greenwood, B. M. & Warhurst, D. C. (1997). Evidence for selection for the tyrosine-86 allele of the pfmdr 1 gene of Plasmodium falciparum by chloroquine and amodiaquine. Parasitology, 114,205-211. Duraisingh, M. T., Roper, C., Walliker, D. & Warhurst, D. C. (2000). Increased sensitivity to the antimalarials mefloquine and artemisinin is conferred by mutations in the pfmdrf gene of Plasmodium falciparum. Molecular Microbiology, 36, 955961. Fidock, D. A., Nomura, T., Talley, A. K., Cooper, R. A., Dzekunov, S. M., Ferdig, M. T., Ursos, L. M. B., Sidhu, A. B. S., Naude, B., Deitsch, I<. W., Su, X.-Z., Wooton, J. C.,
Roepe, P. D. & Wellems, T. E. (2000). Mutations in the P. fulciaarum digestive vacuole transmembrane orotein PfCRT ‘and-evidence-for their role in chloroquine-resistance. Molecularcell, 6, 861-871. Fischhoff, D. A. (1996). Insect resistant crop plants. In: Biotechnology and Integrated Pest Control, Persley, G. J. (editor). Wallinaford: C.A.B. International. Chaoter 12. Fivelman, Q. c.:.,Walden, J. C., Smith, P. J:, Folb, P. I. &Barnes, K. I. (1999). The effect of artesunate combined with standard antimalarials against chloroquine-sensitive and chloroquineresistant strains of Plasmodiumfalciparum in vitro. Transactions of the Royal Society of Tropical Medicine and Hygiene, 93,429432. Hassan Alin, M., Bjorkman, A. & Wernsdorfer, W. H. (1999). Synergism of benflumetol and artemether in Plasmodium falciparum. AmericanJournal of Tropical Medicine and Hygiene, 61,439-445. Pradines, B., Rogier, C., Fusai, T., Tall, A., Trape, J. F. & Doury, J. C. (1998). In vitro activity of artemether against African isolates (Senegal) of Plasmodium fulciparum in comparison with standard antimalarial drugs. AmericanJournal of Tropical Medicine and Hygiene, S&354-357. Price. R. N.. Nosten. F.. Luxemburaer. C.. ter Kuile. F. 0.. Paiphun, L., Chongsuphajaisiddhi,T.& White, N. J. (1996): Effects of artemisinin derivatives on malaria transmissibility. Lance& 341, 1654- 1658. Price, R. N., Cassar, C., Brockman. A., Duraisineh. M., van Vu-&, M., White, N. J.,-Nosten, F. 8r K&shna,S. (11999).‘The pfmdrl gene is associated with a multidrug-resistant phenotype in Plasmodium falciparum from the western border of Thailand. Antimicrobial Agents and Chemotherapy, 43, 29432949. Reed, M. B., Saliba, K. J., Caruana, S. R., Kirk, K. & Cowman, A. F. (2000). Pghl modulates sensitivity and resistance to multiple antimalarials in Plasmodiumfalciparum. Nature, 403, 906-909. Van Vugt, M. V., Wilairatana, P., Gemperli, B., Gathmann, I., Phaipun, L., Brockman, A., Luxemburger, C., White, N. J., Nosten, F. & Looareesuwan, S. (1999). Efficacy of six doses of artemether-lumefantrine (benflumetol) in multidrugresistant Plasmodium falciparum malaria. American Journal of Tropical Medicine and Hygiene, 60, 936-942. Von Seidlein, L., Bojang, K., Jones, I’., Jaffar, S., Pinder, M., Obaro, S., Doherty, T., Haywood, M., Snounou, G., Gemperli, B., Gathmann, I., Royce, C., McAdam, K. & Greenwood, B. (1998). A randomized controlled trial of artemetheri benflumetol, a new antimalarial and pyrimethamineisulfadoxine in the treatment of uncomplicated falciparum malaria in African children. American 7ournal of Tropical Medicine and Hygiene, 58638-644. ” * Von Seidlein, L., Milligan, P., Pinder, M., Bojang, K., Anyalebechi, C., Goslina, R., Coleman, R., Ude, 1. I.. Sadia, A., Duraisingh,.M., W&h&, D., Allot&he, A., Target<- G.; McAdam, K., Greenwood, B., Walraven, G., Olliaro, P. & Doherty, T. (2000). Efficacy of artesunate plus pyrimethamine-sulphadoxine for uncomplicated malaria in Gambian children: a double-blind, randomised, controlled trial. Lancet, 355,352-357. Watkins, W. M. & Mosobo, M. (1993). Treatment of Plasmadium fulciparum malaria with pyrimethamine-sulfadoxine: selective pressure for resistance is a futction of long elimination half-life. Transactions of the Royal Society of Tropical Medicine and Hygiene, 81, 75-78. White, N. J. (1998). Preventing antimalarial drug resistance through combinations. Drug Resistance Updates, 1, 3-9. White, N. J., van Vugt, M. & Ezzet, .F. (1999). Clinical pharmacokinetics and pharmacodynamics of artemethelumefantrine. Clinical Pharmacokinetics, 37, 105 125.
