Antipsychotic Medications

Learning Objective Two: Antipsychotic Medications

Overview of Antipsychotic Medications

Antipsychotic medications are divided into two primary categories: first-generation antipsychotics (FGAs), known as typical antipsychotics, and second-generation antipsychotics (SGAs), known as atypical antipsychotics. The FGAs were the first antipsychotic drugs developed and approved for use, while SGAs are more recent innovations intended to improve upon the limitations of FGAs.

Mechanism of Action

First-Generation Antipsychotics (FGAs)

  • The exact mechanism of action of antipsychotics is not entirely understood, though the primary action of FGAs is the antagonism of dopamine receptors, particularly the D2 receptor subtype.

  • In conditions like schizophrenia, where there is an excess of dopamine activity, FGAs function to reduce this activity to normalize the level of dopamine in the central nervous system (CNS).

  • In addition to dopamine receptors, FGAs also have antagonistic effects on:

    • Muscarinic receptors (anticholinergic action)

    • Histamine receptors (antihistaminergic action)

    • Serotonin receptors (anti-serotonergic action)

    • Alpha-1 adrenergic receptors (may cause low blood pressure or hypotension)

Second-Generation Antipsychotics (SGAs)

  • SGAs, while also antagonizing dopamine receptors, have a broader action on various other neurotransmitter systems, which include serotonin and histamine receptors.

  • SGAs are designed to avoid some of the extrapyramidal symptoms (EPS) seen with FGAs by having a lower affinity for D2 receptors.

Common Adverse Effects of Antipsychotics

First-Generation Antipsychotics (FGAs)

  • FGAs carry a significant risk of extrapyramidal side effects (EPS), which can manifest as muscle movements that are abnormal and involuntary. Specific adverse effects include:

    • Dystonic Reactions: Muscle contractions and abnormal posture.

    • Akathisia: A feeling of inner restlessness and an uncontrollable urge to be in constant motion.

    • Tardive Dyskinesia: Characterized by repetitive, involuntary movements, such as lip smacking, eye twitching, and jerking of limbs.

  • Other adverse effects include:

    • Endocrine disturbances leading to hormonal imbalances (e.g., lactation in non-pregnant women, gynecomastia in men).

    • Sedation, which may be desirable in some cases but can lead to daytime drowsiness.

    • Blurred vision and constipation as common side effects.

    • Neuroleptic Malignant Syndrome (NMS): Life-threatening condition characterized by severe muscle rigidity, fever, and autonomic instability, resulting from prolonged antipsychotic use.

Second-Generation Antipsychotics (SGAs)

  • Though they have a lower risk of EPS, SGAs are associated with a different profile of side effects, which can include:

    • Increased risk of developing Type 2 Diabetes and significant weight gain due to increased appetite.

    • Blood Dyscrasias: Changes to blood cell production in the bone marrow, leading to various hematological issues.

    • Cardiac effects, such as Cardiac Dysrhythmias, which can prolong the QT interval during the repolarization phase of the cardiac cycle, leading to potential arrhythmias.

    • Sedation effects, which can be beneficial at times, but also lead to excessive drowsiness.

    • Lowering of the seizure threshold, potentially increasing the likelihood of seizures in susceptible individuals.

    • Galactorrhea: The abnormal discharge of milk-like substance from the breasts due to hormonal imbalances.

Clinical Considerations

First-Generation Antipsychotics

  • FGAs are used for both acute and chronic psychotic conditions, including schizophrenia and acute behavioral disturbances.

  • These medications can be used in specific scenarios, such as providing behavioral control in psychiatric emergencies or as an off-label antiemetic for severe hyperemesis in pregnancy when other medications have failed.

  • Healthcare providers must carefully manage the potential adverse effects and monitor for signs of EPS or NMS.

Second-Generation Antipsychotics

  • SGAs may take longer to show effectiveness, typically around two weeks to see initial responses, and full therapeutic effects may not be observed for up to three months.

  • Clozapine, a notable second-generation antipsychotic, is used under strict conditions due to its severe adverse effects, but it has demonstrated effectiveness in managing treatment-resistant schizophrenia.

  • Continued monitoring is essential given the potential for metabolic syndrome and other cardiometabolic risks associated with these medications.

Summary of Adverse Effects by Antipsychotic Category

  • A comparative overview indicates that older Phenothiazines (FGAs) are associated with significant EPS, while newer SGAs, such as Clozapine, Quetiapine, and Olanzapine, exhibit lower rates of EPS but higher risks of metabolic side effects, sedation, and other pharmacological complexities.

Conclusion

  • The choice of antipsychotic medication is influenced by multiple factors, including patient demographics (e.g., age, gender), symptom severity, and previous medical history. Determining the most appropriate antipsychotic requires a tailored approach, balancing the therapeutic benefits against the risk of potentially debilitating side effects. Regular monitoring for effectiveness and adverse effects is crucial in optimizing patient outcomes, especially with the diverse profiles of antipsychotics used in clinical practice.