Preformulation studies of levonorgestrel: A supplier variation analysis

Levonorgestrel (LNG) is a second-generation synthetic progestogen that has been widely used in oral tablets for emergency contraception, intrauterine devices and transdermal implants. The main objectives of the present work were to evaluate LNG drug substance variability with respect to polymorphism and purity, and to investigate the stability of the compound in the selected organic solvents, pharmaceutical vehicles and biorelevant media. Solid-state analysis of LNG samples from eleven different suppliers were conducted by different analytical techniques, including Fourier transform infrared (FTIR), Raman, solid-state and liquid-state nuclear magnetic resonance (NMR) spectroscopies, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (XRPD), wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). In addition, dynamic vapour sorption (DVS) was performed to investigate the hygroscopicity of LNG. The comprehensive solid-state investigation of LNG from different sources showed only minor variations related to their thermal properties. Overall, all suppliers delivered the same polymorphic form of LNG and the compound displayed high physical stability under elevated temperatures and across relevant organic solvents, suggesting limited risks associated with polymorphic changes during processing. Moreover, the equilibrium solubility was obtained in a wide range of relevant organic solvents, dissolution media and pharmaceutical vehicles, which would support development of new dosage forms containing LNG.