Simultaneous determination of amphotericin B, tobramycin and vancomycin in rabbit ocular biofluids and tissues by LC-MS/MS: An antimicrobial therapy for keratitis and its PK-PD application.

A rationale poly-microbial keratitis (PMK) therapy requires quick identification of pathogen (bacteria and fungi) and their efficient treatment. However, majority of healthcare providers are still having trouble finding an effective medicine to treat PMK due to constraints such as antimicrobial resistance, dose and dosing schedule. Thus, a broad spectrum anti-fungal and antibacterial having less resistance in community involving combination therapy such as amphotericin B (AmB), tobramycin (TBR) and vancomycin (VCM) is required. Hence, to characterize the pharmacokinetic (PK) and PK-pharmacodynamic (PD) indices, a rapid and sensitive simultaneous LC-MS/MS bioanalytical method was developed and validated for the quantification of AmB, TBR and VCM in rabbit ocular biofluids and tissues. Chromatographic resolution was achieved on a Zorbax C18 column with a mobile phase composed of acetonitrile and 0.4 % formic acid in deionized water using a gradient mode of elution. The calibration curves showed good linearity over the concentration range of 1.95-500 ng/mL for AmB and TBR, 3.9-800 ng/mL for VCM, respectively. The lower limit of quantification (LLOQ) was found to be 1.95 ng/mL for AmB and TBR, and 4.5 ng/mL for VCM. Analyte extraction was performed by simple protein precipitation method with minimal sample volume of 10 µL. Finally, the developed method was validated for selectivity, linearity (r2 > 0.99), precision, accuracy, matrix effects, and stability. The ocular pharmacokinetic profile of commercial AmB, TBR, and VCM formulations was further assessed using the validated method and the PK-PD indices along with dosing frequency was predicted by PK-PD modelling using Phoenix WinNonlin Software.

Chemical metabolite synthesis and profiling: Mimicking in vivo biotransformation reactions.

Biotransformation was previously viewed as merely the structural characterization of drug metabolites, and it was performed only when drug candidates entered clinical development. The synthesis of drug metabolites is crucial to the drug development process because it generates either pharmacologically active, inactive, or reactive molecules and hence their characterization and comprehensive pharmacological evaluation is necessary. The chemical metabolite synthesis is very challenging due to the complex structures of many drug molecules, presence of multiple stereocenters, poor reaction yields, and the formation of unwanted by-products. Drug metabolites and their chemical synthesis have immense significance in the drug discovery process. The chemical synthesis of metabolites facilitates on- or off-target pharmacological and toxicological evaluations at the easiest. In a broader view metabolite could be a target lead molecule for drug design, toxic reactive metabolites, pharmaceutical standards for bioanalytical methods, etc. Collectively these metabolite information dossiers will aid regulatory agencies such as the EMA and FDA in maintaining strict vigilance over drug manufacturers with regard to the safety of NCE's and their hidden metabolites. Herein, we are presenting a systematic compilation of chemical and biocatalytic strategies reported to date for pharmaceutical drug metabolite synthesis. This review report is very useful for the laboratory synthesis of new drug metabolites, and their preclinical biological evaluation could aid in the detection of early threats (alerts) in drug discovery, eliminate the toxicity profile, explore newer pharmacology, and delivering a promising and safe drug candidate to humankind.

Development and validation of an LC-MS/MS method for the assessment of Isoxazole, a bioactive analogue of curcumin in rat plasma: Application to a pharmacokinetic study.

A novel Isoxazole (ISO) analog of curcumin is synthesized from curcumin and described as having a better pharmacological activity than curcumin, such as anti-cancer, anti-malarial, anti-mycobacterial, and many more. The present research aims to develop a bio-analytical method with a simple, rapid, selective, sensitive, accurate, and precise quantification of ISO by liquid chromatography coupled with tandem mass spectroscopy (LC-MS/MS) in rat plasma matrix. The simple plasma protein precipitation method was used for ISO extraction. The ISO was eluted in isocratic mode on a Water symmetry C18 column (75 × 4.6 mm2, 3.5 µm) at a 600 µL/min flow rate with a 0.1 % formic acid in water and methanol (20:80) as mobile phase. The MS/MS was used as a monitoring tool for the fragmentation of ISO as m/z = 366.1 → 145.1 and m/z = 237.1 → 194.07 for carbamazepine (CBZ; internal standard). The ISO showed good co-relation as (r2 = 0.999) linear and covered a wide range with a lower limit of quantification of 1.0 ng/mL. Finally, the developed method was successfully utilized for oral and intravenous pharmacokinetics of ISO in rats plasma. The absolute bioavailability of ISO was found at about 17.6 % after oral administration.