Antipsychotics

Antipsychotics are a heterogeneous group of substances used primarily to treat schizophrenia, psychosis, mania, delusions, and states of agitation. The term neuroleptics was formerly used interchangeably with antipsychotics because early antipsychotic drugs induced apathy, quiescence, and reduced psychomotor activity, but newer antipsychotic drugs no longer have these effects. The antipsychotic effect of first-generation (typical) antipsychotics (e.g., haloperidol) is based on D₂ antagonism, while second-generation (atypical) antipsychotics interact with several receptors (e.g., D₂, D₃, D₄, 5-HT). Extrapyramidal symptoms, which include acute dystonia, akathisia, and tardive dyskinesia, are the most common side effects of first-generation antipsychotics. Metabolic side effects (e.g., weight gain, insulin resistance), on the other hand, are more typical of second-generation antipsychotics. A potentially life-threatening side effect of both first-generation and second-generation antipsychotics is neuroleptic malignant syndrome, which manifests with fever, muscle rigidity, autonomic instability, and mental status changes.

References:^[1][2]

Extrapyramidal symptoms (EPS)

• Definition: : a collection of movement disorders that are typically due to disruption of dopaminergic pathways in the basal ganglia, resulting in bradykinesia, rigidity, dystonia, athetosis, chorea, ballismus, akathisia, tics, and tremors
• Etiology: All antipsychotics that interact with the D₂ receptor may cause EPS, but the probability of this side effect is significantly higher with high-potency antipsychotics.
  • Metoclopramide, although not an antipsychotic, may also cause extrapyramidal symptoms.
• Pathophysiology: Inhibition of the nigrostriatal dopaminergic pathways results in EPS.
  • First-generation high-potency antipsychotics: D₂antagonism → EPS
  • Second-generation antipsychotics: weaker D₂antagonism → fewer EPS

Neuroleptic malignant syndrome (NMS) ^[5]

• Description: life-threatening neurological disorder usually associated with antipsychotics that is characterized by a tetrad of features (fever, muscle rigidity, autonomic instability, and mental status changes) as well as rhabdomyolysis and elevated creatine kinase
• Etiology
  • Reaction to antipsychotic drugs (especially high-potency antipsychotics), other agents that affect the CNS (e.g., carbamazepine, lithium, venlafaxine), or certain antiemetics (e.g., metoclopramide, promethazine)
  • Genetic predisposition
  • A connection between NMS and the duration of therapy or therapeutic dose has not been established.
• Pathophysiology: The underlying mechanism is not well understood; disruption of numerous neurotransmitter pathways is suspected.
  • Central D₂ receptor blockade in the nigrostriatal pathway and hypothalamus, resulting in movement disorders and impaired thermoregulation
  • Increased sympathetic tone disrupts autonomic regulation and increases muscle tone and metabolism.
  • Increased release of calcium from the SR of striated muscle cells, resulting in increased contractility and muscle breakdown
• Clinical features: Onset usually occurs within 2 weeks of the first dose.
  • Muscle rigidity, akinesia, tremor
  • Hyperthermia
  • Autonomic instability (tachycardia, labile blood pressure, tachypnea, diaphoresis, dysrhythmias)
  • Mental status change: confusion, delirium, reduced vigilance, stupor
• Diagnostics
  • ↑↑ Creatine kinase
  • Leukocytosis
  • ↑ Transaminases
  • Metabolic acidosis
  • Myoglobinuria
  • Electrolyte abnormalities (hypocalcemia, hyperkalemia, hyponatremia or hypernatremia)
  • Low serum iron concentration
• Differential diagnosis
  • Lethal catatonia (see also catatonic dilemma )
  • See differential diagnosis of drug-induced hyperthermia.
• Treatment
  • Discontinuation of the antipsychotic drug!
  • Supportive measures (e.g., ICU care)
  • Pharmacotherapy
    • Dantrolene (ryanodine receptor antagonist): prevents the release of calcium from the sarcoplasmic reticulum of striated muscle → reduced muscle rigidity and hyperthermia
    • Alternatives: bromocriptine, apomorphine, or amantadine
    • Benzodiazepines can be administered to treat psychomotor agitation.

To remember the different symptoms of neuroleptic malignant syndrome, think "FALTER": Fever, Autonomic instability, Leukocytosis, Tremor, Elevated enzymes (creatine kinase, transaminases), Rigor

References:^{[4][5][6][7][8][9][10][11][12][13][14][15]}

We list the most important adverse effects. The selection is not exhaustive.

• All antipsychotics, with the exception of clozapine (used for treatment-resistant schizophrenia), have similar clinical effectiveness.
• The choice of drug depends on the side effect profile of the antipsychotic drugs and the patient's clinical status.
• SGAs are preferred in many cases because they carry a lower risk of EPS; however, in some patients (e.g., those with significant metabolic risk factors), FGAs may be more suitable.

To reduce/avoid anticholinergic side effects in patients of advanced age, high-potency substances (e.g., haloperidol, risperidone) or melperone are preferred!