Artesunate, artemether or quinine in severe Plasmodium falciparum malaria?

Antimalarial and anticancer properties of artesunate and other artemisinins: current development

This review provides a recent perspective of artesunate and other artemisinins as antimalarial drugs and their uses in cancer therapy. Artesunate is an artemisinin derivative. Artemisinin is extracted from the plant Artemisia annua. Artemisinin and its derivatives have been the most useful drug for malarial treatment in human history. The artesunate has an advantage of a hydrophilic group over other artemisinins which makes it a more potent drug. On the industrial scale, artemisinins are synthesized in semisynthetic ways. The 1,2,4-endoperoxide bridge of artemisinins is responsible for the drug's antimalarial activity. There is the emergence of artemisinin resistance on Plasmodium falciparum and pieces of evidence suggest that it is mainly due to the mutation at Kelch13 protein of P. falciparum. Clinical trial data show that the artesunate is more favorable than quinine and other artemisinins to treat patients with severe malaria. Pieces of evidence indicate that artemisinins can be developed as anticancer drugs. The mechanism of actions on how artemisinins act as an anticancer drug involves oxidative stress, DNA damage and repair, and various types of cell deaths.

GRAPHIC ABSTRACT

In vitro susceptibility of Indian Plasmodium falciparum isolates to different antimalarial drugs & antibiotics

Background & objectives:

The in vitro assays for susceptibility of Plasmodium falciparum to antimalarial drugs are important tools for monitoring drug resistance. During the present study, efforts were made to establish long-term continuous in vitro culture of Indian field isolates of P. falciparum and to determine their sensitivity to standard antimalarial drugs and antibiotics.

Methods:

Four (MZR-I, -II, -III and -IV) P. falciparum isolates were obtained from four patients who showed artemisinin-based combination therapy (ACT) from Mizoram, a north-eastern State of India, and characterized for their in vitro susceptibility to chloroquine diphosphate (CQ), quinine hydrochloride dehydrate, mefloquine, piperaquine, artemether, arteether, dihydro-artemisinin (DHA), lumefantrine and atovaquone and antibiotics, azithromycin and doxycycline. These patients showed ACT treatment failure. Two-fold serial dilutions of each drug were tested and the effect was evaluated using the malaria SYBR Green I fluorescence assay. K1 (chloroquine-resistant) and 3D7 (chloroquine-sensitive) reference strains were used as controls.

Results:

Growth profile of all field isolates was identical to that of reference parasites. The IC₅₀ values of all the drugs were also similar against field isolates and reference parasite strains, except K1, exhibited high IC₅₀ value (275±12.5 nM) of CQ for which it was resistant. All field isolates exhibited higher IC₅₀ values of CQ, quinine hydrochloride dihydrate and DHA compared to reference strains. The resistance index of field isolates with respect to 3D7 ranged between 260.55 and 403.78 to CQ, 39.83 and 46.42 to quinine, and 2.98 and 4.16 to DHA, and with respect to K1 strain ranged between 6.51 and 10.08, 39.26 and 45.75, and 2.65 and 3.71. MZR-I isolate exhibited highest resistance index.

Interpretation & conclusions:

As the increase in IC₅₀ and IC₉₀ values of DHA against field isolates of P. falciparum was not significant, the tolerance to DHA-piperaquine (PPQ) combination might be because of PPQ only. Further study is required on more number of such isolates to generate data for a meaningful conclusion.

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

The present review describes the current status of synthetic five and six-membered cyclic peroxides such as 1,2-dioxolanes, 1,2,4-trioxolanes (ozonides), 1,2-dioxanes, 1,2-dioxenes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes. The literature from 2000 onwards is surveyed to provide an update on synthesis of cyclic peroxides. The indicated period of time is, on the whole, characterized by the development of new efficient and scale-up methods for the preparation of these cyclic compounds. It was shown that cyclic peroxides remain unchanged throughout the course of a wide range of fundamental organic reactions. Due to these properties, the molecular structures can be greatly modified to give peroxide ring-retaining products. The chemistry of cyclic peroxides has attracted considerable attention, because these compounds are used in medicine for the design of antimalarial, antihelminthic, and antitumor agents.

