Quantitative Tissue Distribution QTD

Distribution studies with radiolabeled test substances in animals are an important part of the drug development process. Routine methods used for these studies are quantitative whole-body autoradiography (QWBA) and alternatively quantitative tissue distribution studies (QTD) with dissection of the animals and measurement of radioactivity in pre-selected organs and tissues using a liquid scintillation counter. 

The results of these studies form the principal basis for the assessment of exposure and the elimination of residues in human organs and tissues, in which direct 

Additionally, before the first study with radiolabeled test substance in man can be started, a risk assessment of a human radiokinetic study is mandatory. The estimation of the radiation exposure in humans given a radiolabeled dose is based on exposure data obtained typically from QTD - or QWBA - studies in animals. 

Blood and plasma samples are taken on Combusto Cones (e.g. PerkinElmer Life Sciences), weighed, dried at room temperature, combusted in a sample Oxidizer (e.g. PerkinElmer Life Sciences, Model Oximate 80/307, Frankfurt am Main, Germany) and the 14 CO2 formed is absorbed with Carbo-Sorb (e.g. PerkinElmer Life Sciences), The subsequent radioactivity measurements are carried out after addition of scintillator to the samples. 

After removal, larger organs and tissues are homogenised with Ultra-Turrax-appliances (e.g. Ika, Staufen, Germany) after addition of deionised water, the amount of which depended on the consistency of 

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