High-performance liquid chromatographic determination of quinine in plasma, whole blood and samples dried on filter paper

Research progress in electroanalytical techniques for determination of antimalarial drugs in pharmaceutical and biological samples

The review focusses on the role of electroanalytical methods for determination of antimalarial drugs in biological matrices and pharmaceutical formulations with a critical analysis of published voltammetric and potentiometric methods.

World Antimalarial Resistance Network (WARN) IV: clinical pharmacology

A World Antimalarial Resistance Network (WARN) database has the potential to improve the treatment of malaria, through informing current drug selection and use and providing a prompt warning of when treatment policies need changing. This manuscript outlines the contribution and structure of the clinical pharmacology component of this database. The determinants of treatment response are multi-factorial, but clearly providing adequate blood concentrations is pivotal to curing malaria. The ability of available antimalarial pharmacokinetic data to inform optimal dosing is constrained by the small number of patients studied, with even fewer (if any) studies conducted in the most vulnerable populations. There are even less data relating blood concentration data to the therapeutic response (pharmacodynamics). By pooling all available pharmacokinetic data, while paying careful attention to the analytical methodologies used, the limitations of small (and thus underpowered) individual studies may be overcome and factors that contribute to inter-individual variability in pharmacokinetic parameters defined. Key variables for pharmacokinetic studies are defined in terms of patient (or study subject) characteristics, the formulation and route of administration of the antimalarial studied, the sampling and assay methodology, and the approach taken to data analysis. Better defining these information needs and criteria of acceptability of pharmacokinetic-pharmacodynamic (PK-PD) studies should contribute to improving the quantity, relevance and quality of these studies. A better understanding of the pharmacokinetic properties of antimalarials and a more clear definition of what constitutes "therapeutic drug levels" would allow more precise use of the term "antimalarial resistance", as it would indicate when treatment failure is not caused by intrinsic parasite resistance but is instead the result of inadequate drug levels. The clinical pharmacology component of the WARN database can play a pivotal role in monitoring accurately for true antimalarial drug resistance and promptly correcting sub-optimal dosage regimens to prevent these contributing to the emergence and spread of antimalarial resistance.

High-performance liquid chromatographic method for the determination of quinine and 3-hydroxyquinine in blood samples dried on filter paper

A simple high-performance liquid chromatographic method for the simultaneous analysis of quinine and 3-hydroxyquinine in blood samples dried on filter paper is described. Sample preparation involves liquid-liquid extraction with toluene-butanol 75:25 (v/v) followed by evaporation. A reversed-phase liquid chromatography system with fluorescence detection was used. The limit of determination was 10 nM for both quinine and 3-hydroxyquinine and the recovery varied between 78 and 109%. The within- and between-assay coefficients of variation varied between 2-5% and 4-10%, respectively. No loss of either analyte occurred after storage for 2 months at room temperature or at 37 degrees C. This method for sampling has advantages that make it of great value for clinical and pharmacokinetic studies especially in remote regions where storage and transportation is problematic.

Improved RP-HPLC determination of quinine in plasma and whole blood stored on filter paper

Analysis of quinine in plasma and whole blood samples dried on filter paper is described. Sample preparation involves liquid extraction of plasma and whole blood from the filter paper and subsequent solid-phase extraction using C8 Bond Elut cartridges. A reverse-phase liquid chromatography system with UV detection and fluorescence detection was used. The analytical characteristics of the method are reported, with a quantification limit of 0.1 microg mL(-1) and within an assay coefficient of variation of 5.6-8.4% in plasma and 6.5-12% in whole blood. Representative chromatograms are shown as a function of time for samples from human subjects after ingestion of a single 400-mg dose of quinine sulphate. Quinidine, dihydroquinine and metabolites are well separated from quinine with a resolution of above 1 (Rs>1).

