General Characteristics of the Second Generation
Second-generation drugs differ fundamentally from classical agents in their pharmacological profile. Their main therapeutic feature is that they are effective not only against positive symptoms, but also successfully combat negative symptoms and correct emerging cognitive deficits.
In terms of safety, these agents have a massive advantage: they are much less likely and to a significantly lesser degree to provoke extrapyramidal symptoms, including drug-induced parkinsonism. In addition, they have a milder effect on neuroendocrine regulation, reducing the severity of side effects associated with dopamine receptor antagonism.
Hypotheses of Mechanism of Action
Although the exact detailed mechanism is not yet fully understood, pharmacology highlights several leading theories explaining the properties of atypical antipsychotics:
- Serotonin receptor blockade: key action on the 5-HT2A subtype.
- Reciprocal interaction: a delicate balance between the simultaneous blockade of serotonin (5-HT2A) and dopamine (D2) receptors, ensuring balanced inhibition.
- Binding kinetics: the "fast dissociation" theory, in which a loose and short-lived bond is formed with D2 receptors.
Why Are Extrapyramidal Symptoms Absent?
The absence of severe movement disorders with atypical agents is explained by specific physiology and the localization of processes:
- Receptor ratio: The main factor is the high ratio of 5-HT2A receptor blockade to D2 receptor blockade.
- Reciprocal connections: Inverse relationships exist between the dopaminergic and serotonergic systems.
- Zones of influence: The effect is realized in the nigrostriatal pathway and tuberoinfundibular pathway.
Blocking serotonin 5-HT2A receptors triggers a reciprocal increase in dopamine activity in these areas. This compensatory mechanism completely neutralizes excessive D2 receptor inhibition, protecting the patient from extrapyramidal symptoms and hyperprolactinemia.