Determination of artemether and dihydroartemisinin in blood plasma by high-performance liquid chromatography for application in clinical pharmacological studies

A high-throughput LC-MS/MS assay for quantification of artesunate and its metabolite dihydroartemisinin in human plasma and saliva

AIM

Saliva is an alternative sampling matrix to plasma, offering a noninvasive technique, but requires a highly sensitive bioanalytical method.

MATERIALS & METHODS

An API 3000 triple quadrupole mass spectrometer with an electrospray ionization source operated in the positive ion mode was used for the analysis.

RESULTS

A high-throughput LC-MS/MS method using SPE for the quantification of artesunate and dihydroartemisinin in plasma and saliva has been optimized and validated according to US FDA guidelines. For both analytes the LLOQ was determined to 5 ng/ml and the calibration range was 5-1000 ng/ml for artesunate and 5-2000 ng/ml for dihydroartemisinin.

CONCLUSION

For the first time, a bioanalytical method for determination of artesunate and dihydroartemisinin in human saliva has been described, showing possible applicability in clinical saliva samples in addition to plasma samples.

Coartemether (artemether and lumefantrine): an oral antimalarial drug

Coartemether (Riamet, Coartem, Novartis), a tablet formulation of artemether and lumefantrine, is a well-tolerated, fast-acting and effective blood schizontocidal drug that serves primarily in the treatment of uncomplicated falciparum malaria that is resistant to other antimalarials. Initial clinical-parasitological response relies mainly on the artemether component, while lumefantrine effects radical cure. The absorption of lumefantrine is poor during the fasting state, the normal condition in acutely ill malaria patients, but with return to normal diet it becomes adequate. This highlights the need for an appropriate adjustment of the dose regimen. In the area where Plasmodium falciparum shows the highest degree of multidrug resistance worldwide, the best results (99% cure) were obtained with a six-dose regimen given over 5 days. Extensive cardiological investigations have demonstrated the high cardiac safety of coartemether.

A liquid chromatographic-tandem mass spectrometric method for determination of artemether and its metabolite dihydroartemisinin in human plasma

BACKGROUND

Artemether-lumefantrine is the most widely recommended artemisinin-based combination treatment for falciparum malaria. Quantification of artemether and its metabolite dihydroartemisinin in biological matrices has traditionally been difficult, with sensitivity being an issue.

RESULTS

A high-throughput bioanalytical method for the analysis of artemether and its metabolite dihydroartemisinin in human plasma using solid-phase extraction in the 96-well plate format and liquid chromatography coupled to positive ion mode tandem mass spectroscopy has been developed and validated according to US FDA guidelines. The method uses 50 µl plasma and covers the calibration range 1.43-500 ng/ml with a limit of detection at 0.36 ng/ml.

CONCLUSIONS

The developed liquid chromatography-tandem mass spectrometry assay is more sensitive than all previous methods despite using a lower plasma volume (50 µl) and is highly suitable for clinical studies where plasma volumes are limited, such as pediatric trials.

TLC-densitometric analysis of artemisinin for the rapid screening of high-producing plantlets of Artemisia annua L

A simple TLC-densitometric technique has been developed for the rapid and accurate analysis of artemisinin in a large number of Artemisia annua plantlets cultured in vitro. This new analytical method is based on the structural conversion of artemisinin on a silica gel layer by ammonia vapour to form 10-azadesoxyartemisinin, a chromophore-containing compound (lambdamax 320 nm) that can be detected by UV-based TLC densitometry. The TLC system was evaluated quantitatively in terms of product stability, precision, accuracy and calibration. Good linearity was obtained in the range of 0.01-0.12 microg artemisinin. The technique appeared to be accurate and sensitive as compared with the complicated pre-column reaction-HPLC technique. Among 90 samples of A. annua plantlets, the artemisinin content in the leaves appeared to be highly variable, ranging from 0.02 to 0.67% w/w dry weight. These results demonstrate that densitometric TLC can be a cheap and simple technique for the accurate screening of high-artemisinin-producing plants.