Pharmacodynamics of antimalarial chemotherapy

Malaria chemotherapy is under constant threat from the emergence and spread of multidrug resistance of Plasmodium falciparum. Resistance has been observed to almost all currently used antimalarials. Some drugs are also limited by toxicity. A fundamental component of the strategy for malaria chemotherapy is based on prompt, effective and safe antimalarial drugs. To counter the threat of resistance of P. falciparum to existing monotherapeutic regimens, current malaria treatment is based principally on the artemisinin group of compounds, either as monotherapy or artemisinin-based combination therapies for treatment of both uncomplicated and severe falciparum malaria. Key advantages of artemisinins over the conventional antimalarials include their rapid and potent action, with good tolerability profiles. Their action also covers transmissible gametocytes, resulting in decreased disease transmission. Up to now there has been no prominent report of drug resistance to this group of compounds. Treatment of malaria in pregnant women requires special attention in light of limited treatment options caused by potential teratogenicity coupled with a paucity of safety data for the mother and fetus. Treatment of other malaria species is less problematic and chloroquine is still the drug of choice, although resistance of P. vivax to chloroquine has been reported. Multiple approaches to the identification of new antimalarial targets and promising antimalarial drugs are being pursued in order to cope with drug resistance.

Pharmacokinetics and pharmacodynamics of intravenous artesunate during severe malaria treatment in Ugandan adults

BACKGROUND

Severe malaria is a medical emergency with high mortality. Prompt achievement of therapeutic concentrations of highly effective anti-malarial drugs reduces the risk of death. The aim of this study was to assess the pharmacokinetics and pharmacodynamics of intravenous artesunate in Ugandan adults with severe malaria.

METHODS

Fourteen adults with severe falciparum malaria requiring parenteral therapy were treated with 2.4 mg/kg intravenous artesunate. Blood samples were collected after the initial dose and plasma concentrations of artesunate and dihydroartemisinin measured by solid-phase extraction and liquid chromatography-tandem mass spectrometry. The study was approved by the Makerere University Faculty of Medicine Research and Ethics Committee (Ref2010-015) and Uganda National Council of Science and Technology (HS605) and registered with ClinicalTrials.gov (NCT01122134).

RESULTS

All study participants achieved prompt resolution of symptoms and complete parasite clearance with median (range) parasite clearance time of 17 (8-24) hours. Median (range) maximal artesunate concentration (Cmax) was 3260 (1020-164000) ng/mL, terminal elimination half-life (T1/2) was 0.25 (0.1-1.8) hours and total artesunate exposure (AUC) was 727 (290-111256) ng·h/mL. Median (range) dihydroartemisinin Cmax was 3140 (1670-9530) ng/mL, with Tmax of 0.14 (0.6 - 6.07) hours and T1/2 of 1.31 (0.8-2.8) hours. Dihydroartemisinin AUC was 3492 (2183-6338) ng·h/mL. None of the participants reported adverse events.

CONCLUSIONS

Plasma concentrations of artesunate and dihydroartemisinin were achieved rapidly with rapid and complete symptom resolution and parasite clearance with no adverse events.

Artesunate: The Best Drug in the Treatment of Severe and Complicated Malaria

This review summarizes progress in treating severe and complicated malaria, which are global problems, claiming at least one million lives annually, and have been accompanied by advances in our understanding of the pathogenesis of severe malaria complications. New drugs such as intravenous artesunate (AS) and intramuscular artemether (AM) are improving outcomes and decreasing malaria deaths. Trials comparing AM to the traditional parenteral drug, quinine, have not demonstrated however convincing evidence of a mortality advantage for AM. The South East Asian Quinine Artesunate Malaria Trials (SEAQUAMAT), a multicenter, randomized, open-label study comparing AS with quinine showed that parenteral AS was shown to be associated with a 35% reduction in the risk of mortality compare to quinine, and is now the recommended treatment by the WHO for severe and complicated malaria in low-transmission areas and in the second and third trimesters of pregnancy, with almost all the benefit reported in those with high parasite counts. Artesunate is a semisynthetic derivative of artemisinin whose water solubility facilitates absorption and provides an advantage over other artemisinins because it can be formulated as oral, rectal, intramuscular, and intravenous preparations. Artesunate is rapidly hydrolyzed to dihydroartemisinin, which is the most active schizonticidal metabolite. Injectable AS results in a more rapid systemic availability of AS compared with intramuscular AM. This pharmacokinetic advantage may provide a clinical advantage in the treatments of severe and complicated malaria.

Effects of concurrent administration of nevirapine on the disposition of quinine in healthy volunteers

Objectives

Nevirapine and quinine are likely to be administered concurrently in the treatment of patients with HIV and malaria. Both drugs are metabolised to a significant extent by cytochrome P450 (CYP)3A4 and nevirapine is also an inducer of this enzyme. This study therefore evaluated the effect of nevirapine on the pharmacokinetics of quinine.

