Many drugs pass through the kidneys and come out in the urine unchanged. This is called renal drug clearance . Very few drugs block or slow down the passage of other drugs through the kidneys.
Some drugs pass through the liver and are transformed by chemicals.
This process makes the drugs less toxic and is called metabolism . Many drug interactions have to do with the blockage of or increased rate of metabolism, the blockage of excretion, or a change in absorption. Some drug interactions involve drugs working together or against one another without changing their absorption. These pharmacodynamic interactions can affect how the drug works or its toxicity. Cytochromes are enzymes that work to change the chemical structure of a drug.