In Vitro Activities of Primaquine-Schizonticide Combinations on Asexual Blood Stages and Gametocytes of Plasmodium falciparum

Abstract

Currently, the World Health Organization recommends addition of a 0.25-mg base/kg single dose of primaquine (PQ) to artemisinin combination therapies (ACTs) for Plasmodium falciparum malaria as a gametocytocidal agent for reducing transmission. Here, we investigated the potential interactions of PQ with the long-lasting components of the ACT drugs for eliminating the asexual blood stages and gametocytes of in vitro-cultured P. falciparum strains. Using the SYBR green I assay for asexual parasites and a flow cytometry-based assay for gametocytes, we determined the interactions of PQ with the schizonticides chloroquine, mefloquine, piperaquine, lumefantrine, and naphthoquine. With the sums of fractional inhibitory concentrations and isobolograms, we were able to determine mostly synergistic interactions for the various PQ and schizonticide combinations on the blood stages of P. falciparum laboratory strains. The synergism in inhibiting asexual stages and gametocytes was highly evident with PQ-naphthoquine, whereas synergism was moderate for the PQ-piperaquine, PQ-chloroquine, and PQ-mefloquine combinations. We have detected potentially antagonistic interactions between PQ and lumefantrine under certain drug combination ratios, suggesting that precautions might be needed when PQ is added as the gametocytocide to the artemether-lumefantrine ACT (Coartem).A sexual multiplication of the malaria parasites in human blood is associated with the morbidity and mortality due to the disease. The gametocyte, the sexual stage of the parasites, is the obligatory link perpetuating the parasite's life cycle into the Anopheles vectors. While most antimalarial drugs target the asexual intraerythrocytic stages of the malaria parasites, it has been increasingly recognized that drugs with actions on the gametocyte stages are critical for severing this transmission link (1, 2). In particular, interruption of malaria transmission is a major challenge for malaria elimination (3). Among the currently used antimalarial drugs, primaquine (PQ) is the only one with gametocytocidal activity on late-stage gametocytes (4). This drug has been used since the 1950s primarily in combination with chloroquine (CQ) as a radical cure for preventing relapses due to Plasmodium vivax. Presently, it is used in combination with CQ or artemisinin combination therapies (ACTs) for radical cure of relapsing malaria parasites due to P. vivax and Plasmodium ovale. In 2012, the World Health Organization (WHO) recommended the addition of a single dose of 0.74 mg/kg PQ as a gametocytocidal agent to reduce P. falciparum transmission in low-transmission settings, particularly in areas under the threat of artemisinin resistance (5). Later in the same year, the WHO Malaria Advisory Committee modified their recommendation to a single 0.25-mg/kg PQ dose to alleviate concerns of serious toxicity in patients with glucose-6-phosphate dehydrogenase deficiency and in consideration of the benefits of disseminating PQ as a transmission blocking drug to a high proportion of patien...

A humanized mouse model for sequestration of Plasmodium falciparum sexual stages and in vivo evaluation of gametocytidal drugs

“…In contrast, in 10 untreated mice from 3 independent infection experiments, the average gametocytemia increased from 0.045% to 0.325% during the 9 days following appearance of gametocytes in peripheral blood. As expected, asexual stages were also eliminated from peripheral blood after 3 to 6 days, since primaquine treatment at 2 mg/kg represents a dose 1000-fold upper the IC50 of primaquine on asexual stages 25 26 ( Supplemental Figure S1 ). In addition, the efficacy of primaquine to eliminate gametocytes from sequestration sites was evaluated in Giemsa-stained smears of bone marrow aspirates and spleen extracts and compared to the average of gametocytemia in 10 untreated mice ( Fig.…”

Efficacy and Safety of Pyronaridine-Artesunate plus Single-Dose Primaquine for Treatment of Uncomplicated Plasmodium falciparum Malaria in Eastern Cambodia

“…However, the single-dose 15-mg primaquine regimen has been extensively reviewed and is considered safe in G6PDdeficient individuals, with no requirement for prior G6PD testing (30). Since primaquine has no activity against falciparum asexual stages (31), its use in this protocol would not have affected the efficacy results obtained for pyronaridine-artesunate. The impact of primaquine on gametocyte carriage was not evaluated in this study.…”

Interactions between tafenoquine and artemisinin-combination therapy partner drug in asexual and sexual stage Plasmodium falciparum

“…In Leishmania and Trypanosoma , TFQ has been reported to interfere with mitochondrial function leading to apoptosis (Carvalho et al., 2010, Carvalho et al., 2015), an activity reminiscent of that of PMQ on Plasmodium erythrocytic stages (Beaudoin and Aikawa, 1968) and gametocytes (Lanners, 1991). However, in accordance with other findings, TFQ by itself was ineffective in inhibiting asexual-stage parasites as compared to the ACT-partner drugs, suggesting that its effects relating to hemoglobin digestion may be insignificant (Bray et al., 2005, Gorka et al., 2013, Cabrera and Cui, 2015). …”