Using medium-fill simulation to establish a benchmark microbiological contamination rate for low-risk-level compounding

A benchmark contamination rate for prefilled syringe compounding was determined by using a medium-fill-simulation method. One thousand thirty-five 1-mL tuberculin syringes were aseptically filled with 0.9 mL of sterile soybean-casein digest medium and capped. These syringes were placed into clear nonsterile plastic bags and incubated at 35 degrees C for seven days, then inspected for cloudiness or colony formation indicative of bacterial growth. The operation was performed by two certified pharmacy technicians in an ISO Class 5 vertical-airflow biological safety cabinet in a typical inpatient pharmacy compounding area over two days. The technicians wore protective garments and gloves and followed standard procedures of preparing sterile injections. The adequacy of the methodology was verified by using four syringes that contained deliberately contaminated medium and incubating them along with 15 aseptically prepared syringes at 35 degrees C for seven days. Colony formation in the four syringes containing contaminated medium was directly observed and differentiated from the control syringes, which confirms the validity of the method. No bacterial growth was detected in any of the 1035 medium-filled syringes studied. Therefore, the contamination rate for aseptic compounding operation was less than 0.1%. Medium-fill-simulation testing of 1035 prefilled tuberculin syringes yielded no contamination. A contamination rate of less than 0.1% should be achievable and expected for this type of low-risk pharmacy preparation after pharmacies validate their own compounding operation.