Optimization of moist heat sterilization.

The use of different combinations of sterilization time and temperature in a pilot scale autoclave, GEV 612 AR-2 (Getinge Ab, Sweden), in optimizing the sterilization process was studied. All three programs used had the same sterilization efficacy (F0 = 15 minutes) but different sterilization temperatures (116, 121, and 126 degrees C) and total process times (98, 57, and 44 minutes). The heat distribution during the sterilization phase was, in all cases, very uniform, the greatest difference being 0.5 degrees C. Also the F0 values differed only by +/- 0.5 minutes from each other. The F0 value increases linearly with all programs until the beginning of the cooling phase. The main effect of different sterilization temperatures on the cumulative F0 curves is an increase in the slope of the curves with increasing sterilization temperature. First order temperature change constants were determined both for the heating phase and the cooling phase. The numeric values of the rate constants for the heating and the cooling phases were 0.20 +/- 0.03 and 0.046 +/- 0.005 min-1, respectively. It is concluded that the pilot autoclave used in this study controls the sterilization process very accurately. The observed variations between F0 values at different positions in the autoclave chamber are acceptable. On the basis of this study an accurately engineered and controlled autoclave is required in process optimization. It also is possible to use higher sterilization temperatures than usually suggested in pharmacopeias and thus to shorten the process time.