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Nuts and Bolts of Oil and Temperature in Topical Preparations of Salicylic Acid

Abstract Background: Traditional formulations of salicylic acid in ointment bases have disadvantages of being greasy and irritant due to free crystals. Aim: To explore the method for selection of oils and their ratio for topical preparation on the basis of equilibrium solubility study of salicylic acid and to evaluate temperature effect. Materials and methods: Scanning and calibration curve of salicylic acid in methanol were developed. Among available oils, those that had no interference of absorbance of salicylic acid were short-listed for screening purpose. Selections of oils were carried out on the basis of equilibrium solubility study. Compatibility study was made by Fourier Transform Infra-Red spectroscopy analysis. Primitive study of oil mixtures was done. Selections of the ratio of oils were carried out on basis of constrained simplex-centroid design. Results: Salicylic acid had shown linearity in the range of 15-65 μg/mL in methanol at wavelength maximum (300 nm). From the equilibrium solubility study, Parker Neem® Oil (11.81 ± 0.5 mg/g), Isopropyl Myristate (11.29 ± 0.04 mg/g), Mogra Oil (9.62 ± 0.94 mg/g) were selected. The study possessed the same main Fourier transform infra-red peaks of salicylic acid in the salicylic acid-oils physical mixture. 58.64% Parker Neem® oil and 41.36% isopropyl myristate mixture was selected as optimized batch with the desirability of 0.391. Conclusion: The oils mixture could be selected for topical preparation of salicylic acid like paste, cream, ointment etc.