Kinetic Driver of Antibacterial Drugs against Plasmodium falciparum and Implications for Clinical Dosing

Abstract

Antibacterial drugs are an important component of malaria therapy. We studied the interactions of clindamycin, tetracycline, chloramphenicol, and ciprofloxacin against Plasmodium falciparum under static and dynamic conditions. In microtiter plate assays (static conditions), and as expected, parasites displayed the delayed death response characteristic for apicoplast-targeting drugs. However, rescue by isopentenyl pyrophosphate was variable, ranging from 2,700-fold for clindamycin to just 1.7-fold for ciprofloxacin, suggesting that ciprofloxacin has targets other than the apicoplast. We also examined the pharmacokinetic-pharmacodynamic relationships of these antibacterials in an in vitro glass hollow-fiber system that exposes parasites to dynamically changing drug concentrations. The same total dose and area under the concentration-time curve (AUC) of the drug was deployed either as a single short-lived high peak (bolus) or as a constant low concentration (infusion). All four antibacterials were unambiguously time-driven against malaria parasites: infusions had twice the efficacy of bolus regimens, for the same AUC. The time-dependent efficacy of ciprofloxacin against malaria is in contrast to its concentration-driven action against bacteria. In silico simulations of clinical dosing regimens and resulting pharmacokinetics revealed that current regimens do not maximize time above the MICs of these drugs. Our findings suggest that simple and rational changes to dosing may improve the efficacy of antibacterials against falciparum malaria.

From Circulation to Cultivation: Plasmodium In Vivo versus In Vitro

“…Gentle shaking of Plasmodium cultures can partially overcome the challenges associated with high hematocrit and parasitemia, while also increasing chances for non-motile merozoites to contact and invade uninfected RBCs. Utilization of non-traditional culture systems that allow for continual flow of RBCs through an in vivo-like environment, such as hollow-fiber capillary bioreactors (HFBRs), further overcomes this problem; HFBRs allow for high parasite replication at physiological hematocrit levels by not only increasing surface area for nutrient exchange but also by allowing continual addition of fresh medium [25][26][27][28][29]. The pumped fluid flow design of HFBRs has specifically facilitated precise in vitro modulation of drug concentrations over time, generating conditions that more closely mimic the pharmacokinetics of in vivo drug treatment [25,26,28].…”

Transmissibility of clinically relevant atovaquone-resistantPlasmodium falciparumby anopheline mosquitoes

“…Asynchronous P. falciparum (0.25% parasitemia, 1.2% hematocrit) in microtiter plates was exposed to serial dilutions of drug (in quadruplicate) for 72h. [ 3 H(G)]-hypoxanthine (16Ci/mmol, 1 mCi/mL NET177001MC, Perkin Elmer) was added for the final 24h, and incorporated radiolabel was evaluated in harvested cells, as described previously (41). EC 50 values were obtained by nonlinear regression analysis (Prism 6; GraphPad).…”

Inhibitory Compounds Targeting Plasmodium falciparum Gyrase B

“…Amongst fluoroquinolones tested, CIP has been reported as having best anti-malaria activity but had off-target (i.e. non-gyrase/Topo IV) toxicity which may have been partially responsible for the killing effect observed (24)(25)(26). In contrast, other reports have shown that fluoroquinolones do not appear to be particularly effective anti-malarial agents against uncomplicated malaria and suggested they should be used together with other standard antimalarials (27,28).…”

“…Indeed, antibacterials have been used against the parasite, including gyrase-targeting ciprofloxacin (CIP), which results in a “delayed death” phenomenon as a result of arresting of growth in the second asexual cycle ( 23 ). Among fluoroquinolones tested, CIP has been reported as having best antimalaria activity but had off-target (i.e., non-gyrase/topoisomerase IV) toxicity, which may have been partially responsible for the killing effect observed ( 24 – 26 ). In contrast, other reports have shown that fluoroquinolones do not appear to be particularly effective antimalarial agents against uncomplicated malaria and suggested they should be used together with other standard antimalarials ( 27 , 28 ).…”

“…For these reasons, we have attempted to discover new molecules that specifically inhibit malarial apicoplast gyrase but not bacterial gyrase. As P. falciparum causes the most severe outcomes among all Plasmodium species ( 24 , 30 ), we chose to work with P. falciparum gyrase ( Pf Gyr) proteins. To test for inhibitors, it is necessary to produce purified Pf Gyr for in vitro experiments.…”