Pharmacodynamics and pharmacokinetics.
When we take a tablet, we are usually interested in its immediate effects. The drug is supposed to relieve a headache or reduce symptoms of a cold. At the same time, we may think about the possible side effects it may trigger. The desired and undesired effects that a drug exerts on the body are summarized by the term pharmacodynamics. Conversely, however, the body also exerts effects on the active ingredient. It absorbs it from the intestine, distributes it to the target organs, metabolizes it and finally excretes it again. These processes are called pharmacokinetics and the acronym ADME is used synonymously for them. Pharmacokinetics is concerned with the timing and quantification of these processes. ADME stands for:
- Absorption: absorption into the bloodstream.
- Distribution: distribution in the body
- Metabolism: metabolism to active or inactive compounds.
- Elimination (excretion): excretion, usually via urine or stool.
It is also referred to as LADMET or as ADME-tox. The L stands for liberation, that is, the release of the active ingredient from the dosage form and T/Tox for toxicity.
What happens in the body with active pharmaceutical ingredients?
Release: the first step is to release the active ingredient from the dosage form. Tablets break down into smaller particles and the shell of capsules dissolves. Subsequently, the active ingredients can go into solution and be absorbed into the bloodstream via the cells of the mucosa. Absorption: The passage from the digestive pulp into the bloodstream is called “intestinal absorption”. Various conditions must be met for transport to succeed. It can begin in the stomach, but usually takes place mainly in the small intestine. Distribution: The distribution of the active ingredient throughout the bloodstream, tissues and organs is referred to as distribution. For example, if a bladder infection is treated with antibiotics, the active ingredients must reach the bladder in order to kill the bacteria there. Distribution depends, among other things, on the physicochemical properties of the drug, blood flow to organs, anatomical barriers, and protein binding in the blood. Volume of distribution is used as a measure of distribution. Metabolism: Metabolism, or so-called biotransformation, is a change in the chemical structure of the active ingredient in the body. Very few active ingredients are inert and are excreted unchanged. One goal of metabolism is to facilitate elimination. The aim is to make the exogenous substances more water-soluble so that they can be excreted in the urine. Otherwise, they would remain in the body and possibly cause it harm. Chemical modification also detoxifies foreign substances. Metabolism can already take place in the intestinal cells or subsequently during the first liver passage. In so-called first-pass metabolism, a relevant fraction of the active ingredient may be inactivated, reducing the fraction that finally reaches the target site. Some drugs are inactive in their original form and are only converted into their actual active form by metabolism. These are referred to as prodrugs. Elimination is the irreversible removal of active pharmaceutical ingredients from the body. It consists of excretion and biotransformation. The two major organs for excretion are the kidney and the liver.
