In VivoandIn VitroAntimalarial Properties of Azithromycin-Chloroquine Combinations That Include the Resistance Reversal Agent Amlodipine

Abstract

Evidence of emerging Plasmodium falciparum resistance to artemisinin-based combination therapies, documented in western Cambodia, underscores the continuing need to identify new antimalarial combinations. Given recent reports of the resurgence of chloroquine-sensitive P. falciparum parasites in Malawi, after the enforced and prolonged withdrawal of this drug, and indications of a possible synergistic interaction with the macrolide azithromycin, we sought to further characterize chloroquine-azithromycin combinations for their in vitro and in vivo antimalarial properties. In vitro 96-h susceptibility testing of chloroquine-azithromycin combinations showed mostly additive interactions against freshly cultured P. falciparum field isolates obtained from Mali. Some evidence of synergy, however, was apparent at the fractional 90% inhibitory concentration level. Additional in vitro testing highlighted the resistance reversal properties of amlodipine for both chloroquine and quinine. In vivo experiments, using the Peters 4-day suppressive test in a P. yoelii mouse model, revealed up to 99.9% suppression of parasitemia following treatment with chloroquine-azithromycin plus the R enantiomer of amlodipine. This enantiomer was chosen because it does not manifest the cardiac toxicities observed with the racemic mixture. Pharmacokinetic/pharmacodynamic analyses in this rodent model and subsequent extrapolation to a 65-kg adult led to the estimation that 1.8 g daily of R-amlodipine would be required to achieve similar efficacy in humans, for whom this is likely an unsafe dose. While these data discount amlodipine as an additional partner for chloroquine-based combination therapy, our studies continue to support azithromycin as a safe and effective addition to antimalarial combination therapies.In the last decade, artemisinin-based combination therapies (ACTs) have become widely adopted as first-line treatment in almost all countries where malaria is endemic (90). These drug combinations display excellent clinical efficacy against Plasmodium falciparum infection, yet recent studies from western Cambodia report decreases in parasite clearance rates following artesunate monotherapy or artesunate-mefloquine combination therapy (18,59,60,76,92). The possible emergence of resistance underscores a clear need to find alternative regimens. While several promising agents are in the pipeline, the development of antimalarial drugs that are effective, well tolerated, and safe remains a very challenging task (6,27,77,89). In addition, the new paradigm of antimalarial therapies based on the combination of drugs that have additive or preferably synergistic properties raises the threshold for drug discovery even further.Chloroquine (CQ) was the most important drug for the treatment of malaria for many decades, until widespread resistance led to its replacement, most recently by ACTs (21,93). Recent data from Malawi and Kenya have shown that in those regions, the removal of CQ from local use has led to the resurgence of CQ-sensitive (CQS) strain...

Know your enemy: understanding the role of PfCRT in drug resistance could lead to new antimalarial tactics

“…Alternatively (or in addition), MQ and QN may inhibit PfCRT CQR (e) and/or PfMDR1 (f), and thereby exert part of their antimalarial effect by blocking the physiological functions of these transporters [49,68,75,76,89]. Several resistance-reversers (RR) have been shown to inhibit PfCRT CQR , and the ability to block this form of the protein may underlie the observed increase in the intrinsic antiplasmodial activities of RRs in CQR versus CQS parasites [56,65,69]. Black and green lines indicate transport pathways and red lines denote modes of antimalarial action.…”

Macrolide resistance mechanisms inEnterobacteriaceae: Focus on azithromycin

“…(Allos, 2001;Anonymous, 2013;Crameri & Heininger, 2008;Jimenez et al, 2015;Mitj a et al, 2015;Rolain et al, 2004;Ruiz et al, 2007;Stoner, 2007;Zuckerman, 2004), and have shown activity against some protozoa such as Plasmodium spp. or Toxoplasma gondii (Lee et al, 2011;Pereira et al, 2011). Additionally, despite not showing good activity against nonfermenter Gram-negative microorganisms such as Pseudomonas, macrolides like azithromycin have demonstrated potential to disaggregate biofilms by this micoorganism, and thus, their synergistic effect together with antipseudomonal antibiotics are currently under study to avoid and eradicate Pseudomonas biofilms (Saini et al, 2015).…”

Comparative study of chloroquine and quinine on malaria rodents and their effects on the mouse testis

“…There are some reports on the effects of chloroquine on some species of rodents infected by Plasmodium chabaudi, Plasmodium yoelii and P. berghei [18][19][20] . Since chloroquine and quinine are the most common antimalarial drugs, their therapeutic effects and risk of resistance to drugs were studied.…”