Effect of pH on Stability of Recombinant Botulinum Serotype A Vaccine in Aqueous Solution and During Storage of Freeze‐Dried Formulations

The purpose of this study was to evaluate the importance of prelyophilization solution pH on the stability of botulinum neurotoxin, serotype A (rBoNTA(Hc)). This understanding is of significant importance for proteins such as rBoNTA(Hc), a potential constituent of a multivalent vaccine product. For multivalent vaccines it may be difficult to identify a liquid formulation satisfying the stability requirements for all constituent protein antigens. Consequently, a lyophilized multivalent vaccine formulation may be a more viable alternative. Therefore evaluating the effect of prelyophilization pH (may be suboptimal) on the stability of antigens such as rBoNTA(Hc) during lyophilization/storage becomes important. We hypothesize that when rBoNTA(Hc) is lyophilized from a suboptimal pH, using the appropriate stabilizers can provide adequate physicochemical stability during lyophilization and long‐term storage. We identified pH 5 and 8 in which the protein was stable and unstable against aggregation. Excipients were identified that could stabilize rBoNTA(Hc) during lyophilization and storage in a stable solution of pH 5. These excipients were 7.5% (w/v) trehalose and 2.5% (w/v) trehalose with 2.5% (w/v) HES, with and without 0.01% (w/v) polysorbate 20. In support of our hypothesis, these excipients were found to provide adequate physicochemical stability to rBoNTA(Hc) during lyophilization/storage, when freeze‐dried from a prelyophilized solution of pH 8. © 2008 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:5132-5146, 2008