Assay of artemether, methylparaben and propylparaben in a formulated paediatric antimalarial dry suspension

Two HPLC-UV methods are described for the separate determination of artemether (AM) and the combined preservatives, methylparaben and propylparaben in a pharmaceutical dosage form. These analytes are contained in a dry suspension with a high amount of non-soluble excipients, some of which can interfere with the analysis. This makes their separation and analysis of the actives complex. Moreover, due to the wide difference in concentrations, the three analytes could not be quantitated simultaneously. Artemether was analysed using a reversed-phase Nucleosil C(18) column [5 microm, 125 mm x 4 mm (i.d.)] with a mixture of acetonitrile: potassium phosphate buffer pH 5.0 (0.05 M): water [48:32:10 (v/v/v)] as mobile phase. Due to the low solubility of the hydroxy benzoic acid esters in water, their sodium salts were used in the formulation. Complete separation of these preservatives was achieved on the same type of column as artemether using as eluent acetonitrile: potassium phosphate buffer pH 5.0 (0.05 M) (30:70, v/v). Quantitation was achieved with UV detection at 215 nm for artemether and 254 nm for the parabens, respectively. And in both methods, pump flow rate was 1.0 ml/min, sample injection volume 20 microl, ambient temperature maintained and no prior sample extraction methods were necessary throughout the experiments. Calibration curves were linear at concentration ranges of 4-16 microg/ml, 1-4 microg/ml and 1-10 mg/ml for methylparaben, propylparaben and artemether respectively. The excipient powder interference could be eliminated by diluting the sample and the analytes eluted at relatively short times using these systems. Both methods were further validated in terms of specificity, linearity, precision and accuracy. The procedures prescribed here are simple, selective and can be used for routine quality control and stability indicating tests involving the analysed compounds formulated in complex matrices.

Determination of the antimalaria drug artemether in pharmaceutical preparations by differential pulse polarography

A differential pulse polarographic method has been developed for the determination of artemether in its pharmaceutical formulations. The polarographic behaviour of artemether was examined in various buffer systems over the pH range 3.0-10.0. In phosphate buffer pH 5.5/methanol solution (7:3, v/v) the differential pulse polarograms displayed reproducible peaks at Ep-0.01 V versus Ag/AgCl. Under these conditions strict linearity between artemether concentration and peak height was observed in 3.4x10(-7)-3.0x10(-5)mol/L concentration range (R=0.9998). The detection limit was calculated to be 32 ng/mL. The polarographic method was applied to the determination of the content of artemether in tablets and capsules by using the standard addition method. The analysis of tablets containing 20mg artemether showed a mean value of 19.73 mg with a relative standard deviation (R.S.D.) of +/-1.01%. A content of 39.74 mg artemether was found in 40 mg capsules with a relative standard deviation of +/-0.53%. The polarographic method is characterised to be cheap, precise and not time-consuming and can therefore be used for routine analysis of artemether in its pharmaceutical preparations.

A high-performance liquid chromatography/tandem mass spectrometry method for the determination of artemisinin in rat plasma

Artemisinin is a widely used antimalarial drug. To evaluate the pharmacokinetics of artemisinin in rats, a sensitive and specific liquid chromatography/tandem mass spectrometric (LC/MS/MS) method was developed and validated for the determination of artemisinin in rat plasma. For detection, a Sciex API 4000 LC/MS/MS instrument with an electrospray ionization (ESI) TurboIonSpray inlet in the positive ion multiple reaction monitoring (MRM) mode was used to monitor precursor ([M+NH4]+) --> product ions of m/z 300.4 --> 209.4 for artemisinin and m/z 316.4 --> 163.4 for artemether, the internal standard (IS). The plasma samples were pretreated by a simple liquid-liquid extraction with ether. The standard curve was linear (r > 0.99) over the artemisinin concentration range of 1.0-200.0 ng/mL in plasma. The method had a lower limit of quantification of 1.0 ng/mL for artemisinin in 100 microL of plasma, which offered a satisfactory sensitivity for the determination of artemisinin. The intra- and inter-day precisions were measured to be within +/-5.3% and accuracy between -2.6% and 1.2% for all quality control samples, lower limit of quantification and upper limit of quantification samples. The extraction recoveries of artemisinin and the IS were 95.4 +/- 4.5% and 92.8 +/- 3.9%, respectively. This present method was successfully applied to the characterization of the pharmacokinetic profile of artemisinin in rats after oral administration.

