Radichemical Purity and Stability of Generic Tc-99m DTPA

Objectives Tc-99m diethylene triamine pentaacetic acid (DTPA) is utilized to evaluate Glomerular Filtration Rates (GFR). When using the modified Russell two-point method for GFR studies, the radiochemical purity (RCP) of Tc99m DTPA preparation must be greater than 98%.

Methods Our laboratory evaluated the RCP and stability of low activity (101.3 mCi) and high activity (215.0 mCi) generic Tc-99m DTPA (Anazao Health) preparations at various time intervals ranging from 0.5 to 8.0 hours post formulation, using miniaturized chromatography consisting of Whatman 31ET strips with acetone and Agilant ITLC-SG strips with distilled water. At each specific time interval, three replicate chromatography strips were spotted, developed in the respective solution, cut at the specific cut line, and counted using a NaI(Tl) detector interfaced to a multichannel analyzer. The RCP data was statistically analyzed by calculating the mean and range.

Results The initial radiochemical purity of the low activity Tc-99m DTPA preparation (101.3 mCi) was 99.1% and remained greater than 98.0% up to 8 hours post formulation. For the higher activity Tc-99m DTPA preparation (215.0 mCi), the initial radiochemical purity was 98.6%. The radiochemical purity remained greater than 98.0% for up to 4.5 hours after formulation. At 8 hour post formulation, the radiochemical purity of the high activity preparation was 97.2%, below the recommended purity necessary to perform the modified Russell two-point GFR study.

Conclusions The radiochemical purity and stability of generic Tc-99m DTPA preparations were evaluated to comply to Russell two-point GFR studies. The RCP of Tc-99m DTPA preparations was greater than 98.0% up to 8.0 hours for low activity and up to 4.5 hours post formulation for high activity.