In vitro activity of new artemisinin derivatives against Plasmodium falciparum clinical isolates from Gabon.

Nowadays, artemisinins are the mainstay of malaria treatment, but initial indications of resistance against clinically used derivatives are present. In this study, ten new artemisinin derivatives were tested in vitro against Plasmodium falciparum laboratory strains as well as clinical isolates from Gabon. All derivatives were highly active, with 50% inhibitory concentrations (IC(50) values) <13 nM in the clinical isolates. The activity of one fluoro-containing derivative did not correlate with that of the parent compound, suggesting a different activity profile. New artemisinin derivatives with different activity profiles are of special interest as they represent an important class of candidates for pre-clinical testing in clinical parasite isolates adapted to currently used artemisinins, since derivatisation is one possible strategy to prolong the clinical usefulness of this important class of antimalarials.

Efficacy and safety of a fixed dose artesunate-sulphamethoxypyrazine-pyrimethamine compared to artemether-lumefantrine for the treatment of uncomplicated falciparum malaria across Africa: a randomized multi-centre trial.

BACKGROUND: The efficacy of artemisinin-based combination therapy has already been demonstrated in a number of studies all over the world, and some of them can be regarded as comparably effective. Ease of administration of anti-malarial treatments with shorter courses and fewer tablets may be key determinant of compliance. METHODS: Patients with uncomplicated falciparum malaria and over six months of age were recruited in Cameroon, Mali, Rwanda and Sudan. 1,384 patients were randomly assigned to receive artesunate-sulphamethoxypyrazine-pyrimethamine (AS-SMP) three-day (once daily for 3 days) regimen (N = 476) or AS-SMP 24-hour (0 h, 12 h, 24 h) regimen (N = 458) or artemether-lumefantrine (AL), the regular 6 doses regimen (N = 450). The primary objective was to demonstrate non-inferiority (using a margin of -6%) of AS-SMP 24 hours or AS-SMP three days versus AL on the PCR-corrected 28-day cure rate. RESULTS: The PCR corrected 28-day cure rate on the intention to treat (ITT) analysis population were: 96.0%(457/476) in the AS-SMP three-day group, 93.7%(429/458) in the AS-SMP 24-hour group and 92.0%(414/450) in the AL group. Likewise, the cure rates on the PP analysis population were high: 99.3%(432/437) in the AS-SMP three-day group, 99.5%(416/419) in the AS-SMP 24-hour group and 99.7(391/394)% in the AL group. Most common drug-related adverse events were gastrointestinal symptoms (such as vomiting and diarrhea) which were slightly higher in the AS-SMP 24-hour group. CONCLUSION: AS-SMP three days or AS-SMP 24 hours are safe, are as efficacious as AL, and are well tolerated. TRIAL REGISTRATION: NCT00484900 http://www.clinicaltrials.gov.

Optimization of an LC-MS method for the determination of artesunate and dihydroartemisinin plasma levels using liquid-liquid extraction.

Artesunate is a derivate of artemisinin, an antimalarial drug used for the treatment of malaria caused by Plasmodium falciparum and related parasites. Artesunate is hydrolyzed rapidly to dihydroartemisinin in vivo. It has been found that artemisinin and its derivatives may have neurotoxic effects. A method was developed to analyze human plasma samples for the contents of artesunate and dihydroartemisinin. The plasma samples are extracted with ethyl acetate, concentrated, and redissolved in water/acetonitrile. Analyses was performed with liquid chromatography-mass spectrometry using a binary gradient program with aquaeous formic acid and acetonitrile formic acid on a XTerra MS C18-column. The mass spectrometer was operated in the positive atmospheric pressure chemical ionization mode with single ion recording. The lower limits of detection were 10 and 25 ng/mL plasma for DHA and artesunate, respectively. The method was validated according to the guidelines for validation of bioanalytical methods.

Chemical instability determines the biological action of the artemisinins.

Artemisinin is a sesquiterpene compound of plant origin. It has a low molecular weight, and it contains five oxygen atoms, two in a lactone function, one is part of a seven membered ring system and two forms a peroxide function bridging over the seven-membered ring. It is a highly energetic molecule prone to lose its activity if circumstances permit. Reduction of its lactone function into dihydroartemisinin makes derivatization easy. Esterification and ether formation contribute to stability. Dihydroartemisinin exists preferably in a beta epimeric format but flip-flops with the alpha epimer. Solvation effects play a role. In doing so, open forms are created and they contribute to the instability, both of the peroxide and of the seven-membered ring. Artemisinins constitute a remarkable class of compounds which display instability both biologically and chemically due to the presence of various functional groups. Activity ranges from a wonderful action against a series of parasites, in particular malaria and schistosomiasis, to bacteria, fungi and selected viruses. The latest developments indicate a potential use in adjuvant cancer chemotherapy. The built-in chemical instability, necessary for biological action, causes serious pharmaceutical problems and only a restricted number of derivatives are useful. Problems are accelerated under tropical conditions and the basic active drug dihydroartemisinin cannot be used as such since it is prone to accelerated breakdown into a series of inactive products. The pitfalls of chemical instability and pharmaceutical stability are discussed in relation to the current uses of the drugs.

Simultaneous quantitative analysis of the antimalarials pyrimethamine and sulfamethoxypyrazine in plasma samples using liquid chromatography/tandem mass spectrometry.

The work presented here deals with the development of a quantitative tool for the simultaneous determination of sulfamethoxypyrazine (sulfalene)/pyrimethamine in plasma. The chromatography used only takes 12.5 min, allowing a fast sample turnover time. Relative standard deviation of retention times was never above 3.48% (n = 66). Adequate sample clean-up was achieved by a simple and relatively fast liquid/liquid extraction. In this way, ionisation suppression effects, typical for more simple sample clean-up procedures, could be avoided resulting in absolute plasma effects of maximum -17.1% for sulfalene, -16.1 for the internal standard (IS), and 12% for pyrimethamine. For both pyrimethamine and sulfalene, quadratic calibration curves from 0.00101 to 0.807 microg/mL for pyrimethamine and from 0.271 to 216 microg/mL for sulfalene gave the best fit. Mean coefficients of determination (R2) were 0.9951 (n = 6, CV% 0.39) for pyrimethamine and 0.9942 (n = 6, CV% 0.13) for sulfalene. Precision was below 9.35% for pyrimethamine and 13.9% for sulfalene. Inaccuracy remained below 15% at all cases. The optimised method was used for a time-course study of the sulfalene/pyrimethamine combination concentration in plasma of patients treated with Co-Arinate, a new curative antimalaria-medicine.