Plasmodium falciparum-based bioassay for measurement of artemisinin derivatives in plasma or serum

Artemisinin and its derivatives, artesunate and artemether, are rapidly acting antimalarials that are used for the treatment of severe and uncomplicated multidrug-resistant falciparum malaria. To optimize treatment regimens that use this new class of antimalarials, there is a need for readily available and reproducible assays to monitor drug levels closely in patients. A sensitive and reproducible bioassay for the measurement of the concentrations of artemisinin derivatives in plasma and serum is described. By modifying the in vitro drug susceptibility test, it was found that antimalarial activity in plasma or serum containing an unknown concentration of drug could be equated to the known concentrations of dihydroartemisinin (DHA) required to inhibit parasite growth. Dose-response curves for a Plasmodium falciparum clone (clone W2) and DHA were used as a standard for each assay. Assays with plasma or serum spiked with DHA proved to be reproducible (coefficient of variation, <or=10.9%), with a lower limit of quantitation equivalent to 2.5 ng of DHA per ml. For plasma spiked with artesunate or artemether, there was good agreement of the results obtained by the bioassay and the concentrations measured by high-performance liquid chromatography (HPLC) with electrochemical detection. The bioassay for measurement of the antimalarial activities of artemisinin derivatives in body fluids requires a smaller volume of plasma or serum and is more sensitive than the presently available HPLC methods, can provide pharmacodynamic parameters for determination of activity against the parasite, and should enhance the design of more appropriate dosage regimens for artemisinin drugs.

Comparison of bioassay and high performance liquid chromatographic assay of artesunate and dihydroartemisinin in plasma

The study was a comparison of bioassay and HPLC analysis of artesunate (ARTS) and dihydroartemisinin (DHA) in plasma. ARTS and DHA in plasma samples from patients treated with ARTS were quantified by HPLC and expressed as DHA. DHA-equivalents in the same plasma samples were measured using a standardised parasite culture technique. DHA concentrations estimated by both methods were highly correlated (bioassay=0.96 x HPLC+11.0; r2=0.92). At high concentrations (>12000 nmol/l) bioassay sometimes overestimated DHA. Bioassay of active drug in plasma correlates well with specific chemical analysis by HPLC. ARTS and DHA appear to account for the total antimalarial activity in plasma after ARTS administration.

Preparation of beta-artemether liposomes, their HPLC-UV evaluation and relevance for clearing recrudescent parasitaemia in Plasmodium chabaudi malaria-infected mice

Egg phosphatidylcholine-cholesterol liposome formulations containing the antimalarial drug beta-artemether have been prepared and analyzed for their encapsulating capacity, chemical stability, leakage, in vitro release and their therapeutic efficiency against Plasmodium chabaudi infection. A HPLC-UV analysis of beta-artemether liposomes without derivatisation was achieved. A good linearity of y=4437.7 x+469.01 (R(2)=0.9999) with a detection limit of 2 microg ml(-1) was reached. Prior to this, liposomal formulations composed of different molar ratios of EPC-CHOL were prepared to select beta-artemether crystal-free liposome preparations. The formulation corresponding to 4:3 and a total concentration of 300 mg lipids ml(-1) buffer (pH 7.2), which could incorporate as much as 1.5 mg beta-artemether was selected for therapy. A trapping efficiency of nearly 100% was reached, the drug being located in the lipid bilayers. A dialysis test demonstrated that the drug could be reversibly released from the liposomes, reaching equilibrium within 24 h. After 3 months storage at 4 degrees C, no leakage of beta-artemether had occurred indicating a high stability of the liposomes. These liposomes were used to treat mice infected with the virulent rodent malaria parasite Plasmodium chabaudi chabaudi, with a 100% cure by clearing the recrudescent parasitaemia.

