Effect of refrigeration on bactericidal activity of four preserved multiple-dose injectable drug products

The influence of refrigeration on the bactericidal capability of preservative systems in multiple-dose injectable drug products was studied. Commercially available multiple-dose injectable drug products containing preservatives--atropine/phenol, lidocaine/methylparaben, cyanocobalamin/benzyl alcohol and diphenhydramine/benzethonium chloride--were divided into two groups, one to be maintained under refrigeration (5C) and the other to be maintained at room temperature (25C). In separate tests the multiple-dose vials (MDVs) were individually inoculated with the following organisms: Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Serratia marcescens, and cultured to establish bacterial concentrations at 0, 1, 2, 4, 8 and 24 hours. Bacteria in the preservative systems tested remained viable significantly longer under refrigeration. (Data for diphenhydramine/benzethonium were not obtainable with the methodology used.) It is recommended that sterile medications maintained in preserved MDVs be stored at romm temperature after initial use (i.e., after exposure to possible contamination) unless drug stability considerations dictate otherwise.