Since artemisinin shows low solubility

Since artemisinin shows low solubility and poor oral bioavailability [8], [9], derivatizations of artemisinin were carried out and yielded different semisynthetic antimalarial drugs such as artemether and sodium artesunate. Artemether (decahydro-10-methoxy-3,6,9-trimethyl-3,12-epoxy-12H-pyrano [4.3-j]-1,2-benzodioxepin) (Fig. 1) is more active than the parent Aprotinin artemisinin [10]. Artemether is practically insoluble in water, very soluble in dichloromethane and acetone, freely soluble in ethyl acetate and dehydrated ethanol and shows a higher stability when dissolved in oils. The antimalarial action of artemether appears like artemisinin to be mediated by the generation of free radicals from the endoperoxy bridge of the drug. This endoperoxy bridge is essential for antimalarial activity because experiments with compounds having only one oxygen instead of two showed no activity [11]. The combination of artemether with lumefantrin is a well-tolerated, fast acting and effective blood schizontocidal drug. It is useful mainly in the treatment of uncomplicated P. falciparum malaria that is resistant to other antimalarial drugs [12]. Both for quality assurance and consumer safety the quantification of artemether in its commercial pharmaceutical products is particularly important. Suggested methods of determining the quantity of artemether are complex chromatographic (HPLC, TLC scanning) and NMR methods [13], [14], [15]. The analyses of artemether in tablets and/or capsules is till now carried out by using TLC, HPLC, TLC scanning techniques and one spectrophotometric method [14], [16], [17], [18]. The purpose of the present study was to develop and validate an analytical method for the determination of artemether. The method ought to be not time-consuming and simple and therefore suitable in routine work. Since artemether contains the electrochemically active peroxide (–O–O–) group it can be reduced easily at various electrodes [19], [20], [21], [22], [23], [24]. On the basis of these considerations, the electrochemical behaviour of artemether at a mercury electrode was studied in order to develop a differential pulse polarographic method. Then as a proof of principle the estimated method was tested in the mono-preparation Artemos® and in the compound preparation Riamet®.
Experimental
Results and discussion
Conclusions In summary, a simple differential pulse polarographic method has been developed for the determination of artemether in pharmaceutical formulations. The significant advantage of this DPP method is that the analysis requires neither extensive separation nor extraction of artemether, with the result that the method is selective without being time consuming. In addition the established method is robust, not expensive and suitable for routine analysis which is reflected in the successful analysis of Riamet® tablets and Artemos® soft gel capsules. Furthermore the relative standard deviation of ±1.01% for Riamet® and ±0.53% for Artemos® indicates an excellent reproducibility. Since the proposed method is not very temperature sensitive it is applicable in all climate zones of the earth, thus making it suitable for quality assurance of malaria drugs in the known risk areas.
Introduction The selection of populations resistant to standard regimens of chemotherapy has led to a major public health problem in many regions where falciparum malaria is common. Currently, most of the drugs that have been used in the past to treat or prevent malaria are no longer effective 1, 2. It is critical to increase chemotherapeutic options by identifying new drugs and drug targets, and optimizing deployment of drugs that are already in use. Two drugs that have been used widely against malaria are pyrimethamine and proguanil (which is metabolized in humans into the active form, cycloguanil [1]). These are both competitive inhibitors of the enzyme dihydrofolate reductase (DHFR; 5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) that controls a key step in thymidylate biosynthesis [3]. Drug screening studies have identified many other DHFR inhibitors that are effective in vitro against P. falciparum4, 5, 6, but the rapid selection of resistance to pyrimethamine and cycloguanil has strongly discouraged further development. The assumption is that other drugs with a mode of action similar to pyrimethamine and cycloguanil would show equally strong selection for drug resistance, but it has not been possible to test this directly.