Pharmacokinetics of artemisinin-type compounds

Various compounds of the artemisinin family are currently used for the treatment of patients with malaria worldwide. They are characterised by a short half-life and feature the most rapidly acting antimalarial drugs to date. They are increasingly being used, often in combination with other drugs, although our knowledge of their main pharmacological features (including their absorption, distribution, metabolism and excretion) is still incomplete. Such data are particularly important in the case of combinations. Artemisinin derivatives are converted primarily, but to different extents, to the bioactive metabolite artenimol after either parenteral or gastrointestinal administration. The rate of conversion is lowest for artelinic acid (designed to protect the molecule against metabolism) and highest for the water-soluble artesunate. The absolute and relative bioavailability of these compounds has been established in animals, but not in humans, with the exception of artesunate. Oral bioavailability in animals ranges, approximately, between 19 and 35%. A first-pass effect is highly probably for all compounds when administered orally. Artemisinin compounds bind selectively to malaria-infected erythrocytes to yet unidentified targets. They also bind modestly to human plasma proteins, ranging from 43% for artenimol to 81.5% for artelinic acid. Their mode of action is still not completely understood, although different theories have been proposed. The lipid-soluble artemether and artemotil are released slowly when administered intramuscularly because of the 'depot' effect related to the oil formulation. Understanding the pharmacokinetic profile of these 2 drugs helps us to explain the characteristics of the toxicity and neurotoxicity. The water-soluble artesunate is rapidly converted to artenimol at rates that vary with the route of administration, but the processes need to be characterised further, including the relative contribution of pH and enzymes in tissues, blood and liver. This paper intends to summarise contemporary knowledge of the pharmacokinetics of this class of compounds and highlight areas that need further research.

Artemisinin drugs: novel antimalarial agents

Artemisinin and its derivatives, artesunate and artemether, represent a new class of antimicrobial drug with potent activity against Plasmodium falciparum. Although they show excellent efficacy in both severe and uncomplicated malaria, dosage regimens still need to be optimised and pharmacokinetic profiles defined. In the treatment of uncomplicated malaria, the artemisinin drugs should be used in combination with a long acting antimalarial to protect both drugs against the emergence of resistance. In the treatment of severe malaria, parenteral artemether is at least as effective as quinine and is simpler to use. The use of rectal preparations of artesunate and artemisinin at the rural health level will facilitate early initiation of the treatment of falciparum malaria and this may reduce the proportion of patients progressing to severe disease. All of the artemisinin drugs have comparable efficacy; the choice of derivative should be based upon availability, cost and quality of the preparation. Artemisinin, artesunate and artemether are well-tolerated in both adults and children, with no evidence to date of serious clinical toxicity.

Direct analysis of artemisinin in plasma and saliva using coupled-column high-performance liquid chromatography with a restricted-access material pre-column

A previously established HPLC system with post-column derivatization for the analysis of artemisinin was coupled to an ADS (alkyl-diol silica) pre-column, allowing direct and repetitive injection of protein-rich fluids such as plasma. The limit of quantitation for 100 microl of plasma was 10 ng/ml (CV=10.5%) while concentrations down to 2 ng/ml could be quantified for 1.00 ml saliva samples (CV=11.1%). The system was linear in the tested range of 10-2000 ng/ml for plasma and 2-240 ng/ml for saliva samples, respectively. This paper introduces coupled column HPLC as a simplified method for the routine analysis of artemisinin in biological fluids.

