Substance in the organism, whereas bioavailability is a subcategory of the former concept. It is based on the portion of the drug that reaches the final circulatory system. Both of them are highly dependent on the nature of the chemical. Distribution is the process of transferring the drug through the body, and it is influenced by circulation and the target location. Metabolism is biotransformation occurring within the body, which changes and utilizes the chemical, and it is influenced by metabolic pathways. Elimination of the drug can also be considered as excretion of these substances by the bodily systems, and it is determined by its half-life feature and rate of the given process.
These alterations associated with the substance affect a cell’s inner metabolic pathway, which inevitably can lead to side effects and even complications. One of the vital filters of the human body is the liver, which is highly sensitive and vulnerable to drugs with complex stages of its elimination. This means that the main pharmacodynamic concepts include the receptor mechanism, the response curve to the dose, therapeutic index, as well as the development of tolerance, dependence, and the phenomenon of withdrawal. The response to the dosage is a curve of the effective relationship of the medicinal substance on its concentration.
Under the power of the drug is understood the appropriate dose required to achieve a visible effect. Side effects of most drugs are often a direct consequence of their primary pharmacodynamic properties and are better defined by such a concept as unwanted effects. The therapeutic index determines the toxicity or safety of a drug. With a decrease in the sensitivity of a person to the action of a drug prescribed for a long time, there is a development of tolerance. The latter is associated with the appearance of physical dependence, defined as the need to continue taking medicine to avoid the development of withdrawal symptoms. This means that an individual needs to consume the drug to maintain his or her functionality, because, without it, a person loses the optimal level of health and well-being.