Why are certain drugs (metfomin, birthcontrol, etc.) still biologically active by the time they leave the human body? Shouldn't your kidneys or liver break them down?
When a drug is ingested, it is absorbed into the bloodstream, where it is carried to the body's chemical processing plant, the liver [4]. There, substances are chemically pummeled, twisted, cut apart, stuck together, and transformed by proteins called enzymes [4]. Many of the products of enzymatic breakdown, or metabolites, are less chemically active than the original molecule [4]. Genetic differences can alter how certain enzymes work, also affecting their ability to metabolize drugs [4]. Drugs may be broken down by the body's internal organs, including the kidneys, lungs, GI tract, and liver [1]. Some drugs may remain in the system while the liver and kidneys finish their filtering job [2]. Frequency of use can also affect how quickly a drug is metabolized [3].
When drugs enter the body, the process of elimination begins [1, 5]. In order for drugs to leave the body, most drugs need to be metabolised, which is a chemical process in which the liver transforms the drug into a substance called a metabolite that can be passed out of the body [1, 2]. During this phase, proteins called enzymes break down the drug molecules, which creates metabolites [2]. These metabolites are usually less active chemically than the original drug molecule but may in some cases be equally as powerful or even more so [2]. Metabolism of drugs by the kidney involves two types of reactions: phase I and phase II [6]. The goal of metabolism is to change the active part of medications (also referred to as the functional group), making them more water-soluble and more readily excreted by the kidney [6]. Changing the molecular structure of drugs increases their water solubility and decreases their fat solubility, which speeds up the excretion of the drug in the urine [6]. Drugs can also leave the body in other ways, such as breath and sweat [1].