Abstract
BACKGROUND: The stability testing of radiopharmaceuticals is a critical aspect of drug development and regulatory approval. The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) provides comprehensive guidelines for stability testing, as outlined in the ICH Harmonised Tripartite Guideline Q1A(R2). In this study, the stability of o-(2-[(18)F]fluoroethyl)-L-tyrosine ([(18)F]FET) and methyl-[(11)C]-L-methionine ([(11)C]MET) was evaluated under GMP conditions to ensure their quality and safety. These radiopharmaceuticals are widely used in brain tumor imaging, yet their stability remains insufficiently studied. Given the short half-life of [(11)C]MET (20 min), rapid preparation and administration are required, whereas the longer half-life of [(18)F]FET (110 min) allows for transportation, making stability considerations crucial due to potential environmental effects on the injection solution. RESULTS: Samples from each batch were tested at different temperatures and pH values across the entire expiration period. The radiochemical purity of [(18)F]FET remained between 98.04 and 100% by TLC, while UPLC values ranged from 95.93 to 99.59%. Differences between these methods stem from their sensitivity and operational principles. While UPLC provides precise separation, it may trap free fluoride, leading to overestimated purity values. In contrast, TLC allows for complete sample evaluation but has lower separation efficiency. Enantiomeric purity assessments confirmed that only the L-form was present, with no detectable D-enantiomer, in the case of [(11)C]MET a maximum of 1.7% D-enantiomer was also detected. Stability remained above the 95% threshold between - 20 and 50 °C, with slight reductions at basic pH values. Even under stressed conditions no decomposition products were detected, and enantiomeric purity exceeded 90%, confirming the robustness of [(18)F]FET and [(11)C]MET stability. CONCLUSION: In this report, the stability of the [(18)F]FET and [(11)C]MET radiopharmaceuticals was studied within the expiration time. [(18)F]FET remained stable until the end of the 12-h expiration time. [(11)C]MET samples stored even under stressed conditions did not decrease under the acceptable limit during the shelf life of the radiopharmaceutical. These findings confirm that both radiopharmaceuticals maintain their stability within the defined shelf life, ensuring their reliability for clinical use. Further studies could explore additional environmental stress factors to enhance stability assessments and optimize storage conditions.