Ever wonder what happens when medications enter into the body? This lesson will discuss the basics of pharmacokinetics from the time the medication enters the body until the point of excretion.
Definition of Pharmacokinetics
Pharmacokinetics refers to what happens to a medication from entrance into the body until the exit of all traces. Four processes encompass the pharmacokinetics of a medication. They are absorption, distribution, metabolism, and excretion. Each of these processes is influenced by the route of administration and the functioning of body organs.
Let’s look at these processes in further detail.
Absorption and Distribution
Absorption refers to the movement of a medication from where it entered the body to the bloodstream. Enteral medications are typically absorbed through the stomach or intestinal mucosa. These include any medication that is taken by mouth.
Factors that can influence absorption of enteral medications are food in the stomach, drug solubility, and blood flow.Another route of absorption is the parenteral route, which typically refers to medications that are injected. The rate of absorption will vary depending on the type of injection.
Intravenous medications are associated with this category. They are injected directly into the bloodstream, and therefore are absorbed the fastest. Additionally, intramuscular medications, or those where medication is injected deep into the muscles, are absorbed more rapidly than subcutaneous injections, where medication is injected into the tissue between the skin and muscle, due to the increased blood supply provided to the muscles.After absorption comes distribution, or transport of the medication via the bloodstream to the intended action site. The blood supply to the area will determine the rate of distribution. For example, areas such as the heart and brain have an increased blood supply, so medication will act more rapidly in these areas.Medication is also distributed to areas of metabolism and excretion since once a medication enters the bloodstream it’s distributed throughout the body.
Factors that influence distribution include, but are not limited to, the chemical consistency of the medication, the amount of medication, potential drug-drug interactions, local blood flow, and membrane permeability.
Metabolism and Excretion
Metabolism refers to the breakdown of medication into an inactive form. Metabolism is also referred to as biotransformation because of the effect on the chemical consistency of medication. The primary organ of medication metabolism is the liver, although some medications are metabolized in the kidneys, lungs, and intestinal tract, to name a few. Factors that influence the metabolism of a medication are the functioning capacity of the metabolizing organ and an individual’s overall health status.Excretion refers to the elimination of medication from the body.
The primary organ of excretion is the kidneys. Other organs that play a role in excretion are the bowels and the liver. Once medications are metabolized by the liver, they tend to become more water-soluble. This increased solubility increases the absorption of the metabolites by the kidneys through filtration. Factors that increase excretion include the functioning of the excretion organs.
Other Concepts of Pharmacokinetics
There are also time frames associated with the metabolism of medication. One of these is half-life, which is the amount of time it takes for half of the medication dose to be eliminated from the body. Another concept, onset, refers to the amount of time needed for the medication to reach a therapeutic effect. Peak is when the medication reaches the maximum therapeutic response, and duration of action refers to the amount of time the medication maintains a therapeutic response within the body.
The trough is when the medication is at its lowest concentration within the circulatory system.These concepts are very important, especially considering that alterations in organ function have a direct effect on these time intervals. The dosing of some medications depends on these concepts of pharmacokinetics.
Pharmacokinetics refers to what happens to a medication from entrance into the body until the exit of all traces.
Beginning with absorption into the bloodstream, the process proceeds to distribution via the circulatory system, metabolism – when the medication is broken down, and excretion – when the medication is eliminated.This process is always the same, but its length can vary due to factors such as the way the medication was administered, the chemical consistency and amount of the medication, and the functioning capacity of organs involved in metabolism and excretion.