Impact of the freeze-drying on the VHP content in the production of vaccines

Formulation and filling of biological products occur in isolators to avoid contamination and ensure the maximum level of sterility. Isolators are commonly sanitized by vaporized hydrogen peroxide (VHP). Residuals of Hydrogen Peroxide (HP) - in the isolator - may contaminate the solution and trigger instability of the active pharmaceutical ingredients, excipients or entire drug product. The purpose of this work was to investigate the HP consumption during the freeze-drying of a vaccine and establish a thorough understanding of the factors influencing it. The protein formulation and its placebo were spiked with HP and after 2 hours freeze-dried. HP consumption during the lyophilization process was monitored as a function of the time and the freezing temperature. The HP concentration in the spiked formulations during the pre-lyophilization holding period (2 hours) showed a slight decrease. The HP consumption rate, during the freeze-drying, does not depend on its concentration. The presence of the antigen impacts the drying process in terms of HP consumption. Considering a freezing temperature of -55°C, the HP consumption in the protein formulation is higher than in Placebo. 14.6% more of HP is consumed in the protein formulation. This additional HP consumption is most probably due to the oxidation reactions between the HP and the proteins. In case of -45 °C as freezing temperature, the same HP consumption occurred in the protein formulation and in the Placebo. The freeze-drying of the protein formulation removed on average 78.6% of HP with freezing at -45 °C, but only 66% with freezing at -55 °C. During the secondary drying regardless the freezing temperature, the HP concentration decreases with time until it reaches a plateau. The presence of the plateau indicates that the rate-limiting step is the HP diffusion within the sample and not the evaporation from the surface. At a given temperature of secondary drying, the HP content decreases with time and tends to a plateau. Raising the temperature will increase the rate of HP removal until a new rate-limiting plateau is reached.