Thermodynamic properties and moisture sorption isotherms of two pharmaceutical compounds

Abstract

This investigation examines and compares the water sorption isotherms and the thermodynamic properties of two pharmaceutical preparations (Hypril and Azix) intended to be manufactured with the same process plant and equipment. The moisture equilibrium isotherms were determined at 50, 60 and 70 °C using a gravimetric technique. Five isotherm models were explored for their fitting to the experimental data. Azix showed sigmoid type II isotherms while Hypril showed type III isotherms according to the BET classification. All investigated models fitted well the water sorption isotherms of Hypril. By contrast, only GAB and Adam and Shove equations gave appropriate fit to the experimental data of Azix. For both formulations, the isosteric heat and the differential entropy decreased sharply with the increase of equilibrium moisture content to minimum values and thereafter remain constant. In the case of Azix, the integral enthalpy decreased with equilibrium moisture content while the integral entropy increased until reaching a constant value. Contrariwise, Hypril showed decreasing of the integral enthalpy and entropy with the equilibrium moisture content. Keywords: sorption isotherm, enthalpy, entropy, spreading pressure, pharmaceutical formulations

Experimental Investigation of Moisture Sorption Isotherms for Mefenamic Acid Tablets

“…At constant M, the increase in temperature caused to lower the isotherm curves, for a higher temperature the product had a higher value of relative humidity thereby making it more susceptible to degradation and that agreed with [30]. [33] concluded that For each product, there is an optimum range of water activity values for the best storage conditions.…”