Improved method for the simultaneous determination of proguanil and its metabolites by high-performance liquid chromatography and solid-phase extraction of 100-microl capillary blood samples dried on sampling paper

An improved method is presented for the determination of proguanil, cycloguanil and 4-chlorophenylbiguanide in 100-microl capillary blood samples applied to sampling paper. This method also utilises a solid-phase extraction technique and high-performance liquid chromatography. Different kinds of sampling paper, such as ion-exchange and cellulose sampling paper were tested. The best elution recovery (70-80%) was obtained after treatment of cellulose sampling paper with a quaternary ammonium compound. The limit of determination was 50 nmol/l for cycloguanil and 4-chlorophenylbiguanide and 125 nmol/l for proguanil using 100 microl capillary blood. The stability of the analytes and elution performance from sampling paper was validated at different temperature and storage time. Venous blood and capillary blood concentrations of proguanil and metabolites were found to be similar.

Determination of proguanil and metabolites in small sample volumes of whole blood stored on filter paper by high-performance liquid chromatography

A method is reported for the determination of proguanil and its two metabolites cycloguanil and 4-chlorophenylbiguanide in whole blood and plasma samples obtained by thumbprick and stored dry on filter paper. The sample preparation involves liquid extraction from the filter paper and subsequent solid-phase extraction using C8 Bond-Elut cartridges. Separation and quantification is by a previously reported ion-pairing high-performance liquid chromatographic system with ODS Hypersil as stationary phase and an 50:50 acetonitrile-pH 2 phosphate buffer mobile phase containing 200 mM sodium dodecylsulphate as ion-pairing agent. The analytical characteristics of the method are reported. Representative concentrations are shown as a function of time from a human subject after ingestion of a single 200-mg dose of proguanil hydrochloride. Typical ranges of concentration detected by the proposed method in human subjects were proguanil 12-900 ng/ml, cycloguanil 16-44 ng/ml and 4-chlorophenylbiguanide 1.5-10 ng/ml in whole blood.

Column liquid chromatographic analysis of quinine in human plasma, saliva and urine

A new simple, selective and reproducible high-performance liquid chromatographic method for the determination of quinine in plasma, saliva and urine is described. The ion-pair method was carried out on a reversed-phase C18 column, using perchlorate ion as the counter ion and ultraviolet detection at 254 nm. Quinine was well resolved from its major metabolite, 3-hydroxyquinine, and the internal standard, primaquine. The limit of detection was 10 ng/ml and the recovery was greater than 90% from the three biological fluids.

High-performance liquid chromatographic method for the simultaneous determination of mefloquine and its carboxylic metabolite in 100-microliters capillary blood samples dried on paper

A reversed-phase high-performance liquid chromatographic method is described for the analysis of mefloquine and its carboxylic metabolite in 100-microliters capillary blood spots dried on chromatographic paper. Each spot was cut into small pieces, and mefloquine and its metabolite were eluted with an ammonia-water solution (10:90, v/v). The compounds were extracted simultaneously after alkalization at pH 9.5 using tetrabutylammonium as ion-pairing agent and then separated on a C18 column with ultraviolet detection at 227 nm. The recovery of the drugs from spiked blood applied to paper and dried was 70-80%, and the inter-assay precision at 1.0-5.0 mumol/l (therapeutic range) was less than 10%. The correlation between extractions from venous whole blood and capillary blood applied to chromatographic paper was more than 0.94. The analytes were stable in dried blood spots for at least fifty days at -20 degrees C. The decrease of concentration was less than 10%, when the paper was stored at 37 degrees C for fifty days. The assay is reliable and easy to use for therapeutic monitoring of mefloquine with a lower limit of determination of 0.3-0.5 mumol/l.

