Drug metabolism and polypharmacy

As stated by the National Library of Medicine NCBI, a majority of drugs fall under the category of xenobiotics, indicating chemical substances not naturally produced by the body. Xenobiotics undergo diverse physiological processes for detoxification and facilitation their eventual elimination. These processes involve the transformation of drugs into metabolites, collectively referred to as drug metabolism or metabolic biotransformation.
The primary organ responsible for drug excretion is the kidneys; however, lipophilic drugs pose a unique challenge. These substances easily traverse the cell membrane of kidney tubules and may be reabsorbed into the bloodstream. Consequently, lipophilic drugs undergo initial metabolism in the liver before they can be effectively excreted. The metabolism of drugs encompasses various reactions, broadly classified into phase I (modification), phase II (conjugation), and occasionally phase III (further modification and excretion). Drug metabolism is a highly variable process, subject to the influence of multiple factors. A significant disruptor in this process is depot binding. Additionally, enzyme induction plays a role in drug metabolism, where certain drugs induce the production of enzymes, affecting the overall metabolic rate. Furthermore, drugs sharing elements of their metabolic pathways may 'compete' for binding sites on enzymes, leading to a reduction in the efficiency of their metabolism.