Abstract

A quick and reproducible method for radiolabeling of ethionamide, an antitubercular drug, with radioisotope of tecnetium, 99mTc was developed. The radiotracer was evaluated for radiochemical purity, stability, and tissue distribution in normal mice. The 99mTc labeled ethionamide, prepared by using reduced 99mTc demonstrated good labeling efficiency (>85%) and reproducibility. The procedure offers minimum radiation exposure to the radiochemist as handling time is also less. Stannous chloride was used as reducing agent at a concentration of 15 μg/ml at pH 2.0. The radiocomplex was stable till 6 h at 37°. In vitro uptake study of 99mTc labeled ethionamide in Mycobacteria tuberculosis H37RV showed higher uptake in live bacteria. The pharmacokinetic parameters of 99mTc labeled ethionamide, calculated by blood clearance studies in normal New Zealand white rabbits, were found to differ considerably from the native drug. 99mTc labeled ethionamide has low plasma protein binding of approximately 35% and it showed no organ specific accumulation. The radiotracer was f o h d to be a widely and rapidly distributed molecule in the body similar to native drug. Radio labeled ethionamide penetrated all the organs and got cleared off due to short elimination half-life. The scintigraphic studies in infected rabbits confirmed that 99mTc-labeled ethionamide was preferentially taken up by the tubercular lesion.