The study of the fate of the drug in the body over time is called pharmacokinetics. In contrast to pharmacodynamics, which is the study of the effect of drugs on the body, pharmacokinetics study more readily the body's action on the drug.
The future of medicine is largely dependent on its mode of administration. Basically, there are two basic ways to take medicine: the topical and systemically.
For topical: These ointments, creams, eye drops, ova and vaginal tablets and all medicines to treat diseases without entering the bloodstream. In this case, the future of medicine is simple, since most often it remains on the site of application (skin, eye, etc..) And is eliminated by itself with time or washing.
Systemically: they are all drugs intended to have an effect on the entire body via the bloodstream. In this way, the future of medicine, or rather its active ingredient (the active chemical in it) is commonly divided into four major stages: absorption, distribution in the body, metabolism and the disposal. These steps are not always strictly chronological and can be concurrent.
This step is the passage of the drug in the blood. It is very important because it determines the amount of substance that will penetrate into the body.
It mainly depends on the mode of administration and type of medication. To simplify, there are two major routes of administration: The digestive tract and all the others.
The digestive tract or enteral corresponds to the oral route. When swallowing a tablet, it reaches the stomach and digestion will start: the tablet disintegrates, crumbles and dissolves. Part of the active ingredient may begin to pass through the stomach wall to reach the bloodstream, another continues its path in the intestine before being absorbed to reach the bloodstream. Before the active ingredient does not distribute throughout the body to exert its action, it will pass through the liver and be partially transformed or eliminated: it is the effect of first-pass metabolism.
Parenteral includes all other routes: injection (intravenous, intramuscular or subcutaneous), the transcutaneous route (patches, ointments), of the tongue (granules to melt under the tongue), the rectal (suppositories), etc.. By these means, the active ingredient reaches the bloodstream, is distributed directly into the circulation without undergoing the extensive first pass metabolism. It is said that the active ingredient is more bioavailable than oral: the speed of action or the amount of drug that acts (or both) is more important.
Once past the blood, the drug will be distributed uniformly throughout the body as syrup breaks down in a glass of water. This process is called distribution, drug and affects different parts of the body but not always consistently. The target once achieved, it exerts its action. The target may be a particular type of cell, the focus of infection, etc..
It is step purification of the body that is to say, the phases during which the drug is degraded to be eliminated more easily. Some active ingredients naturally disposal is not the last step.
It occurs mainly in the liver, and occasionally in the kidneys or lungs. The products of these changes are called metabolites and sometimes self-therapeutic activity.
The active and / or its metabolites are excreted through the urinary bladder through (they are found in feces when they are not reabsorbed) or sometimes through the lungs (air expired when the substance 's evaporate easily).