Succinate Buffer in Biologics Products: Real-world Formulation Considerations, Processing Risks and Mitigation Strategies

The succinic acid/succinate system has an excellent buffering capacity at acidic pH values (4.5-6.0), promising to be a buffer of choice for biologics having slightly acidic to basic isoelectric points (pI 6 - 9). However, its prevalence in drug products is limited due to the propensity (risk) of its components to crystallize during freezing and the consequent shift in the pH which might affect the product stability. Most of these previous assessments have been performed under operational conditions that do not simulate typical drug product processing conditions. In this work, we have characterized the physicochemical behavior of succinate formulations under representative pharmaceutical conditions. Our results indicate that the pH increases by ∼ 1.2 units in 25 mM and 250 mM succinate buffers at pharmaceutically relevant freezing conditions. X-ray diffractometry studies revealed selective crystallization of monosodium succinate, which is posed as the causative mechanism. This salt crystallization was not observed in the presence of 2% w/v sucrose, suggesting that this pH shift can be mitigated by including sucrose in the formulation. Additionally, three monoclonal antibodies (mAbs) that represent different IgG subtypes and span a range of pIs (5.9 - 8.8) were formulated with succinate and sucrose and subjected to freeze-thaw, frozen storage and lyophilization. No detrimental impact on quality attributes (QA) such as high molecular weight (HMW) species, turbidity, alteration in protein concentration and sub-visible particles, was observed of any of the mAbs tested. Lastly, drug formulations lyophilized in succinate buffer with sucrose demonstrated acceptable QA profiles upon accelerated kinetic storage stability, supporting the use of succinate buffers in mAb drug products.