Which characteristic differentiates first-generation antipsychotics from second-generation antipsychotics?

First-generation antipsychotics, also known as typical antipsychotics, primarily exert their therapeutic effects by blocking dopamine D2 receptors in the brain. This mechanism is largely responsible for their efficacy in treating positive symptoms of schizophrenia, such as hallucinations and delusions. In contrast, second-generation antipsychotics, or atypical antipsychotics, have a broader mechanism of action; they not only affect dopamine receptors but also impact serotonin receptors, particularly 5-HT2A receptors, which contributes to their effectiveness in treating both positive and negative symptoms of schizophrenia.

Thus, the distinguishing characteristic that sets first-generation antipsychotics apart from second-generation ones is their primary and more selective impact on dopamine pathways without the additional modulation of serotonin pathways that characterize the latter group. This difference in receptor targeting is a critical factor when considering the side effect profiles and therapeutic efficacy of these drug classes.