Gravimetric control: accuracy, stability and performances in routine mode

Aim

In-process gravimetric control is our unit choice for the control of cytotoxic preparation. First, the system has been attested and the scale’s stability over time was controlled. Then, we have assessed the performances in routine mode.

Method

We calculated the accuracy (total error in %) with the SFSTP methodology (repeated sampling of sterile water in 1, 3, 5, 10, 30 and 50mL syringes up top 3 days in 4 isolators). Equipment stability has been studied up to 7 days with normalized weights of 2, 20, 200 and 2000g. In the routine mode, samples were non-compliant if the total error was over 5% for volumes > 2mL and 15% for volumes ¡Ü 2mL. Before and after the sample’s correction, the relative error of the theoretical volume (in %) has been calculated.

Outcomes

During the validation, total errors were 3.63%, 2.42%, 4.03%, 5.50%, 1.39% and 1.78% for respective volumes of 1, 3, 5, 10, 30 and 50mL. The scale middle deviations were 1.11%, 0.16%, 0.07% and 0.04% for respective weights of 2, 20, 200 and 2000g. Of 1718 samples (1400 preparations of 28 different drugs), the machine caught 44 samples (2.56%) over the authorized limits (minimal error = 5.08% and maximal error = 55.34%). After correction, the total error for whole samples was, in absolute term, 1.78% ± 1.6%. For the ¡Ü 2mL volume, the total error is 4.19% ± 3.8%.

Conclusion

During activity isolators, the weighting is accurate. The scale’s stability allows a weekly calibration. The total error for the samples is slim, even for smaller volumes (limit reduced at 8% after this study), allowing us to control all our preparations.