Preparation, characterization, intrinsic dissolution studies and microbiological assessment of dapsone tosylate polymorphs

Daniela Flores-Pacheco,Oscar Torres-Ángeles,Blanca E Duque-Montaño,Jorge G Domínguez-Chávez,Jesús Rivera-Islas,Karina Mondragón-Vásquez

doi:10.4314/tjpr.v17i12.1

Abstract

Purpose: To prepare dapsone tosylate salt (TD) and its two polymorphs (TD-I and TD-II), and study their intrinsic dissolution profiles and preliminary anti-mycobacterium activity. Methods: The synthesized product was studied with respect to the effect of solvent selection, reaction temperature and evaporation rate on the solid phase obtained. The polymorphs were characterized using powder x-ray diffraction (PXRD), proton nuclear magnetic resonance ( 1 H-NMR), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV/Vis spectroscopy was employed for quantification of the salt, while Wood apparatus was used for dissolution studies. Microdilution assay, using a 96-well equipment, was employed for the evaluation of anti-mycobacterial activity. Results: On analysis of the solids obtained from synthesis with PXRD, two different patterns were observed. One pattern belonged to TD-I, previously reported, and the other was a new polymorph TD-II. Solvent evaporation was important in the selective preparation of TD-I or TD-II. Analyses with DSC, TGA and 1 H-NMR revealed the absence of solvent in both solids and showed that TD-II was not a solvated salt. Spectral analysis with FT-IR demonstrated structural relationship between TD-I and TD-II. Intrinsic dissolution studies showed that both polymorphs dissolved faster than dapsone (DAP). Conclusion: It is possible to synthesize TD and select the polymorph prepared by means of modulated solvent evaporation rate. The rank order of the intrinsic dissolution rate constants was TD-II > TD-I > DAP. The tosylate salt enhanced inhibitory effect on M. fortuitum, when compared to DAP. Keywords: Dapsone tosylate, Polymorphism, Solid phase characteristics, Intrinsic dissolution, Antimycobacterium activity

Highlights

Dapsone (DAP, 4-((4-aminophenyl) sulfonyl) aniline, Figure 1) is an antimicrobial drug that is usually combined with rifampicin and clofazimine for the treatment Mycobacterium leprae [1]
Cultures of Mycobacterium fortuitum were used on solid TSA agar medium supplemented with 10 % lamb blood and incubated at 37 °C for 48 h
The powder x-ray diffraction (PXRD) pattern of Lot 1 did not fit with TD-I

Summary

INTRODUCTION

Dapsone (DAP, 4-((4-aminophenyl) sulfonyl) aniline, Figure 1) is an antimicrobial drug that is usually combined with rifampicin and clofazimine for the treatment Mycobacterium leprae [1]. From the point of view of the solid drug, DAP has low aqueous solubility (0.85 μg ml-1, Tween 80) [4], crystallizes in spatial group P212121 [5], and there are no reports of polymorphism at room temperature. It undergoes enantiotropic transformation ca 80 °C [6], and some solvates have been reported [7,8,9]. Acedapsone, a commercial derivative of DAP, has five polymorphs [11] In both cases, the selection of the solvent for crystallization is crucial for achieving a single polymorph. The mean value and standard deviation (SD) were obtained from two independent assays performed in duplicate

RESULTS

DISCUSSION

CONCLUSION