Received 21 November 2000; revised 15 January 2001; acceptedfor publication 18 January 2001
Rational
use of drugs against
D. C. Warhurst* Tropical Medicine,
and M. T. Duraisingh London WClE 7HT, UK
Plasmodium Department
falciparum
of Infectious and Tropical Diseases, London School of Hygiene and
Abstract
Recent studies on resistance to blood schizontocides in Plasmodium falciparum give a rational basis for the use of artemisinins combined with arylaminoalcohols for the treatment of uncomplicated chloroquineresistant malaria in Africa. In areas where such combinations are introduced, there is reason to believe that the continued use of chloroquine in the community will help protect the new drugs from resistance. In view of several laboratory studies, combinations of artemisinins with antifolates or chloroquine pose a risk of antagonistic interaction. This can be avoided by use of the artemisinin and the companion drug sequentially. malaria, Plasmodium falciparum, chemotherapy, drug choice, drug combinations, drug resistance, artemisinin, arylaminoalcohols, Africa
Keywords:
Recent research reports (DURAISINGH et al., 2000; F&ED that 2 major groups of antimalarial blood schizontocidal drugs interact in different ways with Plasmodium falciparum PGH-1 protein (specified by the gene Pfmdrl on chromosome 5 and analogous to MDR, the drug-export protein found in cancer cell membranes). These are: et al., 2000) have demonstrated
(i) the 4-aminoquinoline alkaloid quinine,
chloroquine and the cinchona
and (ii) the artemisinin derivatives and the synthetic arylaminoalcohols, mefloquine, halofantrine and lumefantrine. High levels of resistance to chloroquine, and moderate resistance to quinine, are associated with point mutations in Pjkndrl, specifying an altered PGH-1. Resistance to artemisinins in vitro, and to the synthetic arylaminoalcohols is associated with wild-type Pfmdrl specifying normal PGH- 1. The simple conclusion from these observations is that chloroquine-resistant strains of I? falciparum should be sensitive to artemisinins (such as artemether and artesunate) and arylaminoalcohols (such as mefloquine, halofantrine and lumefantrine). It must however be borne in mind that this conclusion may not apply in parts of South-East Asia, where amplification of Pfmdrl is prevalent, and increased production of PGH-1 by l? falciparum is apparently responsible for chloroquineand quinine-resistance co-existing with resistance to artemisinins and arylaminoalcohols (PRICE et al., 1999). This interpretation is supported by observations of invitro cross resistance reported from Africa (PRADINES et al., 1998). Therefore one can predict that in parts of Africa where high-level chloroquine-resistance is prevalent, artemisinins and arylaminoalcohols are likely to be more effective than in areas where chloroquine resistance is less common. In view of the short half-life of artemisinins and the consequent tendency for infections to recrudesce after clinical cure, use in combination with other, sloweracting drugs has been found valuable (artesunateimefloquine and artemetherilumefantrine (VON SEIDLEIN et al., 1998; WHITE et al., 1999). Known potentiative interactions between artemisinin derivatives and arylaminoalcohols, especially where there is some artemisinin- or mefloquine-resistance, enhance the value of this approach (CHAWIRA et al., 1987; HASSAN ALIN et al., 1999). The relatively low, -2-fold degree of resistance seen to artemisinins, which have intrinsically high activity, means that the major impact of PGH-l-associated resistance falls on the mefloquine or lumefantrine component.
