Methylene blue-enhanced stability of (99mTc)HMPAO and simplified quality control — a comparative investigation

(99mTc)HMPAO is a radiopharmaceutical used for SPECT imaging of regional cerebral perfusion and for labeling cellular blood elements. The addition of methylene blue enhanced the stability of lipophilic (99mTc)HMPAO complex up to 3 h after reconstitution, 86.9±4.2% compared to 49.8±8.9% for the non-stabilised complex and persists over time (86.2±3.5% after 15 min compared to 78.2±4.0% after 3 h). The method widely used for estimation of radiochemical purity is a standard chromatographic procedure which is quite time-consuming taking about 30 min. Comparison of the more rapid and simple solvent extraction method with octanol, which needs only about 10 min to complete, showed a good correlation with the chromatographic method (84.4±4.4% compared to 89.1±4.3%). Using ethyl acetate as solvent instead of octanol gave a slightly higher extraction rate of the lipophilic complex (91.5±5.5% compared to 89.1±4.3%). Further, the ethyl acetate extraction method results in an overestimation, extracting partly secondary complex. It is confirmed, that the stability of the lipophilic (99mTc)HMPAO complex can be increased with methylene blue. The octanol extraction method, using higher extraction volume (up to 3 ml), is recommended as a fast and efficient approach for the quality control in daily clinical routine.