Effect of polymer excipients on the enzyme activity of lyophilized bilirubin oxidase and beta-galactosidase formulations

The effects of excipients on the protein stability during lyophilization as well as the storage stability of lyophilized bilirubin oxidase (BO) and be ta-galactosidase (GA) formulations were studied using four polymer excipien ts: dextran, polyvinylalcohol (PVA), poly(acrylic acid) (PAA), and alpha be ta-poly(N-hydroxyethyl)-L-aspartamide (PHEA). Denaturation of BO and GA dur ing Lyophilization largely depended on the excipient used. Dextran appeared to cause severe damage to proteins, whereas PHEA protected proteins effect ively from denaturation, Storage stability of BO and GA formulations also d epended on the excipients, such that the formulations containing dextran an d PAA were relatively unstable, Storage stability was improved by absorptio n of a small amount of water for all the formulations studied. Absorption o f a larger amount of water, however, decreased the storage stability of the formulations containing PVA, PAA or PHEA, In contrast, the storage stabili ty of formulations containing dextran did not decrease noticeably with incr easing water. This may be because formulations containing dextran have a hi gher glass transition temperature than formulations containing PVA, PAA or PHEA when a large amount of water is absorbed.