Dehydration kinetics of prostaglandin E1 in a lipid emulsion.

The overall dehydration kinetics of prostaglandin E1 (PGE1) in a lipid emulsion at 35 degrees C were found to fit a model whereby the kapparent measured at each pH is simply the sum of the product of the fraction of the PGE1 at the interface, fi, and the rate constant at the interface, ki, plus the product of the fraction of the PGE1 in the aqueous phase, faq, and the rate constant in the aqueous phase, kaq. The values for fi and faq were reported earlier as a function of pH at 35 degrees C. The kaq and kapparent were experimentally determined as a function of pH at 35 degrees C. The ki was indirectly determined from the stability data in the emulsion. Microscopic rate constants for dehydration of PGE1 in the aqueous phase and interface at 35 degrees C were estimated from the experimental data. Based on the kinetic evaluation performed, it appears that the dehydration kinetics might be manipulated by the addition of charged surface active agents.