Pharmaceutical Technology Division Department of Pharmacy University of Helsinki Finland RHEOLOGICAL PROPERTIES OF PHARMACEUTICAL CREAMS CONTAINING SORBITAN FATTY ACID ESTER SURFACTANTS

Korhonen, M., 2003. Rheological properties of pharmaceutical creams containing sorbitan fatty acid ester surfactants. ISBN 952-91-6585-4 (paperback) ISBN 952-10-1476-8 (PDF) The main purpose of the present study was to gain understanding about the rheological (elastic, viscoelastic and viscous) properties of pharmaceutical creams containing sorbitan fatty acid ester surfactants (sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate and sorbitan trioleate). The study investigated the effects of an increase in the hydrocarbon chain length, the double bonded hydrocarbon chains and the concentration of the surfactant on the rheological properties of the sorbitan fatty acid ester surfactant containing creams. In addition, the effects of the volume of inner phase and the short-term storage on the rheological properties of the sorbitan fatty acid ester surfactant containing creams were investigated. The creams studied were either simple, three-component creams, or complex, multi-component creams. The rheological properties were determined with dynamic oscillation stress sweep and oscillation frequency sweep measurements, with static creep recovery measurements and with time-dependent viscosity measurements. An increase in the length of the saturated hydrocarbon chain of the surfactant increased the elastic nature of the creams. A double bond in the hydrocarbon chain of the surfactant decreased, and an increase in the number of double bonded hydrocarbon chains within the surfactant molecule increased the elastic nature of the creams. An increase in the concentration of the surfactant and an increase in the volume of the inner phase increased the elastic nature of the creams. Storage time decreased and storaging the creams at three different conditions levelled off the differences in the elastic properties of the creams. In the three-component cream formulations the rheological properties of the creams were concluded to be mainly due to the interfacial properties of the surfactants. In the multi-component cream formulations the rheological properties of the creams were concluded to be due, in addition to the surfactants used, to the multiphase structures of the creams. Determination of rheological properties, i.e. unrecoverable viscous, partly recoverable viscoelastic and recoverable elastic properties, gave valuable information about the structural and intermolecular properties of the creams. Rheological measurements can be regarded as sensitive tools for detecting structural changes in pharmaceutical creams and should be regarded as an integral part of the quality evaluation of pharmaceutical creams.