Rheological Characterization of Lemon Oil-Loaded Eucerin Cream and Aquaphor Ointment

<b>Background/Objectives</b>: Lemon oil has demonstrated its therapeutic effects in various dermatological diseases, and different dosage forms have been investigated to incorporate lemon oil. Using the existing ointment bases to prepare drug-loaded formulations is a common practice in formulation development. Eucerin and Aquaphor are commonly used ointment bases in pharmacy for compounding preparations to meet patient needs. The maximum drug-loading capacity is an important consideration in order not to compromise desired properties of the ointment bases. The objective of this research was to determine the maximum lemon oil loading capacities by understanding the effects of loading lemon oil into Eucerin and Aquaphor on the rheological properties of the lemon oil-loaded formulations. <b>Methods</b>: Lemon oil was incorporated into Eucerin and Aquaphor at different concentrations. The rheological properties of the formulations were determined in flow and oscillation modes. Creep and recover tests were performed to determine the viscoelastic properties of the formulations. <b>Results</b>: The results showed that addition of lemon oil impacted rheological properties, including viscosity, elastic modulus, viscous modulus, compliance, and strain%, but the overall rheological behaviors remained consistent with the control for both bases. <b>Conclusions</b>: The maximum loading capacity of lemon oil could be determined from rheological testing. The rheological studies provided an important tool to determine the desired formulations for topical applications, without affecting the performance characteristics of the commercial products.