# Full green assay of parenteral dosage forms of polymyxins utilizing xanthene dye: application to content uniformity testing

## TL;DR

A new green method using a xanthene dye is developed to measure polymyxin antibiotics in parenteral dosage forms without organic solvents.

## Contribution

The first green, solvent-free spectrophotometric method for quantifying colistin and polymyxin B in parenteral formulations.

## Key findings

- Ion-pair complexes with Erythrosine B enabled detection at 558 nm without organic solvents.
- The method followed Beer-Lambert’s law for colistin (1–6 µg/mL) and polymyxin B (1–9 µg/mL).
- The technique was validated and successfully applied to parenteral dosage forms with high recoveries.

## Abstract

Due to the lack of other treatment options, a rebirth of polymyxins is urgently required. Colistin (also called polymyxin E) and polymyxin B are the only two examples of this antibiotic class that were effectively employed in such critical situations. In the present work, both of the two studied medications were quantified via a simple, green, and non-extracting spectrophotometric approach based on the formation of ion-pair complexes with Erythrosine B. Without using any organic solvents, the pink color of the created complexes was detected at wavelength = 558 nm. To achieve the highest intensity of absorbance, optimum conditions were established by the screening of many experimental factors such as pH, buffer volume, the volume of Erythrosine B, and the time consumed to undergo the reaction. For Colistin and Polymyxin B respectively, Beer-Lambert’s law was observed at the concentration ranges of 1–6, 1–9 µg mL− 1. The technique was approved and validated following ICH recommendations. Lastly, the suggested approach has been successfully implemented to quantify the cited medications colorimetrically, for the first time, in their parenteral dosage forms with excellent recoveries. Also, Content uniformity testing was implemented.