Influence of solvents on the crystal habit and properties of rofecoxib and celecoxib: No evidence of polymorphism

Background: In many cases, drugs can exist in more than one crystalline form; the phenomenon is known as "polymorphism." Though the polymorphs are chemically identical, they exhibit different physicochemical properties, viz., melting point, solubility, X-ray diffraction pattern, etc., which further affect the biological properties of drugs. The purpose of this work was to study the effect of solvents on crystallization, solubility and dissolution of rofecoxib and celecoxib. Materials and Methods: The crystals were prepared by using different solvents. The melting point, solubility, dissolution, Fourier-transformed infrared (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) studies were carried out to confirm the polymorphism in drugs. Result: The results indicate that the crystals obtained from different solvents exhibited different physicochemical properties. Though FT-IR and XRD gave an indication of different crystal morphs, DSC proved absence of any polymorphic behavior in the crystals of rofecoxib and celecoxib. Conclusion: Crystals having the desired physicochemical properties may be obtained by selecting solvents of specific polarities.