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.