Drug-excipient compatibility studies of curcumin and salicylic acid for dermatological formulations

The present study was designed to evaluate the drug-excipient compatibility of curcumin and salicylic acid intended for use in dermatological formulations using Fourier Transform Infrared (FTIR) spectroscopy. Compatibility assessment during the preformulation stage is a critical step in formulation development, as it ensures chemical stability of the active pharmaceutical ingredients, preserves therapeutic efficacy, and minimizes the risk of formulation failure due to undesirable interactions. Curcumin and salicylic acid were subjected to individual characterization and compatibility evaluation in the presence of selected dermatological excipients. Physical mixtures of each drug with individual excipients were prepared in a 1:1 (w/w) ratio and analyzed using FTIR spectroscopy. Spectral scans were recorded over the range of 4000-400 cm⁻¹, and the obtained spectra of the physical mixtures were systematically compared with those of the pure drugs. The analysis focused on identifying any significant changes in characteristic functional group peaks, such as peak shifting, disappearance, or formation of new absorption bands, which could indicate potential chemical interactions. The FTIR spectra of pure curcumin and salicylic acid displayed all characteristic absorption bands corresponding to their respective functional groups, confirming their chemical identity and purity. The FTIR spectra of the drug-excipient physical mixtures demonstrated retention of the major characteristic peaks of both drugs without significant shifts, loss of functional group signals, or emergence of new peaks. Minor variations in peak intensity were attributed to physical mixing rather than chemical interaction. The FTIR compatibility studies confirmed that curcumin and salicylic acid do not undergo chemical interaction with the selected excipients. These findings support the suitability of the excipients for the development of stable, safe, and effective dermatological formulations containing curcumin and salicylic acid.