Demystifying Fogging in Lyophilized Products: Impact of Pharmaceutical Processing

A commonly encountered challenge with freeze-dried drug products is glass vial fogging. Fogging is characterized by a thin layer of product deposited upon the inner surface of the vial above the lyophilized cake. While considered to be a routine cosmetic defect in many instances, fogging around the shoulder and neck of the vial may potentially impact container closure integrity and reject rates during inspection. In this work, the influence of processing conditions i.e. vial pre-treatment, lyophilization cycle modifications and filling conditions on fogging was evaluated. A battery of analytical techniques was employed to investigate factors affecting glass vial fogging. A fogging score was used to quantify its severity in freeze-dried products. Additionally, a dye-based method was used to study solution upcreep (Marangoni flow) following product filling. Our lab-scale results indicate measurable improvement in fogging following the addition of an annealing step in the lyophilization cycle. Pre-freeze isothermal holding of the vials (at 5°C on the lyophilizer shelf) for an extended duration indicated a reduction in fogging whereas an increase in the freezing time exhibited no effect on fogging. Vial pre-treatment conditions were critical determinants of fogging for Type 1 vials whereas they had no impact on fogging in TopLyo® vials. The headspace relative humidity (RH) investigation also indicated sufficient increase in the water vapor pressure inside the vial to be conducive to the formulation of a hydration film - the precursor to Marangoni flow.