Thermal behavior of naproxen and ketoprofen nonsteroidal anti-inflammatory drugs

Abstract

Nonsteroidal anti-inflammatory drugs naproxen (NAP) ((+)-(S)-2-(6-methoxynaphthalen-2-yl) propionic acid) and ketoprofen (KET) (RS)-(2-(3-benzoylphenyl)-propionic acid) were investigated by thermoanalytical techniques (TG/DTG/DTA, DSC and hot-stage microscopy) and evolved gas analysis (TG-FTIR) for evaluating their thermal behavior. In air, TG curve of NAP presented one mass loss step followed by the burning of carbonaceous material, with final residue of 1.5%, while in nitrogen, a single mass loss step was observed. After melting, if the sample is submitted to an isotherm it evaporates. According to DSC curve, NAP melts at 153.5 °C (∆Hfus = 31.6 kJ mol−1; ∆Sfus = 73.5 J K−1 mol−1) and recrystallizes in the cooling step. These events were confirmed by hot-stage microscopy. TG-FTIR studies revealed that NAP decomposes by releasing 2-methoxynaphthalene and propionic acid. Ketoprofen TG curves in both atmospheres presented a single mass loss. When the sample was kept under isotherm, after melting, it evaporated. From DSC data, the melting at 93.3 °C (∆Hfus=28.4 kJ mol−1, ∆Sfus = 76.9 J K−1 mol−1) was observed, without crystallization or cooling.