The effect of surfactant on drug-plastic sorption phenomenon in solution

The sorption of calcitriol into PVC from an injectable formulation containing Tween 20, a nonionic surfactant, was studied. The amount of drug sorbed by the plastic decreased as the concentration of the surfactant increased. The apparent partition parameter of the drug between PVC strips and the solution was experimentally determined at three different concentrations of the surfactant. A physical model was developed to describe mathematically the partition equilibrium of the drug between the plastic solid phase, the micellar phase of the surfactant, and the aqueous phase of the solution. This model also allowed the calculation of the drug/plastic and drug/micelle partition parameters using the experimentally determined apparent partition parameters.