Methods

Quinine (600 mg single dose) was administered either alone or with the 17th dose of nevirapine (200 mg every 12 h for 12 days) to 14 healthy volunteers in a crossover fashion. Blood samples collected at predetermined time intervals were analysed for quinine and its major metabolite, 3-hydroxquinine, using a validated HPLC method.

Key findings

Administration of quinine plus nevirapine resulted in significant decreases (P < 0.01) in the total area under the concentration–time curve (AUCT), maximum plasma concentration (Cmax) and terminal elimination half-life (T1/2β) of quinine compared with values with quinine dosing alone (AUC: 53.29 ± 4.01 vs 35.48 ± 2.01 h mg/l; Cmax: 2.83 ± 0.16 vs 1.81 ± 0.06 mg/l; T1/2β: 11.35 ± 0.72 vs 8.54 ± 0.76 h), while the oral plasma clearance markedly increased (11.32 ± 0.84 vs 16.97 ± 0.98 l/h). In the presence of nevirapine there was a pronounced increase in the ratio of AUC(metabolite)/AUC (unchanged drug) and highly significant increases in Cmax and AUC of the metabolite (P < 0.01).

Conclusions

Nevirapine significantly alters the pharmacokinetics of quinine. An increase in the dose of quinine may be necessary when the drug is co-administered with nevirapine.

In vitro selection of Plasmodium falciparum drug-resistant parasite lines

The in vitro selection of antimicrobial resistance in important pathogens can provide critical information on the genetic basis of drug resistance, and such information can be used to predict, anticipate and even contain the spread of resistance in clinical practice. For instance, the discovery of the role of pfmdr1 in mefloquine resistance in malaria parasites resulted from in vitro studies. However, the in vitro selection of resistance is difficult, challenging and time consuming. In this review, we discuss the key parameters that impact on the efficiency of the in vitro selection of resistance, and propose strategies to improve and streamline this process.

Existing antimalarial agents and malaria-treatment strategies

In the absence of prompt and efficacious treatment, malaria patients may progress within a few hours from having minor symptoms to severe disease and death. These last years have seen the development of several artemisinin-based combinations, new treatments for severe malaria patients, and new strategies such as intermittent preventive treatment or the home-based/near-home management of malaria. The health sector is now confronted with several treatment options and strategies, in contrast with the period when chloroquine monotherapy was the standard treatment. The major challenge remains the large-scale deployment, in the most efficient way, of the tools available today, including artemisinin-based combination treatments, within health systems that remain extremely weak in malaria endemic countries, particularly in sub-Saharan Africa. Health system research, exploring new potential approaches for the large-scale implementation of these interventions, should be promoted in parallel with that on new therapeutic agents to be used in the unlucky event of the emergence and spread of artemisinin resistance. The prospects of substantially decreasing the malaria burden are brighter today than 20 - 30 years ago, but the efforts and resources committed to this purpose should be maintained over a long period.

Effects of concurrent administration of nevirapine on the disposition of quinine in healthy volunteers

OBJECTIVES

Nevirapine and quinine are likely to be administered concurrently in the treatment of patients with HIV and malaria. Both drugs are metabolised to a significant extent by cytochrome P450 (CYP)3A4 and nevirapine is also an inducer of this enzyme. This study therefore evaluated the effect of nevirapine on the pharmacokinetics of quinine.

METHODS

Quinine (600 mg single dose) was administered either alone or with the 17th dose of nevirapine (200 mg every 12 h for 12 days) to 14 healthy volunteers in a crossover fashion. Blood samples collected at predetermined time intervals were analysed for quinine and its major metabolite, 3-hydroxquinine, using a validated HPLC method.

KEY FINDINGS

Administration of quinine plus nevirapine resulted in significant decreases (P < 0.01) in the total area under the concentration-time curve (AUC(T)), maximum plasma concentration (C(max)) and terminal elimination half-life (T((1/2)beta)) of quinine compared with values with quinine dosing alone (AUC: 53.29 +/- 4.01 vs 35.48 +/- 2.01 h mg/l; C(max): 2.83 +/- 0.16 vs 1.81 +/- 0.06 mg/l; T((1/2)beta): 11.35 +/- 0.72 vs 8.54 +/- 0.76 h), while the oral plasma clearance markedly increased (11.32 +/- 0.84 vs 16.97 +/- 0.98 l/h). In the presence of nevirapine there was a pronounced increase in the ratio of AUC(metabolite)/AUC (unchanged drug) and highly significant increases in C(max) and AUC of the metabolite (P < 0.01).

CONCLUSIONS

Nevirapine significantly alters the pharmacokinetics of quinine. An increase in the dose of quinine may be necessary when the drug is co-administered with nevirapine.