Determination and prediction of solubilities of active pharmaceutical ingredients in selected organic solvents

The aim of this work was to measure the solubilities of active pharmaceutical ingredients (APIs) in various organic solvents using the synthetic-visual method. Two non-steroidal anti-inflammatory drugs, i.e., acetylsalicylic acid and acetaminophen, and two histamine H2 receptor antagonists, i.e., cimetidine and famotidine, were selected as the APIs. The solubilities of these APIs in different organic solvents, namely methanol, ethanol, 2-propanol, 1-octanol, and poly(ethylene glycol) 400, were determined in the temperature range of 260-360 K. Cimetidine and famotidine, which have several polymorphs, were characterized using powder X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry before the solubility measurements. The experimental results for the APIs except famotidine show that the solubilities at a given temperature decreased with increasing carbon number of the alcohol. The solubility data were represented by two activity coefficient models: NRTL and UNIQUAC. In addition, predictions of the solubilities using the group contribution models Pharma Modified UNIFAC and modified UNIFAC (Dortmund) were also performed. The predictions obtained using Pharma Modified UNIFAC were better than those obtained using modified UNIFAC (Dortmund).