Biodistribution of Technetium- 99m Labeled Diltiazem and Nifedipine in Normal Mice

Diltiazem and nifedipine were labeled with 99mTc by Sn++ reduction method with an efficiency of greater than 99% as determined by ITLC. The biodistribution of both agents were studied in normal mice at various intervals. Scintigrams were also obtained at 1 hour post-injection of mice and at 30 min intervals up to 3 hours in rabbits. Our results indicated a very high accumulation in liver (max. 61.4±10.0 %/g for 99mTc-diltiazem and 36.1±0.6 %/g for 99mTc-nifedipine) with negligible uptake by other organs in mice. Chromatographic analyses of urine samples indicated excretion of a soluble metabolite of 99mTc-diltiazem in high quantity (89.6±3.6 % of the total radioactivity in the urine). Because of high liver accumulation and no selective uptake in myocardium (max. 0.72±0.01 %/g for 99mTc-diltiazem and 0.312±0.224 %/g for 99mTc-nifedipine) the labeled compounds cannot be used for the scintigraphic visualization of myocardium.