Rheological Studies on Different Oily Vehicles for Pharmaceutical Preparations

Aims: The rheological properties of oily vehicles based on patents of non-aqueous vehicles for pharmaceutical suspensions were studied. The effects of different concentrations of suspending agents and different excipients on the flow curves were also investigated. Methods: A Rotovisko viscometer (Haake) fitted with concentric cylinder sensors, NV measuring head± 500 and a temperature controlled water jacket at 37 0C was used. Results: The results showed that Fractionated Coconut Oil (FCO) alone and with 0.7% w/v lecithin exhibited Newtonian behavior. Dispersions of aluminium stearate, hydrogenated castor oil, Cab-o-sil and sucrose in FCO exhibited pseudoplastic behavior. Aluminium stearate 1% w/v and above and the oily vehicle containing aluminium stearate, hydrogenated castor oil, lecithin and sucrose exhibited thixotropic pseudoplastic properties. The omission of lecithin from the later vehicle resulted in a decrease in the apparent viscosity and the loss of thixotropy. Conclusion: The thixotropic pseudoplastic behavior of oily vehicles is a desirable property in liquid pharmaceutical systems that ideally should have a high consistency in the container, yet pour or spread easily after they had been stirred vigorously. Possible reasoning and suggestions were discussed. .