Evaluation of macro aggregated albumin solution for 99mTc MAA

Objectives Only one commercial kit for the preparation of ^99mTc macro aggregated albumin (MAA) is available in the US. The current method of preparing a particle dependent dosage uses the reconstituted MAA solution to be labeled with ^99mTc. Information on the stability of this solution is lacking. Our objective was to evaluate the stability of MAA solution using radiochemical purity (RCP) and particle size of ^99mTc MAA.

Methods Over 12 months, commercially available MAA reaction vials were reconstituted with normal saline and the solution repackaged into vials containing 500,000 particles per 1 mL in a commercial nuclear pharmacy setting in accordance with USP 797. Vials were stored at 2°C to 8°C for 3 to 14 days before labeling with ^99mTc. Contents were drawn into 3 mL BD syringes and stored at 20°C to 25°C for up to 24 hours. RCP and particle size were evaluated initially and at 24 hours using a method previously described. Correlations between ^99mTc mole fractions and storage times to RCP were calculated.

Results 36 samples were analyzed. Four different lots of MAA were used; n=3, 15, 3, and 12 respectively. The solution was stored for an average of 8 days (SD ± 4 days). The average activity was 34.2 mCi (SD ± 3.8 mCi). The average ^99mTc mole fraction was 0.41 (range 0.17 to 0.59). Storage temperature was 5°C ± 2°C. The mean RCP of the ^99mTc-MAA was 97.7% (range 85.5% to 100%) initially and 96.2% (range 38% to 99.9%) at 24 hours. The size of the particles ranged from 10 to 150 micrometers with 90% being 10 to 50 micrometers. There was a correlation between storage time and RCP (r = -0.25) and ^99mTc mole fraction (r = 0.2).

Conclusions Taking into consideration elution quality and storage conditions, repackaging MAA does not appear to affect the stability of the MAA solution to form stable ^99mTc-MAA. While 34 of our samples met USP RCP parameters of 蠅 90%, two did not. In addition there may be procedures that require higher RCP limits than USP.