Bacteriostatic Water reference

Bacteriostatic Water for Injection, USP has no active ingredient or dose of its own: here, "dose" means the volume of diluent added to a given amount of lyophilized peptide, not a fixed number. For example, 2 mL of diluent into a vial with 5 mg of peptide gives a concentration of 2.5 mg/mL; the same vial reconstituted with 1 mL gives 5 mg/mL instead, twice the concentration for the same amount of substance. An error in this calculation shifts not the diluent's properties but the dose of the active substance itself: a larger volume lowers the concentration and requires drawing a larger volume for the same peptide dose, while a smaller volume raises the risk of measurement error when drawing small amounts with a microsyringe. The preservative in the formulation, benzyl alcohol (0.9-1.1%), suppresses bacterial growth across repeated punctures of the stopper: under the USP <797> standard and manufacturer labeling (Pfizer, Hospira), an opened vial is used for no more than 28 days. This is reference information about reconstitution for research protocols, not a medical recommendation and not instructions for self-administration.