A Model of Prefilled Syringes Exposure to Vapor Phase Hydrogen Peroxide (VPHP)

A model was developed that can be used to predict how hydrogen peroxide (H₂O₂) transfers into a liquid drug product that is exposed to vapor phase hydrogen peroxide (VPHP). This model accounts for fluid flow in both the gas and liquid phases as well as the diffusion and convection mechanisms of mass transfer using the first principles of engineering to predict the amount of H₂O₂ that will transfer from the gas to the liquid phase considering a given geometrical system and surrounding conditions. The model was used to investigate how much space is needed in a given container to eliminate convective mass transfer and to create a balance between mass transfer and the air/liquid interface for oxidation-sensitive products in cartridges or vials being filled in an isolator. Experimental results compared well with model predictions. A no-slip boundary condition between the gas and liquid phases was used for the model, which was especially important for the full syringes where convective mass transport predominated. This model may be used to evaluate isolator designs for filling oxidation-sensitive products utilizing the correlation between spiking studies and VPHP uptake to minimize the uptake studies required. It could also be used to inform the design of containers that would minimize the potential for VPHP uptake. For the geometry tested here, it was demonstrated that convection only occurs near the top few millimeters of the container. If the fill level is lower, as it would be for a syringe, the diffusion mechanism of transfer predominates and the rate of transfer of H₂O₂ is much slower. The balance between mass transfer by convection and diffusion should be a consideration in the design of the system to be filled.