In this work, a systematical compatibility investigation of 6-mercaptopurine and folic acid,
two commonly used medications in the treatment of inflammatory bowel disease, for the needs of a
fixed-dose combination development strategy is shown. Various techniques and approaches, such
as differential scanning calorimetry, isothermal stress testing, attenuated total reflectance–Fouriertransform
infrared spectroscopy, dissolution medium stability and forced degradation studies, were
used to elucidate the possible interactions from different aspects. The results predominantly point
to the absence of physicochemical interactions between the examined substances in a variety of
possible conditions. However, the forced degradation of the blend of substances and excipients in
basic conditions showed a drastic degradation of 6-mercaptopurine, signifying that attention needs
to be directed to the careful selection of the excipients for the formulation. To sum up, our findings
indicate that a fixed-dose combination of 6-mercaptopurine and folic acid could be produced using
one formulation blend, immensely simplifying its manufacture.
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