Abstract
A high radiochemical purity (RCP) is recommended for radiopharmaceutical compounds used in the clinical practice of nuclear medicine. However, some preparations of 99mTc-sestamibi contain excess impurities (>6%). To understand the origin of these impurities, we investigated the effect of sodium nitrate on the RCP of sestamibi preparations by testing eluates from 3 commercially available 99mTc generators. Methods: The sestamibi kits (Stamicis) were reconstituted with 99mTc eluate from nitrate-containing wet-column (NCWC), nitrate-free wet-column (NFWC), and nitrate-free dry-column (NFDC) generators. Sodium nitrate was 0.05 mg/mL in eluates from the NCWC generators. The RCP was determined using aluminum oxide sheets as the stationary phase and absolute ethanol as the mobile phase. Succimer, tetrofosmin, oxidronate, exametazine, albumin nanocolloid, and soluble albumin were also tested for their RCP values with eluates from the 3 different 99mTc generators. Results: The RCP assessment of 99mTc-sestamibi was performed on 127 Stamicis preparations. Significantly lower RCP values were found for Stamicis kits prepared with the NCWC generator than for Stamicis prepared with the NFWC (P < 0.0001) and NFDC (P < 0.0001) generators. The number of Stamicis preparations with an RCP under 94% was greater with the NCWC generator (32 of 53 kits) than with the NFDC (2 of 51 kits) or NFWC (0 of 23 kits) generator. Furthermore, the addition of a 0.05 mg/mL concentration of nitrate in NFWC generator eluates significantly decreased the RCP of the Stamicis preparation. In the absence of nitrate in 99mTc eluate, no difference was observed between the RCP values of Stamicis kits prepared with the NFWC and NFDC generators. The 99mTc impurities generated by nitrates did not modify the quality of myocardial imaging (normal heart-to-lung ratio, 2.2), probably because these impurities are not in the heart field of view. No other tested 99mTc-radiopharmaceutical interfered with nitrates. Conclusion: We recommend using nitrate-free generator eluates in 99mTc-sestamibi preparations to improve the product quality and prevent unnecessary exposure of the patient to radiation.
Footnotes
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