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How can two drugs interact when they use the same liver enzyme?
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Docking of the anticancer drug Gleevec (imatinib) in the abl domain of the bcr-abl tyrosine kinase. Abnormalities in bcr-abl stimulate the continuous proliferation of bone marrow stem cells, causing an increase in myelogenous cells (granulocytes and macrophages) in the body and leading to chronic myelogenous leukemia (CML).
When two drugs compete for the same liver enzyme, they can trigger significant pharmacokinetic interactions that alter how the body processes these substances.12
Because the liver relies on specific enzymes to metabolize drugs, competition for these sites can lead to the following outcomes:
- Inhibition of Metabolism: One drug may act as a competitive inhibitor, binding to the enzyme and preventing the other drug from being processed. When the metabolism of a drug is inhibited, it remains in the body for a longer duration, which can cause its concentration to rise to potentially toxic levels if the drug continues to be administered.342
- Altered Therapeutic Effect: By slowing the breakdown of a drug, the interaction may inadvertently increase its pharmacological effect. Conversely, some drugs can induce the formation of additional enzymes, which accelerates the metabolism of other drugs, thereby decreasing their concentration in the body and reducing their therapeutic effectiveness.2
These interactions highlight the importance of monitoring drug combinations, as they can either lead to unanticipated adverse effects or, in some clinical contexts, be utilized for therapeutic benefit.2