Physical assessment of the integrity of the overwrapping as a part of the validation of operators for long term microbiological stability of sterile preparations

The aseptic preparation of injectable drugs in controlled areas allows the production of sterile products. When using isolator technology, sterile plastic tubing directly connected through interlocking doors enable to ensure simultaneously the overwrapping of final product and the containment of the sterile content. For long term storage, the question of maintenance of the sterility cannot be entirely answered by sterility testing. As suggested in guidance for industry edited by FDA, physical testing of the integrity of the container and closure system should be as a part of the stability protocol [1] due to the limitations of sterility testing for this purpose. Our objective was to assess the integrity of our overwrapping sealing system. Two physical evaluations were performed on the sealing of the overwrapping:

(i) the measure of tensile strength giving a rupture of the sealing using DY-20B dynamometer (Adamel Lhomargy) with strength cell of 100daN and

(ii) the dye penetration test [2] ASTM F1929-98 (2004) which allows the visual detection of links of the sealing using a mixture of toluidine blue and Triton X 100 surfactant. The physical tests were performed on a 90 µm-thick sterile polyethylene tubing Biosafe® bio 103 (Teleflex medical, Le Faget, France) using a heat seal (S422VM Ora®, Trevoux-France) giving a 2 mm wide seal.

The best sealing condition was fixed using dynamometer measurements for 5 different times of heat sealing from 1 to 3 seconds. Each time of sealing was followed by 3 seconds of contact post heating. The dye penetration test was performed on the best sealing condition fixed with dynamometer, and the variability of the results depending on operators was assessed on 8 operators (6 experienced operators and 2 non-experienced). 5 containers, simulating real overwrapping of end-product, were subjected to 2 heat sealing giving assessment 10 seals per operator. The visual integrity was assessed after 1 month of storage at room temperature. Dynanometric results (daN) for n=3 assays are given in the following table:

The strength of the sealing for the 4.5 s and 5 s is high quality and can be compared to the seal of commercialized bag which was giving 8.3±0.41 daN. With regards to the dye penetration test, a defect was noticed for 11,25 % of the seals (9/80). Reported to the total of sealing performed 4/20 (20%) of the failures were involving not-experimented operators versus only 5/60 (8%) for the experienced operators. Two major defects were identified: the presence of channel within the seal and the lack of seal on the corner. The results pointed out the need for specific education and validation of the operators for sealing procedure to guarantee the integrity of the overwrapping. The dye penetration method could be easily included in the qualification program of operators to guarantee the containment of overwrapping.

In the perspective of extension of storage of aseptic preparations, further investigations are planned in order to validate the packaging stability after thermally conditioning at +4°C and +35°C during 1 month.