EFFECT OF A CHEMOTHERAPEUTIC DRUG ON THE BIODISTRIBUTION OF TC-99M-DTPA IN BALB C MICE/

The biodistribution of radiotracers used in diagnostic imaging can be grossly and recognizably altered by a wide variety of drugs and other treatment modalities, such as surgery and radiotherapy. Knowledge of s uch altered biodistribution is important both in making diagnostic inf erences from scans and in dosimetric considerations. Vincristine is a drug that has been used as a component of many chemotherapeutic regime ns because of its relative lack of hematologic toxicity. Its mechanism of action is by interfering with microtubule formation. The metabolic fate of vincristine has not been clearly determined and apparently un dergoes in vivo decomposition. We have studied the effect of vincristi ne on the biodistribution of the Tc-99m-DTPA. Vincristine was administ ered by ocular plexus via into female isogenic Balb/c mice. One hour a fter the last dose, Tc-99m-DTPA (7.4 MBq) was injected and after 0.5 h our the animals were rapidly sacrificed. The organs were isolated, the radioactivity uptakes determined in a well counter and the percentage s of radioactivity (% rad) in the organs calculated. The results have shown that the percentage rad has not been significantly altered in pa ncreas, thyroid and brain whilst a significant increased in thymus, ov ary, uterus, spleen, kidney, heart, stomach, lung, liver and bone was reported. The results could be explained by the metabolization and/or therapeutic and immunosupressive action of vincristine.