Pharmacokinetic interaction trial between co-artemether and mefloquine

Forty-two healthy subjects were randomized in a parallel three-group design trial to investigate potential electrocardiographic and pharmacokinetic interactions between the new antimalarial co-artemether, a combination of artemether and lumefantrine (both of which are predominantly metabolized through CYP3A4), and mefloquine, another antimalarial described as a substrate (and possible inhibitor) of CYP3A4. Subjects were assigned to one of the three possible treatment groups (i.e., co-artemether alone or mefloquine alone or the combination of both). The dosage was 1000 mg mefloquine (divided into three doses over 12 h) followed 12 h later by six applications of co-artemether (40 mg artemether+480 mg lumefantrine each) over 60 h. The study medications were generally well tolerated after all treatments. Concomitant administration with mefloquine caused statistically significant lower (around 30-40%) plasma concentrations of lumefantrine than when co-artemether was administered alone. Even if important, this decrease in lumefantrine exposure was considered unlikely to impact clinical efficacy given the wide therapeutic index of co-artemether and the usual high variability in lumefantrine plasma levels, mostly and more importantly influenced by food intake. However, patients should be encouraged to eat at dosing times to compensate for this decreased bioavailability. The pharmacokinetics of artemether, DHA or mefloquine were not affected. Artemether concentrations significantly decreased over doses, independently of mefloquine co-administration, while DHA concentrations slightly (not significantly) increased. Therefore, no clinically relevant risks due to pharmacokinetic drug-drug interaction are expected at the enzymatic level following co-administration of co-artemether with CYP3A4 substrates with similar affinity to that of mefloquine.

Clinical pharmacokinetics and pharmacodynamics and pharmacodynamics of artemether-lumefantrine

The combination of artemether and lumefantrine (benflumetol) is a new and very well tolerated oral antimalarial drug effective even against multidrug-resistant falciparum malaria. The artemether component is absorbed rapidly and biotransformed to dihydroartemisinin, and both are eliminated with terminal half-lives of around 1 hour. These are very active antimalarials which give a rapid reduction in parasite biomass and consequent rapid resolution of symptoms. The lumefantrine component is absorbed variably in malaria, and is eliminated more slowly (half-life of 3 to 6 days). Absorption is very dependent on coadministration with fat, and so improves markedly with recovery from malaria. Thus artemether clears most of the infection, and the lumefantrine concentrations that remain at the end of the 3- to 5-day treatment course are responsible for eliminating the residual 100 to 10 000 parasites. The area under the curve of plasma lumefantrine concentrations versus time, or its correlate the plasma concentration on day 7. has proved an important determinant of therapeutic response. Characterisation of these pharmacokinetic-pharmacodynamic relationships provided the basis for dosage optimisation, an approach that could be applied to other antimalarial drugs.

Rapid determination of artemisinin and related analogues using high-performance liquid chromatography and an evaporative light scattering detector

Artemisinin and its analogues are a class of compounds of current interest in the treatment of drug-resistant malaria. These antimalarials are preferentially taken up into malaria infected erythrocytes as compared to uninfected erythrocytes, a fact that may represent an important parameter in drug potency. Numerous methods for the analysis of specific artemisinin analogues have been developed, but most are not widely adaptable to a large range of analogues. In this paper we describe a high-performance liquid chromatographic method developed and validated for artemisinin and several analogues of artemisinin using a readily available evaporative light scattering detector. This quantitation method was found to be straight forward, rapid, inexpensive and reproducible. Standard calibration curves constructed for six artemisinin compounds were linear with the detection limit determined between 6 and 60 ng. The intra- and inter-day accuracy were found to be 2.75% and 4.15%, respectively with less than 3% variation in precision. The validated assay was applied to a mixture of artemisinin derivatives, where they were easily separated and quantitated.

