OBJECTIVE: Serotonin (5-HT3) receptor antagonists are promising agents for treatment of neuropathic pain. However, insufficient drug exposure at the central nervous system (CNS) might result in lack of efficacy. The goal of this study was to evaluate the impact of administration of a Pgp inhibitor (tariquidar) on ondansetron exposure in the brain, spinal cord, and cerebrospinal fluid in a wild-type rat model.
METHODS: Ondansetron (10 mg/kg) and tariquidar (7.5 mg/kg) were administered intravenously, plasma and tissue samples were collected and analyzed by HPLC. A mathematical model with brain, spinal cord, cerebrospinal fluid and two systemic disposition compartments was developed to describe the data.
RESULTS: The results demonstrate that tariquidar at 7.5 mg/kg resulted in a complete inhibition of Pgp efflux of ondansetron in the brain and spinal cord. The compartmental model successfully captured pharmacokinetics of ondansetron in wild type and Pgp knockout (KO) animals receiving the drug alone or in wild type animals receiving the ondansetron and tariquidar combination.
CONCLUSIONS: The study provided important quantitative information on enhancement of CNS exposure to ondansetron using co-administration of Pgp Inhibitor in a rat model, which will be further utilized in conducting a clinical study. Tariquidar co-administration resulted in ondansetron CNS exposure comparable to observed in Pgp KO rats. Results also highlighted the effect of tariquidar on plasma disposition of ondansetron, which may not be dependent on Pgp inhibition, and should be evaluated in future studies.

BACKGROUND: The investigation of drug disposition in tissues is critical to improving dosing strategy and maximizing treatment effectiveness, yet developing a multi-tissue bioanalytical method could be challenging due to the differences among various matrices. Herein, we developed an LC-MS/MS method tailored for the quantitation of piperacillin (PIP), cefazolin (CFZ), and cefoxitin (CFX) in rat plasma and 12 tissues, accompanied by validation data for each matrix according to the FDA and EMA guidelines.
RESULTS: The method required only a small sample volume (5 μL plasma or 50-100 μL tissue homogenates) and a relatively simple protocol for simultaneous quantitation of PIP, CFZ, and CFX within different biological matrices. Mobile phase A was composed of 5 mM ammonium formate and 0.1 % formic acid in water, while mobile phase B contained 0.1 % formic acid in acetonitrile. The mobile phase was pumped through a Synergi Fusion-RP column equipped with a guard column with a gradient elution program at a 0.3 mL/min flow rate. The mass spectrometer was operated in positive ionization mode (ESI+) using multiple reaction monitoring.
CONCLUSIONS: The validated method has been successfully applied to quantify PIP, CFZ, and CFX from the plasma and tissue samples collected in a pilot rat study and will further be used in a large pharmacokinetic study. To our knowledge, this is also the first report presenting long-term, freeze-thaw, and autosampler stability data for PIP, CFZ, and CFX in rat plasma and multiple tissues.

Intravenous (IV) iron nanoparticle preparations are widely used to treat iron deficiency. The mechanism of mononuclear phagocyte system-mediated clearance of IV iron nanoparticles is unknown. The early uptake and homeostasis of iron after injection of ferric carboxymaltose (FCM) in mice was studied. An increase in serum iron was observed at 2.5 h followed by a return to baseline by 24 h. An increase in circulating monocytes was observed, particularly Ly6Chi and Ly6Clow. FCM was also associated with a time-dependent decrease in liver Kupffer cells (KCs) and increase in liver monocytes. The increase in liver monocytes suggests an influx of iron-rich blood monocytes, while some KCs underwent apoptosis. Adoptive transfer experiments demonstrated that following liver infiltration, blood monocytes differentiated to KCs. KCs were also critical for IV iron uptake and biodegradation. Indeed, anti-Colony Stimulating Factor 1 Receptor (CSF1R)-mediated depletion of KCs resulted in elevated serum iron levels and impaired iron uptake by the liver. Gene expression profiling indicated that C-C chemokine receptor type 5 (CCR5) might be involved in monocyte recruitment to the liver, confirmed by pharmaceutical inhibition of CCR5. Liver KCs play a pivotal role in the clearance and storage of IV iron and KCs appear to be supported by the expanded blood monocyte population.

Thiazolides are polypharmacology agents with at least three mechanisms of action against a broad spectrum of parasites, bacteria and viruses. In respiratory viruses they inhibit the replication of orthomyxoviridae and paramyxoviridae at a post-translational level. Nitazoxanide 1a, the prototype thiazolide, was originally developed as an antiparasitic agent and later repurposed for the treatment of viral respiratory infections. The second generation thiazolides following nitazoxanide, such as the 5-chloro analogue RM-5038 2a, are also broad-spectrum antiviral agents as we have reported. Both 1a and its effective circulating metabolite, tizoxanide 1b, are 5-nitrothiazole derivatives, while RM-5038 2a and its de-acetyl derivative RM-4848 2b are the corresponding 5-chloro derivatives. Recently 1a has completed phase II-III clinical trials in the United States, Canada, Australia and New Zealand in a total of 2865 adults and adolescents of at least 12 months of age with viral acute respiratory illness. Since its biodisposition is primarily seen in the gastro-intestinal tract, its efficacy in systemic viral diseases requires relatively high oral doses. The chemical synthesis of new derivatives with a better systemic absorption was therefore urgently needed. In order to improve their systemic absorption, new amino-ester prodrug derivatives of 1b and RM4848 2b were prepared and tested for their animal pharmacology, pharmacokinetics and toxicology. RM-5061 8a in rats showed 7-fold higher blood concentration compared to 1a: absolute bioavailability increased from 3 to 20%, with a good safety profile in animal safety pharmacology and toxicology.