Dielectric properties of residual water in amorphous lyophilized mixtures of sugar and drug

Dielectric properties of residual water in amorphous lyophilized mixtures of sugar and drug
January 2003
R El Moznine1, G Smith1,3, E Polygalov1, P M Suherman1 and J Broadhead2
1 School of Pharmacy, De Montfort University, Leicester, LE1 9BH, UK
2 AstraZeneca Charnwood R&D, Bakewell Rd, Loughborough, LE11 5RH, UK
3 Author to whom correspondence should be addressed.
Journal of Physics D: Applied Physics
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Abstract
Dielectric relaxation spectroscopy was used to investigate the properties of residual water in lyophilized formulations of a proprietary tri-phosphate drug containing a sugar (trehalose, lactose or sucrose) or dextran. The dielectric properties of each formulation were determined in the frequency range (0.1 Hz?0.1 MHz) and temperature range (30?C?Tg). The temperature dependence of the relaxation times for all samples showed Arrhenuis behaviour, from which the activation energy was derived. Proton hopping through the hydrogen-bonded network (clusters) of water molecules was suggested as the principle mode of charge transport. Significant differences in dielectric relaxation kinetics and activation energy were observed for the different formulations, which were found to correlate with the amount of monophosphate degradation product.