Effects of alpha-thalassemia on pharmacokinetics of the antimalarial agent artesunate

Thalassemia is common in Southeast Asia, where artemisinin derivatives are frequently used in the treatment of malaria. It has been previously reported that artemisinin derivatives can be concentrated by uninfected thalassemic erythrocytes in vitro but not by normal erythrocytes. As a follow-up to this report, we studied the antimalarial kinetics of intravascular artesunate (2.4 mg/kg of body weight) in 10 persons with normal hemoglobins and in 10 patients with thalassemia (2 with alpha-thalassemia type 1-hemoglobin Constant Spring and 8 with alpha-thalassemia type 1-alpha-thalassemia type 2). Concentrations of artesunate and its active metabolites in plasma were measured by bioassay and expressed relative to those of dihydroartemisinin, the major biologically active metabolite. Concentrations of intravascular artesunate in plasma peaked in both the normal individuals and the thalassemic individuals 15 min after injection (the first time point). Plasma drug concentrations at all time intervals, except that at 1 h, were significantly higher in thalassemic subjects than in normal subjects (P < 0.05). The area under the concentration-time curve was 9-fold higher (P < 0.001) and the volume of distribution at steady state was 15-fold lower (P < 0.001) in thalassemic than in normal subjects. In light of the potential neurotoxicity of artemisinin derivatives, these results suggest that thalassemic subjects may need a drug administration regimen different from that of normal patients.

Simple high-performance liquid chromatographic method with electrochemical detection for the simultaneous determination of artesunate and dihydroartemisinin in biological fluids

A simple, rapid, sensitive, selective and reproducible high-performance liquid chromatographic method with reductive electrochemical detection is described for the simultaneous quantification of artesunate (ARS) and dihydroartemisinin (DHA) in plasma. The procedure involved the extraction of ARS, DHA and the internal standard (artemisinin, ARN) with a mixture of dichloromethane and tert.-methyl butyl ether (8:2, v/v). Chromatographic separation consisted of the mobile phase (acetonitrile-water containing 0.1 M acetic acid, pH 4.8; 45:55, v/v) running through the column (Nova-Pak C18, 150 cm x 3.9 mm I.D., 5 microm particle size). The retention times of alpha-DHA, beta-DHA, ARS and ARN were 2.9, 4.2, 4.5 and 6.0 min, respectively. The average recoveries of ARS, alpha-DHA and ARN in the concentration range of 10-800 ng/ml were 81.9, 88.2, 101.1 and 84.3%, respectively. The coefficients of variation (precision and repeatability) were below 10% for all three compounds at concentrations of 50, 200, 400 and 800 ng/ml, and below 20% at a concentration of 10 ng/ml. The limits of quantification for both ARS and alpha-DHA in spiked plasma samples were 5 and 3 ng/ml, respectively. The method was found to be suitable for application to pharmacokinetic studies of both ARS and DHA.

Validation of an improved reversed-phase high-performance liquid chromatography assay with reductive electrochemical detection for the determination of artemisinin derivatives in man

For the determination of artemisinin (ART) and analogs, a reversed-phase high-performance liquid chromatography method using reductive electrochemical detection (ED) was set up with some important modifications as compared to previously published assays. A different technique of deoxygenating resulted in a factor 2-3 lower background current. A Spectroflow 400 liquid chromatograph in combination with a Triathlon autoinjector coupled to a Decade electrochemical detector was used. The detector was operated in the reductive mode as a closed system under chromatography grade helium to exclude any access of oxygen. The Decade has a glassy carbon electrode and a reference Ag/AgCl electrode. Infrequent electropolishing was required implicating a very stable system. By increasing acetonitril or lowering the pH of the mobile phase, the various derivatives could be determined in the same chromatogram. The assay was validated using artemether (ATM) and dihydroartemisinin (DHA) as test substances. In the concentration range seen in people after usual doses (5 to 220 ng/ml), the assay performs with adequate accuracy and precision. The interassay and intraassay precision are < 6% for ATM. For DHA, the interassay and intraassay precision are < 9%. The accuracy expressed as the deviation from the expected concentration varies from -1% to +4.5% for the intraassay ATM-determinations and from +1% to +6.3% for the interassay measurements. For DHA, the accuracy is somewhat less, varying from -0.3% to -9.5% for the intraassay measurements and -0.6% to +2.6% for the interassay measurements. The reproducibility of the assay, measured over a time period of 3 months, is good for ATM and DHA with an interassay precision of < 18% in 70 repetitive samples and an accuracy varying from -0.6% to +7.6%. In a cross-check with two other reference laboratories who used comparable methods of determination, a strong correlation (correlation coefficient > 0.98) was achieved. The method was applied in a study in which artemether was administered orally to healthy white subjects. We consider high-performance liquid chromatography with electrochemical detection an accurate and precise method for quantitative determination of artemisinin derivatives in pharmacokinetic studies.

