Mechanisms of adverse effects of drugs
The mechanisms of adverse effects of drugs can be distinguished according to the fact that they are or not linked to their main pharmacological properties.
Undesirable effect directly related to the main pharmacologic effect
The adverse effect appears as an exaggeration of the expected pharmacological effect, because of an overdose or a particular susceptibility of the patient: for example, bleeding under anticoagulant, hypoglycemia after insulin administration.
The unwanted effect is linked to the main mechanism of action of the drug: for example, neuroleptics induce, by their antidopaminergic effect, a rise in prolactin, antineoplastics have many adverse effects because they kill not only the cancerous but also the healthy cells.
Undesirable effect related to a parallel pharmacologic property of the molecule
The majority of the molecules have, in addition to their principal effect, other parallel effects. The tricyclic antidepressants have an anticholinergic effect not necessary for the antidepressant effect, but likely to give adverse effects.
These types of adverse effects linked to the pharmacological properties are generally foreseeable and are known before the introduction of a drug on the market.
Adverse effect unrelated to a known pharmacological property of the drug
It is the case of many adverse effects such as hepatitis, agranulocytosis, occurring with drugs in theory without effect on the liver or the blood cells. The mechanisms of this type of adverse effects are often poorly understood: they are immunologic or toxic (by production of toxic metabolites for example), and occur only in a little number of patients.
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