Quinine levels revisited: the value of routine drug level monitoring for those on parenteral therapy

Revisiting the Effect of Pharmaceuticals on Transmission Stage Formation in the Malaria Parasite Plasmodium falciparum

Malaria parasites rely on specialized stages, called gametocytes, to ensure human-to-human transmission. The formation of these sexual precursor cells is initiated by commitment of blood stage parasites to the sexual differentiation pathway. Plasmodium falciparum, the most virulent of six parasite species infecting humans, employs nutrient sensing to control the rate at which sexual commitment is initiated, and the presence of stress-inducing factors, including antimalarial drugs, has been linked to increased gametocyte production in vitro and in vivo. These observations suggest that therapeutic interventions may promote gametocytogenesis and malaria transmission. Here, we engineered a P. falciparum reporter line to quantify sexual commitment rates after exposure to antimalarials and other pharmaceuticals commonly prescribed in malaria-endemic regions. Our data reveal that some of the tested drugs indeed have the capacity to elevate sexual commitment rates in vitro. Importantly, however, these effects are only observed at drug concentrations that inhibit parasite survival and only rarely result in a net increase of gametocyte production. Using a drug-resistant parasite reporter line, we further show that the gametocytogenesis-promoting effect of drugs is linked to general stress responses rather than to compound-specific activities. Altogether, we did not observe evidence for mechanistic links between the regulation of sexual commitment and the activity of commonly used pharmaceuticals in vitro. Our data hence does not support scenarios in which currently applied therapeutic interventions would promote the spread of drug-resistant parasites or malaria transmission in general.

Updated pharmacokinetic considerations for the use of antimalarial drugs in pregnant women

INTRODUCTION

The association between pregnancy and altered drug pharmacokinetic (PK) properties is acknowledged, as is its impact on drug plasma concentrations and thus therapeutic efficacy. However, there have been few robust PK studies of antimalarial use in pregnancy. Given that inadequate dosing for prevention or treatment of malaria in pregnancy can result in negative maternal/infant outcomes, along with the potential to select for parasite drug resistance, it is imperative that reliable pregnancy-specific dosing recommendations are established.

AREAS COVERED

PK studies of antimalarial drugs in pregnancy. The present review summarizes the efficacy and PK properties of WHO-recommended therapies used in pregnancy, with a focus on PK studies published since 2014.

EXPERT OPINION

Changes in antimalarial drug disposition in pregnancy are well described, yet pregnant women continue to receive treatment regimens optimized for non-pregnant adults. Contemporary in silico modeling has recently identified a series of alternative dosing regimens that are predicted to provide optimal therapeutic efficacy for pregnant women.

Effect of dehusked Garcinia kola seeds on the overall pharmacokinetics of quinine in healthy Nigerian volunteers

We investigated the effect of concurrent ingestion of Garcinia kola seed on the pharmacokinetics of quinine. In a randomized crossover study, 24 healthy Nigerian volunteers were assigned into 2 groups (A and B; n = 12 per group) on the basis of G. kola dose orally ingested. Each subject received 600 mg quinine sulfate before and after ingesting 12.5 g of G. kola once daily for 7 days (group A) or 12.5 g twice daily for 6 days and once on the seventh day (group B). Blood samples were collected and analyzed for plasma quinine and its metabolite (3-hydroxyquinine) using a validated high performance liquid chromatography method. Concurrent administration of quinine with G. kola reduced quinine tmax by 48% (group A), mean Cmax by 19% and 26% in groups A and B, respectively, and slight reduction in mean AUC0- ∞ of quinine in both groups. 3-hydroxyquinine Cmax also reduced by 29% and 32%; AUC0-∞ by 13% and 9%, respectively. The point estimates of the T/R ratio of the geometric means for all Cmax obtained and only the AUC0-∞ at a higher dose of G. kola were outside the 80%-125% bioequivalence range. In conclusion, an herb-drug interaction was noted with concurrent quinine and G. kola administration.

Relationship between plasma and red blood cell concentrations of quinine in Brazilian children with uncomplicated Plasmodium falciparum malaria on oral therapy

We determined the relationship between plasma and red blood cell concentrations of quinine in children with uncomplicated falciparum malaria from an endemic area of Amazonian region. Quinine was determined by high performance liquid chromatography with ultraviolet detection. In the steady state the ratio between plasma and red blood cell quinine concentration was 1.89 +/- 1.25 ranging from 1.05 to 2.34. This result demonstrated that quinine do not concentrate in red blood cell of Brazilian children and characterize the absence of interracial difference in this relationship.

Permeation of quinine across sublingual mucosa, in vitro

Quinine is the first line treatment in severe P. falciparum malaria and nocturnal leg cramps and a fast, convenient delivery method of this drug quinine is needed. The purpose of this study was to investigate in vitro the sublingual route for the delivery of quinine. Permeation studies were carried out with Franz diffusion cells containing sublingual mucosa membranes with PBS receptor phase and dosed with solutions of quinine hydrochloride or quinine/2-hydroxypropyl-beta-cyclodextrin complexes. Receptor phase samples were taken 2 hourly over a 12h period and quinine was determined by reverse-phase HPLC analysis. The ventral surface of the tongue was significantly more permeable than porcine floor of the mouth (p<0.05) and there was no significant effect of freezing on the ventral surface of the tongue (p 0.2444). The presence of saliva caused a decrease in the permeation of quinine across the ventral surface of the tongue by up to 68%. Inclusion complexation between quinine and 2-HP-beta-CD was supported by (1)H NMR spectral data, and an ethanol vehicle provided the highest quinine flux from the inclusion complex solutions compared to deionised water and PEG. Overall, the data support further investigations into the clinical use of sublingual quinine, particularly for children with falciparum malaria or patients with nocturnal leg cramps. Use of quinine/cyclodextrin inclusion complexes may circumvent compliance issues due to bitter taste.

Rapid gas chromatography/mass spectrometry quinine determination in plasma after automated solid-phase extraction

The combined use of an automatic solid-phase extraction (SPE) apparatus with Oasis MCX cartridges and gas chromatography/mass spectrometry (GC/MS) to rapidly quantify quinine in biological samples with cyproheptadine as the internal standard is described. The selected ion monitoring mode, with the quantification ions m/z 136 and 287 (qualifier ions: m/z 261, 381 and 215, 96), allows the estimation of quinine levels, respectively. Separation was completed within 12.7 min. Excellent linearity was found up to 10 000 microg/L of plasma. The limit of detection (LOD) was 12.2 microg/L and the limit of quantification (LOQ) was 40.6 microg/L. High reproducibility (intra-assay CV range 1.9-4.3%, inter-assay CV range 2.2-11.3%) and accuracy values (intra-assay range 83.2-103.7%, inter-assay range 86.8-103.7%) were obtained. Recoveries were concentration-independent (97.2% and 89.8% for 4000 and 10 000 microg/L, respectively). This sensitive, simple assay for quinine in various matrices meets the current requirements for bioanalytical assays and may be used to monitor quinine levels in patients developing severe malaria with acute renal failure during hemofiltration. The optimal quinine dose in this situation is not really established and to improve clinical care, quinine concentrations might be explored to improve efficacy and minimise potential toxicity.