Determination of artemether and its metabolite, dihydroartemisinin, in plasma by high-performance liquid chromatography and electrochemical detection in the reductive mode

An analytical method for the determination of artemether (A) and its metabolite dihydroartemisinin (DHA) in human plasma has been developed and validated. The method is based on high-performance liquid chromatography (HPLC) and electrochemical detection in the reductive mode. A, DHA and artemisinin, the internal standard (I.S.), were extracted from plasma (1 ml) with 1-chlorobutane-isooctane (55:45, v/v). The solvent was transferred, evaporated to dryness under nitrogen and the residue dissolved in 600 microliters of water-ethyl alcohol (50:50, v/v). Chromatography was performed on a Nova-Pak CN, 4 microns analytical column (150 mm x 3.9 mm I.D.) at 35 degrees C. The mobile phase consisted of pH 5 acetate-acetonitrile (85:15, v/v) at a flow-rate of 1 ml/min. The analytes were detected by electrochemical detection in the reductive mode at a potential of -1.0 V. Intra-day accuracy and precision were assessed from the relative recoveries (found concentration in % of the nominal value) of spiked samples analysed on the same day (concentration range 10.9 to 202 ng/ml of A and 11.2 to 206 ng/ml of DHA in plasma). The mean recoveries over the entire concentration range were from 96 to 100% for A with C.V. from 6 to 13%, from 92% to 100% for DHA (alpha-tautomer) with C.V. from 4 to 16%. For A, the mean recovery was 96% at the limit of quantitation (LOQ) of 10.9 ng/ml with a C.V. of 13%. For DHA, the mean recovery was 100% at the LOQ of 11.2 ng/ml with a C.V. of 16%.

Determination of artemether and its major metabolite, dihydroartemisinin, in plasma using high-performance liquid chromatography with electrochemical detection

A rapid, selective, sensitive and reproducible HPLC with reductive electrochemical detection for quantitative determination of artemether (ART) and its plasma metabolite, dihydroartemisinin (DHA: alpha and beta isomers) in plasma is described. The procedure involved the extraction of ART, DHA and the internal standard, artemisinin (ARN) with dichloromethane-tert.-methylbutyl ether (1:1, v/v) or n-butyl chloride-ethyl acetate (9:1, v/v). Chromatographic separation was performed with a mobile phase of acetonitrile-water (20:80, v/v) containing 0.1 M acetic acid pH 5.0, running through a microBondapak CN column. The method was capable of separating the two isomeric forms of DHA (alpha, beta). The retention times of alpha-DHA, beta-DHA, ARN and ART were 4.6, 5.9, 7.9 and 9.6 min, respectively. Validation of the assay method was performed using both extraction systems. The two extraction systems produced comparable recoveries of the various analytes. The average recoveries of ART, DHA and ARN over the concentration range 80-640 ng/ml were 86-93%. The coefficients of variation were below 10% for all three drugs (ART, alpha-DHA, ARN). The minimum detectable concentrations for ART and alpha-DHA in spiked plasma samples were 5 and 3 ng/ml, respectively. The method was found to be suitable for use in clinical pharmacokinetic study.

Artemisinin and the antimalarial endoperoxides: from herbal remedy to targeted chemotherapy

Artemisinin and its derivatives are endoperoxide-containing compounds which represent a promising new class of antimalarial drugs. In the presence of intraparasitic iron, these drugs are converted into free radicals and other electrophilic intermediates which then alkylate specific malaria target proteins. Combinations of available derivatives and other antimalarial agents show promise both as first-line agents and in the treatment of severe disease.