Determination of quinine in serum, plasma, red blood cells and whole blood in healthy and Plasmodium falciparum malaria cases by high-performance liquid chromatography

A normal-phase high-performance liquid chromatographic method using dichloromethane-methanol-1 M perchloric acid (100:9:0.4, v/v) at a flow-rate of 0.8 ml/min on a Zorbax-Sil column with fluorescence detection has been developed for the separation of quinine and quinidine from other antimalarials. Within-day and day-to-day coefficients of variation averaged 0.74 and 7.56%, respectively. The extraction recovery of quinine for plasma, serum, red blood cells and whole blood (filter paper) was 88.13, 87.12, 78.0 and 77.5%, respectively. The method is capable of separating quinine from dihydroquinine, a compound usually found as an impurity in authentic quinine samples. The method has been used for the determination of quinine in plasma, serum, red blood cells and whole blood (filter paper) of six healthy and twenty Plasmodium falciparum malaria cases. The average quinine concentration in P. falciparum malaria cases was three to four times higher than that in healthy volunteers. Quinine was absorbed much less in red blood cells than in plasma or serum.

Simultaneous determination of chloroquine and quinine in human biological fluids by high-performance liquid chromatography

A high-performance liquid chromatographic method with fluorescence detection is described for the simultaneous measurement of quinine, chloroquine and mono- and bidesethylchloroquine in human plasma, erythrocytes and urine. After a liquid-solid extraction on a Bond Elut C8 cartridge, the compounds are separated on an Inertsil silica column by gradient elution; the mobile phase is a mixture of acetonitrile and methanol-25% ammonia solution (92.7:7.5, v/v). The eluent was monitored with a fluorescence detector (excitation wavelength 325 nm and emission wavelength 375 nm). The limit of detection was ca. 5 ng/ml for chloroquine and ca. 23 ng/ml for quinine. No chromatographic interferences could be detected from endogenous compounds or other antimalarial drugs. The method is accurate with inter- and intra-assay coefficients of variation lower than 7%. Hydroxychloroquine is used as an internal standard because of its structural similarity to chloroquine. The procedure requires 30 min and can be used for therapeutic drug monitoring.

Hearing impairment related to plasma quinine concentration in healthy volunteers

1. Hearing impairment was investigated in six healthy volunteers who received oral doses of 5, 10 and 15 mg kg-1 quinine single-blind and in random order. 2. The plasma concentration of quinine was followed for 48 h and the time course was fitted by a linear one compartment pharmacokinetic model. 3. Hearing thresholds were measured by pure tone audiometry. There was a delay between impairment in hearing and change in plasma quinine concentration. Thus the method of effect compartment modelling was applied. 4. The effect on hearing (L), measured as a shift in hearing threshold (dB), was used to estimate the rate constant for elimination of drug from the assumed effect compartment (ke0) and two parameters specifying the effect model (gamma and k). The effect model applied was L = 10 (log k + gamma x log Ce) where Ce is the calculated drug concentration in the effect compartment. This model is a logarithmic transform of a power expression equivalent to the Hill equation at the lower end of the effect range. In all experiments where there was a clear effect on hearing, convergence on a set of parameter estimates occurred, but inter- and intraindividual variability was large. The mean value of ke0 was 3.32 +/- 5.93 h-1 s.d., for gamma it was 1.73 +/- 1.14 s.d. and for k it was 0.59 +/- 0.66 s.d.

The effect of quinine on psychoacoustic tuning curves, stapedius reflexes and evoked otoacoustic emissions in healthy volunteers

Quinine causes reversible hearing loss, closely related to the quinine plasma concentration. The effects of quinine on psychoacoustic tuning curves, stapedius reflex thresholds and evoked otoacoustic emissions were studied in healthy volunteers. The tuning curves became shallower, whereas reflex thresholds were unaffected. The shift in the emission thresholds paralleled that of the pure-tone thresholds. There were also qualitative changes in the emissions: 1) the exponent of the stimulus-response function changed from 0.34 to 0.56; 2) decay time shortened; 3) the power spectrum shifted towards lower frequencies. The results are discussed in relation to various aspects of cochlear performance and are suggested to depend on an outer hair cell dysfunction.

Audiometry as a possible indicator of quinine plasma concentration during treatment of malaria

The spread of chloroquine-resistant malaria has led to a resurgence of quinine in clinical use. One of the well-known side effects of quinine, reversible hearing loss, is closely related to the plasma concentration. We suggest that this hearing effect could be used as an aid in therapy control when quinine drug assay is not available.