THERMAL INVESTIGATION OF PEG-4000 - OXAZEPAM BINARY-SYSTEM

A thermal study using DSC and Hot Stage Microscopy (HSM) was carried o ut to investigate the interaction in solid state of the binary system PEG 4000 - oxazepam, and to establish their phase diagram. The eutecti c composition, which melting occurs at lower temperature as compared w ith the pure components, has been determined. The results obtained by DSC and HSM have indicated that PEG 4000 - oxazepam mixtures displays no obvious incompatibilities, and that the system shows a typical eute ctic behaviour. However because of the closeness of the melting of PEG 4000 to the eutectic temperature, it was difficult to determine preci sely the eutectic composition and temperature on the basis of DSC meas urements alone. The use of heats of fusion corresponding to physical m ixtures allowed an estimation of the eutectic composition at 6% w/w ox azepam. Additional information of temperature (57.6 degrees C) and com position (5-10% w/w oxazepam) of the eutectic was obtained by HSM usin g the contact method. This low melting temperature in this range of co mpositions offers advantages in terms of drug stability and easy manuf acture.