In order to describe the four processes of the pharmacokinetic phase, one is to primarily turn to the definition of the pharmacokinetics. According to Le (2020), pharmacokinetics is essentially the drug’s movement through the body, as well as in and out of it – or, in other words, the body’s processing of the drug. There are four procedures involved in this processing: absorption, distribution, metabolism and excretion, oftentimes abbreviated as ADME.
Absorption refers to the passage of medication molecule from the site of medication administration on to the blood. Factors impacting this process include route of administration – for instance, skin absorption is slow, whereas intravenous one is almost instantaneous – and medication’s ability to dissolve, which largely depends on its form or preparation. Other notable influences are body surface area from which medication is absorbed, blood flow to the site of administration, and lipid solubility of the drug.
Distribution is the following phase, during which medication is allocated within the body to tissues and organs, and, ultimately, to its specific site of action. Factors influencing this step are circulation – that is, various tissues and organs’ vascularity and membrane permeability – the lack of barriers for the drug to pass. Additionally, protein binding – the degree to which medication binds to serum proteins – is something that affects distribution as well.
Metabolism is what the process of the biotransformation of the drug under the influence of enzyme is called. Enzyme detoxifies, degrades and removes biologically active chemicals within the body to make it more hydrophilic, so that the remainders could be excreted. Consequently, the last stage – excretion – is the aforementioned substance removal through the kidneys, bowel, liver, lungs, and exocrine glands. It is worth noting that some drugs may be excreted as metabolites in urine or bile.
Reference
Le, J. (2020). Overview of pharmacokinetics. MSD Manual. Web.