parameter type tissue distribution PSI-MI Algorithms have been published to predict the value of this parameter but the quality of the prediction is unknown. Accumulation of a drug or chemical substance in various organs (including those not relevant to its pharmacologic or therapeutic action). This distribution depends on the blood flow or perfusion rate of the organ, the ability of the drug to penetrate organ membranes, tissue specificity, protein binding. The distribution is usually expressed as tissue to plasma ratios. MI:2120