| Calculated value | Result | Detailed calculation |
|---|---|---|
| Volume of single cell (B. cereus) | 37.7 μm3 | (max cell radius)2 × π × (max cell length) = 1 μm2 × π × 12 μm |
| Moist mass of single cell | 37.7 pg | Density of bacterial cell = 1 g/mL |
| Total moist mass in contaminated downstream processing sample | 3770 pg/mL | 37.7 pg × 100 cells/mL (= 100 CFU/mL) |
| Total dry mass (B. cereus) | 1131 pg/mL | 30% of 3770 pg/mL |
| Total protein content (B. cereus) | 622.05 pg/mL | Proteins present 55% of total dry mass |
| Fraction of protein exotoxins | 0.311025 pg/mL | Protein exotoxins present 0.05% of total bacterial protein content |
| Number of doses per mL | 0.03 | 22.5 mg/mL drug substance ÷ 750 mg |
| Potential protein exotoxin contamination per dose | 10.3675 pg | 0.311025 pg/mL ÷ 0.03/mL |
| Potential protein exotoxin contamination per kg body weight per day | 0.20735 pg | 10.3675 pg ÷ 50 kg body weight |
| Factor of potential protein exotoxin contamination below TDLo* of Botulinum Toxin Type A | 5.8 | 1.2 pg/kg ÷ 0.20735 pg/kg |
↵* TDLo = Toxic dose low. The lowest dose of a substance which, whatever the dosage form and over an indeterminate time period, causes a documented toxic effect in humans (RTECS Guideline, U.S. Department of Health and Human Services).
Conclusion: A contamination event of a downstream purification pool with 100 CFU/mL of B. cereus resulted in a potential toxin contamination that is below the TDLo of Botulinum Toxin Type A by a factor of 5.8 and therefore does not have an impact on patient safety.