*Author for correspondence; e-mail [email protected]
The above argument, based on recent insights into the mechanism of resistance to blood schizontocides, supports the use of artemisinins and arylaminoalcohols in combination for the treatment of uncomplicated chloroquine-resistant malaria in Africa. Clearly, apart from concerns with the affordability of these approaches, there is a worry that with increasing use of such combinations, multidrug resistance, as seen in South-East Asia, will become widespread. There are grounds for predicting that the rise of multidrug resistance will be slower in Africa than in South-East Asia. In hyper- or holo-endemic African populations, parasite-carriers undergoing drug treatment are rare compared with asymptomatics who have not sought treatment. This provides a large mosquitoinfective reservoir of parasites unexposed and still sensitive to a newly introduced combination. In contrast, in Thai-border areas the entomological inoculation rate is low, most persons are effectively non-immune, and parasite-carriers tend to be both symptomatic and seeking treatment. Most of the mosquito-infective parasites will have been exposed to drug. Although the argument applies most clearly to new &ugs with short half-life (WATKINS & MOSOBO. 1993) it could also exnlain the temporal difference in ‘onset ‘of chloroquine-resistance between Africa on the one hand, and South America and South-East Asia on the other. This approach resembles the ‘refugium’ concept in controlling insecticide resistance (e.g. FISCHHOFF, 1996). It follows from this argument and the observations on reciprocal cross-resistance made above, that in an African setting where chloroquine is beginning to fail in children, its continued use will help prevent development of resistance to an alternative based on the artemisininwith-arylaminoalcohol model. This view is supported by observations of selection of chloroquine-resistance (coartemether-sensitivity) determinants in Pjmdrl during chloroquine treatment (DURAISINGH et aZ., 1997) and of co-artemether-resistance (chloroquine-sensitivity) determinants during co-artemether treatment (DURAISINGH, 1999). In South-East Asia where amplified pfmdrl is common, resistance in vitro to artemisinins and arylaminoalcohols individually is alleviated by use in combinations, and artesunateimefloquine and co-artemether (artemether/lumefantrine) are effective, although increased dosage is necessary for the latter (VAN VUGT et al., 1999).
The recently described determinant of chloroquineresistance, a lys76thr change in the PfCRT protein, promises to be the permissive mutation for chloroquine-resistance (FIDOCK et al., 2000). Although of great importance, this change alone is associated with a modest decrease in chloroquine-sensitivity, leading to RI or late recrudescence RI resistance. We do not expect that the impact of this new determinant will significantly alter the above argument, since the most acute effects of chloroquine-resistance are due to early treatment failure
D. C. WARHURST AND M. T. DURAISINGH
346
which is likely to be associated with PGHl changes following the PfCRT change. The testing of artemisinins in combination with all existing antimalarial drugs is in progress as a WHO initiative, because of the clear advantage of the artemisinin-related rapid reduction of the parasite biomass by a factor of -1 O4per cycle (WHITE, 1998) and consequent reduction of the chance of selection of a resistant mutation from a reduced population of 10 000 or fewer (WHITE et al., 1999) by the drug used in combination. In addition, artemisinins, probably because of their huge effect on the growing parasite-population, reduce the gametocvte load and this has been associated in Thailand Gith a reduction in transmission (PRICE et aZ., 1996). Similar observations on gametocgte reduction have been reported for co-artemether (VON SEIDLEIN et al., 1998). Althouch all uossible combination studies should be carried out, problems will probably arise, in particular with the antifolates, including pyrimethamine and sulfadoxine, where mouse work with P. berghei and l? yoelii (CHAWIRA et al., 1987) and experiments in vitro on l? falciparum have demonstrated antagonism. Furthermore, antagonism between chloroquine and artemisinins has been reported in vitro in l? falcipavwn (FIVBLMAN et al., 1999). Most of these features were reuorted in the 1980s in the original Chinese work on akemisinin. Although there a&some plausible ideas about the mechanism of antagonism by chloroquine, the reason for antagonism by antifolates is still under investigation. The use of artesunate combined with pyrimethaminesulfadoxine, compared with pyrimethamine-sulfadoxine alone, in a recent clinical trial in The Gambia (VON SEIDLEIN
et aZ., 2000) was less successful
than expected.
Parasite clearance time was reduced by the combination, and gametocyte carriage was reduced. Other clinical outcome features were no different. To be fair, in this trial, pyrimethamine-sulfadoxine alone was very effective, rendering
comparison
difficult.
