Solubility Measurements at 296 and 310 K and Physicochemical Characterization of Abiraterone and Abiraterone Acetate

Comparative solubility tests at 296 1 K and 310 +/- 1 K in 11 solvents, PAMPA permeability measurements at 296 +/- 1 K and 310 +/- 1 K in water, FaSSIF-V2 and FeSSIF-V2 media, thermoanalytical investigation, and crystallographic characterization were performed on the active pharmaceutical ingredients abiraterone and abiraterone acetate. Both compounds exhibited < 0.5 g/mL solubility in water. Abiraterone was slightly soluble, while abiraterone acetate was soluble or freely soluble in the organic solvents tested. Both compounds showed increasing solubility in alcohols with longer carbon chain length. Both compounds had the highest solubility in THF, > 10 mg/mL and > 400 mg/mL for abiraterone and abiraterone acetate, respectively, at room temperature. With increasing temperature, the solubility of the compounds only exhibited a marginal increase. Due to their low solubility, abiraterone and its prodrug exhibited very low passive permeability in water and biorelevant media at both 296 +/- 1 K and 310 +/- 1 K. Abiraterone had a melting point of 501 K. For the acetate ester, a 419 K melting point was measured. Neither abiraterone nor the ester showed weight loss up to 473 K by thermogravimetry, indicating no decomposition. The enthalpy of fusion of abiraterone was approximately twice that of abiraterone acetate. Based on the XRD measurements both compounds were crystalline with intensive Bragg peaks.