The effect of the number of withdrawals on the sterility of multidose medication vials.

Policy development with regard to the shelf life of multidose medication vials is difficult because of a lack of sufficient data. The purpose of this study was to evaluate one factor that may play a role in the contamination of multidose vials. We evaluated the effect that the number of withdrawals had on the potential contamination of multidose medication vials. Thirty multidose vials of heparin and 30 multidose vials of lidocaine (lignocaine) were used in the study. Ten vials from each group (heparin and lidocaine) were used as controls and were deliberately contaminated with Staphylococcus aereus at various concentrations (10 colony forming units per millilitre (CFU/ml) to 10(8) CFU/ml). The 20 test vials remaining from each group were then subjected to varying rates of 1-ml fluid withdrawal. Five test vials were sampled every 2 h, five were sampled twice per day, five were sampled once per day, and five were sampled every other day. Each sample was incubated in trypticase soy broth (24 h at 37 degrees C) and Columbia agar with 5% sheep blood (48 h at 37 degrees C). No multidose vials became contaminated regardless of the rate of withdrawals. Some of the deliberately contaminated multidose vials became sterile with time. Lightly contaminated vials (10(1)-10(2) CFU/ml) generally cleared within 10-15 h after initial contamination. The implications of these findings are discussed.