Impact of Formulation and Suspension Properties on Redispersion of Aluminum-Adjuvanted Vaccines

The adsorption of antigens to the surface of 2 commonly used insoluble adjuvants, aluminum phosphate and aluminum hydroxide, has been well characterized. In spite of the pharmaceutical benefits, alum-based vaccine formulations can present challenges in redispersion of the final product after storage. Inability to resuspend alum-based vaccines during administration results in inadequate dosing, thus rendering the product unusable. Here, the influence of formulation conditions on the resuspendability of aluminum adjuvant-containing vaccines was investigated. Particle size analysis by Micro-Flow Imaging (MFI™), zeta potential measurement, and sedimentation analysis by Turbiscan® were used to characterize suspension properties. Ionic strength, pH, and antigen concentration were found to significantly influence sedimentation behavior, particle size, and redispersion. Increasing ionic strength increased the sedimentation rate of adjuvants favoring resuspendability. The addition of bovine serum albumin to aluminum phosphate reduced resuspendability more significantly than the addition of lysozyme. Decreased resuspendability correlated with an increase in fine-to-large particle ratio and decrease in sedimentation rate. In summary, resuspendability of adjuvant drug product is favored by increased flocculation, decrease in fine-to-large particle ratio, and reduction in surface charge of antigen and adjuvant. A careful balance of these formulation conditions can therefore be an effective means to mitigate challenges of alum adjuvant redispersion.