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What is Pharmacokinetics Definition

Pharmacokinetics is the study of the mechanisms and factors influencing entry into the body and efficacy of a drug. The purpose of pharmacokinetics is to choose the route of drug administration (mouth, vein ...).

It allows the adaptation of the dose (dose and frequency of administration) to get better efficiency with minimal adverse effects. Indeed, the low concentrations the drug is ineffective, and high concentrations side effects become too large relative to efficiency.

The body responds positively or negatively towards the molecule which has been administered. It can limit its absorption, inactivate and eliminate it before its metabolism (chemical transformation of the drug by the organs, usually the liver).

How does the drug in the body?
We can schematically distinguish four stages (A, D, M, E) in the pharmacokinetics of a drug:

  • Absorption-resorption (A);
  • Distribution (distribution in the body) (D);
  • Metabolism (chemical transformation) (M);
  • Elimination (excretion) (E).

Absorption is the general circulation from its site of administration (mouth, vein ...). Different dosage forms (formulations) are chosen according to therapeutic goals. For example, a product passes immediately injected into the bloodstream, avoiding the digestive system where it is more or less absorbed.

The digestive absorption depends phenomena of disintegration and dissolution (cachet, capsule ...) that occur in the digestive tract and lead to the release of the active ingredient. When significant diarrhea occurs, for example, the transit time is reduced, the drug is removed before being absorbed, sometimes entirely. Ditto for vomiting: there is no disintegration or passing through the digestive tract, so no effect.

Distribution is the distribution of drug in the body through the bloodstream. The drug is dissolved in the plasma (the liquid part of blood), or it binds to blood proteins that serve as carriers to its pharmacological target.

At the same time it acts on its target, the drug is taken up by organs that transform (or metabolize for professionals).

Metabolism is the phase of the chemical transformations of the active drug. This is mainly metabolized in the liver but also in the lungs, the intestines, or other organs (digestive tract, lungs, kidneys ...) or tissues (skin ...). The liver, because of its vascularity and its richness in enzymes, plays a crucial role. He is the great cleaner or "poor metabolizer" of drugs. This biotransformation residues form called metabolites that can be active, inactive or toxic.

Elimination is the last phase. It corresponds to the excretion of drugs and their metabolites. The main routes of elimination are urinary tract, bile duct (metabolites leave in the stool) and pulmonary (metabolites leave in exhaled air).

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