Development and application of a sterility test for the preparation of technetium-99m radiolabelled red cells using a rapid alternative method

M. Stainmesse1,2, F. Debordeaux1, L. Bordenave3, S. Crauste-Manciet2,4, V. Pottier1 1 Radiopharmacy department – Bordeaux University Hospital – France
2 Pharmaceutical technology department – Bordeaux University Hospital – France
3 Nuclear medicine department – Bordeaux University Hospital – France
4 ARNA ChemBioPharm U1212 INSERM - UMR 5320 CNRS – Bordeaux University – France

Introduction
In nuclear medicine, a patient globular volume is determined through a preparation of autologous red cells pre-treated with stannous pyrophosphate and then radiolabelled with technetium-99m (99mTc-RC).
This preparation is obtained by means of a complex, multi-stage aseptic process, carried out in an open system. This leads to a high-risk level of microbiological contamination.
The objective of this work is to control the absence of microorganism in our preparations thanks to a sterility test, with the aim of validating the red cell radiolabelling process.

Method
A sterility test by rapid alternative method described by the European Pharmacopoeia has therefore been developed. For this, we used the BACT/ALERT® automated system. Due to the limited volume of preparation obtained, paediatric blood culture bottles were chosen.
The sterility testing method was tested with 5 microbiological strains, by performing one growth promotion test on blood culture broth and 3 suitability tests on blood culture broth to which was added 1 mL of our preparation of radiolabelled red blood cells.
The detection limit is being estimated for one strain of bacteria (Staphylococcus epidermidis) using 3 concentrations of bacterial solution on 3 series of 6 blood culture bottles.
Finally, the asepsis of 3 preparations of 99mTc-RC is being tested to validate the preparation process.
A radioactivity decrease was necessary before sending the samples to the bacteriology department. After having inoculated the blood cultures bottles with 1 mL of preparation of 99mTc-RC ± an inoculum, they were stored at room temperature in the nuclear medicine department until the detectable radioactivity was less than 2 times the background noise (approximately 48 h).

Results
The results are in progress for the validation of the sterility test method, the detection limit estimation and the sterility check of the preparation concerning the validation of the radiolabelling process. They are encouraging for the growth promotion test and the suitability tests.

Discussion-conclusion
This sterility test, in addition to an aseptic simulation test, will allow us to validate the asepsis of the 99mTc-RC preparation process. It can also be carried out as part of our operators’ qualification.
Finally, it could be implemented as a routine test to monitor the asepsis of 99mTc-RC preparations. However, this will not be a release control because, due to the radioactive decay, it is accepted by the European Pharmacopoeia that it can be performed after injection to the patient.

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