THE EFFECT OF SURFACTANT ON DRUG-PLASTIC SORPTION PHENOMENON IN SOLUTION

The sorption of calcitriol into PVC from an injectable formulation con taining Tween 20, a nonionic surfactant, was studied. The amount of dr ug sorbed by the plastic decreased as the concentration of the surfact ant increased. The apparent partition parameter of the drug between PV C strips and the solution was experimentally determined at three diffe rent concentrations of the surfactant. A physical model was developed to describe mathematically the partition equilibrium of the drug betwe en the plastic solid phase, the micellar phase of the surfactant, and the aqueous phase of the solution. This model also allowed the calcula tion of the drug/plastic and drug/micelle partition parameters using t he experimentally determined apparent partition parameters.