A Study of Microwave Sterilizer for Injection Ampules (No.5): Evaluation of Sterilization Effect on the Head Space of Ampules

Abstract

The heating characteristics, heating parameters, and sterilizing effect of a new type of sterilizer (microwave sterilizer) for the head space of ampules were investigated. A thermographic analysis of the temperature of the head space of the ampules revealed that this system can heat both the solution and the head space to the same level of accuracy, and that the neck of the ampules is a cold spot when they are heated with this device. The two hot-air heaters (X₁ and X₂) were used for heating the head space of the ampules, and the microwave output (X₃) was used for heating the solution within them. Multiple regression analysis was conducted to examine the relationship between the temperature of the cold spot of the head space (Y) and these three parameters (X₁, X₂, and X₃), using ampules containing physiological saline. This analysis yielded the following relationship: Y=0.357X₁-0.023X₂+0.026X₃+4.164 (R=0.998). The following biological indicators were put into the cold spot of the ampule head to evaluate the sterilizing effectiveness of this device: spores of Aspergillus niger (for the low temperature range from 60 to 100°C), spores of Bacillus subtilis (for the medium temperature range from 101 to 120°C), and spores of Bacillus stearothermophilus (for the high temperature range from 121 to 140°C). Challenge tests for these three temperature ranges indicated that this microwave sterilizing system can adequately sterilize the head space of ampules in all temperature ranges.