The Presence of Sodium Nitrate in Generator Eluate Decreases the Radiochemical Purity of 99mTc-Sestamibi

Abstract

A high radiochemical purity (RCP) is recommended for radiopharmaceutical compounds used in the clinical practice of nuclear medicine. However, some preparations of 99m Tc-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 99m Tc generators. Methods: The sestamibi kits (Stamicis) were reconstituted with 99m Tc 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 99m Tc generators. Results: The RCP assessment of 99m Tc-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 99m Tc eluate, no difference was observed between the RCP values of Stamicis kits prepared with the NFWC and NFDC generators. The 99m Tc 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 99m Tcradiopharmaceutical interfered with nitrates. Conclusion: We recommend using nitrate-free generator eluates in 99m Tc-sestamibi preparations to improve the product quality and prevent unnecessary exposure of the patient to radiation. Sest amibi labeled with 99m Tc ( 99m Tc-2-methoxyisobutylisonitril, or MIBI) is a lipophilic cationic complex originally developed as a myocardial perfusion imaging agent (1-4) and subsequently used for parathyroid (5) and tumor (6) imaging. Ninety-five percent of intracellular 99m Tc-sestamibi is retained in the mitochondria. Its uptake involves a passive distribution across plasma and mitochondrial membranes, but its retention depends mainly on the large negative transmembrane potential of mitochondria (7). 99m Tc-sestamibi is also a transport substance recognized by the multidrug resistance-related P glycoprotein, and its tumor cell accumulation is enhanced by inhibition of the efflux transport function. This property provided the basis for clinical studies that investigated the role of 99m Tc-sestamibi in predicting the response to chemotherapy in patients with ca...

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An investigation of aspects of radiochemical purity of 99mTc-labelled human serum albumin nanocolloid

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