Compatibility study between antiparkinsonian drug Levodopa and excipients by FTIR spectroscopy, X-ray diffraction and thermal analysis

Levodopa (L-Dopa or LD) is nowadays considered one of the essential medicines in the World Health Organization list, being a main treatment component for Parkinson's disease. This paper deals with the investigation of solid-state stability and compatibility of binary mixtures of Levodopa with various pharmaceutical excipients, by employment of several instrumental techniques, such as attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, powder X-ray diffraction (PXRD) data and thermal analysis (TG/DTG/HF). Along L-Dopa, eleven pharmaceutical excipients were investigated, namely calcium lactate (CaL), mannitol (Man), magnesium stearate (MgSt), anhydrous lactose (LAnh), talc (T), magnesium citrate (MgC), sorbitol (Sb), silica (SiO2), polyvinylpyrrolidone K30 (PVP), sodium carboxymethylcellulose (NaCMC) and starch (St). FTIR analysis suggested possible interactions with calcium lactate, mannitol, magnesium stearate, anhydrous lactose, talc and SiO2, which were confirmed by PXRD patterns, except for talc. When the samples were subjected to thermal stress, solely magnesium citrate did not present interactions in binary mixture, while all other excipients were incompatible with L-Dopa.