Development of Tc99m DMSA Complex 2 Quality Control Test

Objectives: ackground Technetium 99m Dimercaptosuccinic acid (Tc99m DMSA) is a diagnostic radiopharmaceutical used for the assessment of renal parenchymal disorders, renal structure, and morphology. Currently no United States drug manufacture is producing the DMSA kit in order to make Tc99m DMSA. Compounding the DMSA kit may be a solution to this shortage. When Technetium99m sodium pertechnetate (Na TcO4-) is added to a DMSA kit, two complexes are formed. Tc99m DMSA Complex 1 is quickly formed and within 10-15 minutes converts to Tc99m DMSA complex¹. Complex 2 is the desired form which localizes in the kidney, whereas complex 1 is readily excreted by the kidneys¹. Oxygen contamination in the kit and an improper ratio of stannous ion (Sn2+) to ligand may favor complex 1 over complex 2 in the chemical reaction². Current radiochemical purity testing does not differentiate between Tc99m DMSA complex 1 and complex 2. The aim of this study was to evaluate the effectiveness of a new radiochemical purity testing method for compounded DMSA which can identify and differentiate Tc99m DMSA complex 1 and complex 2. Materials and Methods A compounded DMSA kit was used with the following formulation: 1.0 mg dimercaptosuccinic acid, 0.42 mg stannous chloride dehydrate, 0.70 mg ascorbic acid, and 50.0 mg inositol dissolved in 2ml of N2 purged 0.9% NaCl. Tc99m DMSA was prepared by adding up to 40mCi of Na TcO4- in 0.1-0.5 ml to the compounded DMSA kit and up to 15 minutes was allowed for the reaction to occur. Three DMSA kits were prepared in this manner and radiochemical purity testing was conducted using ITLC with SA paper (90mm) as a solid phase and methanol for mobile phase¹. Then, an additional ITLC test was performed on each kit to identify Tc99m DMSA complex 2 using 51A paper (90mm x 10mm) as the solid phase and 0.9% NaCl as the mobile phase. The sample origin was placed 15 mm from the bottom of the strip and the strip was developed until solvent front was 85 mm. The developed 51A strip was then scanned using an ITLC scanner. To revert complex 2 back to complex 1 the kits were heated at 100 degrees for 2 hours³. After heating, the Tc99m DMSA solution was filtered through a 0.2 micron filter and passed through a Bio-Gel P-10 column (1cm x 1cm) in order to purify complex 1 from any remaining complex 2². ITLC testing was repeated using the 51A paper and 0.9% NaCl method as described previously on the purified Tc99m DMSA complex 1. Results Radiochemical purity testing for all three kits was ≥ 98% Tc99m DMSA using the SA paper and methanol. The findings of this study are displayed in Table 1. When testing for Tc99m DMSA complex 2 with 51A paper and 0.9% NaCl we found on average that, 87.8% of the radioactive counts were located at the origin and up to 20 mm past origin (15-35 mm from bottom of strip). When testing for Tc99m DMSA complex 1 with 51A paper and 0.9% NaCl we found on average that 80% of the radioactive counts were past 20 mm above the origin (35mm-85mm from the bottom of the strip). Conclusion Using the 51A ITLC paper with 0.9% NaCl is an effective quality control method to identify and differentiate between Tc99m DMSA complex 1 and complex 2. The preferred Tc99m DMSA complex 2 remains mostly at origin with slow migration up the strip, whereas the Tc99m DMSA complex 1 migrates readily up the strip. Performing this quick and simple test on a preparation of Tc99m DMSA can help to ensure the correct complex is present for effective localization and imaging. This test may be more necessary when using compounded formulations of DMSA kits, as opposed to manufactured kits.