However,
if antag-
onisms should arise in these studies, the half-lives of artemisinins are so short that giving the companion drug the day after starting the artesunate course, where practicable, should avoid most of the antagonism. References Chawira, A. N., Warhurst, D. C., Robinson, B. & Peters, W. (1987). The effect of combinations of qinghaosu (artemisinin) with standard antimalarial drugs-in- the suppressive treatment of malaria in mice. Transactions ofthe Royal Society of TropicalMedicine and Hygiene, 81, 554-558. Duraisingh, M. T. (1999). Characterisation of resistance to artemisinin in Plasmodium falciparum. PhD Thesis, University of London, UK. Duraisingh, M. T., Drakeley, C. J., Muller, O., Bailey, R., Snounou, G., Targett, G. A., Greenwood, B. M. & Warhurst, D. C. (1997). Evidence for selection for the tyrosine-86 allele of the pfmdr 1 gene of Plasmodium falciparum by chloroquine and amodiaquine. Parasitology, 114,205-211. Duraisingh, M. T., Roper, C., Walliker, D. & Warhurst, D. C. (2000). Increased sensitivity to the antimalarials mefloquine and artemisinin is conferred by mutations in the pfmdrf gene of Plasmodium falciparum. Molecular Microbiology, 36, 955961. Fidock, D. A., Nomura, T., Talley, A. K., Cooper, R. A., Dzekunov, S. M., Ferdig, M. T., Ursos, L. M. B., Sidhu, A. B. S., Naude, B., Deitsch, I<. W., Su, X.-Z., Wooton, J. C.,
Roepe, P. D. & Wellems, T. E. (2000). Mutations in the P. fulciaarum digestive vacuole transmembrane orotein PfCRT ‘and-evidence-for their role in chloroquine-resistance. Molecularcell, 6, 861-871. Fischhoff, D. A. (1996). Insect resistant crop plants. In: Biotechnology and Integrated Pest Control, Persley, G. J. (editor). Wallinaford: C.A.B. International. Chaoter 12. Fivelman, Q. c.:.,Walden, J. C., Smith, P. J:, Folb, P. I. &Barnes, K. I. (1999). The effect of artesunate combined with standard antimalarials against chloroquine-sensitive and chloroquineresistant strains of Plasmodiumfalciparum in vitro. Transactions of the Royal Society of Tropical Medicine and Hygiene, 93,429432. Hassan Alin, M., Bjorkman, A. & Wernsdorfer, W. H. (1999). Synergism of benflumetol and artemether in Plasmodium falciparum. AmericanJournal of Tropical Medicine and Hygiene, 61,439-445. Pradines, B., Rogier, C., Fusai, T., Tall, A., Trape, J. F. & Doury, J. C. (1998). In vitro activity of artemether against African isolates (Senegal) of Plasmodium fulciparum in comparison with standard antimalarial drugs. AmericanJournal of Tropical Medicine and Hygiene, S&354-357. Price. R. N.. Nosten. F.. Luxemburaer. C.. ter Kuile. F. 0.. Paiphun, L., Chongsuphajaisiddhi,T.& White, N. J. (1996): Effects of artemisinin derivatives on malaria transmissibility. Lance& 341, 1654- 1658. Price, R. N., Cassar, C., Brockman. A., Duraisineh. M., van Vu-&, M., White, N. J.,-Nosten, F. 8r K&shna,S. (11999).‘The pfmdrl gene is associated with a multidrug-resistant phenotype in Plasmodium falciparum from the western border of Thailand. Antimicrobial Agents and Chemotherapy, 43, 29432949. Reed, M. B., Saliba, K. J., Caruana, S. R., Kirk, K. & Cowman, A. F. (2000). Pghl modulates sensitivity and resistance to multiple antimalarials in Plasmodiumfalciparum. Nature, 403, 906-909. Van Vugt, M. V., Wilairatana, P., Gemperli, B., Gathmann, I., Phaipun, L., Brockman, A., Luxemburger, C., White, N. J., Nosten, F. & Looareesuwan, S. (1999). Efficacy of six doses of artemether-lumefantrine (benflumetol) in multidrugresistant Plasmodium falciparum malaria. American Journal of Tropical Medicine and Hygiene, 60, 936-942. Von Seidlein, L., Bojang, K., Jones, I’., Jaffar, S., Pinder, M., Obaro, S., Doherty, T., Haywood, M., Snounou, G., Gemperli, B., Gathmann, I., Royce, C., McAdam, K. & Greenwood, B. (1998). A randomized controlled trial of artemetheri benflumetol, a new antimalarial and pyrimethamineisulfadoxine in the treatment of uncomplicated falciparum malaria in African children. American 7ournal of Tropical Medicine and Hygiene, 58638-644. ” * Von Seidlein, L., Milligan, P., Pinder, M., Bojang, K., Anyalebechi, C., Goslina, R., Coleman, R., Ude, 1. I.. Sadia, A., Duraisingh,.M., W&h&, D., Allot&he, A., Target<- G.; McAdam, K., Greenwood, B., Walraven, G., Olliaro, P. & Doherty, T. (2000). Efficacy of artesunate plus pyrimethamine-sulphadoxine for uncomplicated malaria in Gambian children: a double-blind, randomised, controlled trial. Lancet, 355,352-357. Watkins, W. M. & Mosobo, M. (1993). Treatment of Plasmadium fulciparum malaria with pyrimethamine-sulfadoxine: selective pressure for resistance is a futction of long elimination half-life. Transactions of the Royal Society of Tropical Medicine and Hygiene, 81, 75-78. White, N. J. (1998). Preventing antimalarial drug resistance through combinations. Drug Resistance Updates, 1, 3-9. White, N. J., van Vugt, M. & Ezzet, .F. (1999). Clinical pharmacokinetics and pharmacodynamics of artemethelumefantrine. Clinical Pharmacokinetics, 37, 105 125.
Received 21 November 2000; revised 15 January 2001; acceptedfor publication 18 January 2001