Approaches to reducing subvisible particle counts in lyophilized parenteral formulations

Reduction in subvisible particle counts in parenteral formulations is an important requirement. Despite selection of best container/closure and use of processing conditions where the drug is most soluble and stable, lyophilized formulations often demonstrate problems of subvisible particle counts greater than the permitted compendial limits. We have studied some formulation and processing approaches with different compounds with the intention of developing lyophilized products, which after reconstitution, pass compendial subvisible particle limits for large volume parenterals (LVP). The approaches studied were targeted to reduce "intrinsic" subvisible particle counts and included the addition of a solubilizing agent, pH adjustment, charcoal treatment of the process solution, and use of a filter with finer pore size for filtering the solution prior to lyophilization. Although the relative efficiency of each of these parameters in reducing subvisible particle counts was found to be slightly different for each compound, the inclusion of a solubilizing agent and charcoal treatment of the processing solution were found to have the most pronounced effect. The combination of two or more parameters was often found to be even more effective. It is suggested that these approaches may be useful in developing other lyophilized products that yield low subvisible particle counts on reconstitution.