Summary Points on Antipsychotic Drugs:
Classification of Antipsychotics: Typical (D2 blockers) and Atypical (acting via other mechanisms)
Actions of Typical Antipsychotics:
- Blocking D2 receptors with differing potency
- Sedative effects are more common in low-potency drugs
- Extrapyramidal symptoms more common in high-potency drugs
- Low anticholinergic and autonomic side effects in high-potency drugs
- Lower seizure threshold and potential to precipitate convulsions in epileptic patients
- Potent antiemetic drugs, except for thioridazine
- Significant α blocking and anticholinergic properties in low-potency drugs
- Can increase prolactin release resulting in galactorrhoea and amenorrhea
Actions of Atypical Antipsychotics:
- Antagonistic actions at 5-HT2 and alpha receptors
- May or may not possess D2 blocking activity
- Less likely to cause extrapyramidal symptoms
- Weight gain, hyperlipidemia, and new-onset diabetes mellitus are common side effects, except for ziprasidone and aripiprazole.
- Low incidence of extrapyramidal symptoms
- Interferes with male sexual function
- Can cause cardiac arrhythmia and retinal damage
- Trifluperazine, fluphenazine and haloperidol:
- High potency drugs
- Marked extrapyramidal symptoms
- Longest acting antipsychotic drug
- Selectively blocks D2 receptors
- Carries risk of arrhythmias due to QT prolongation
- Atypical antipsychotic drug
- Weak D2 blocking action
- Suppresses positive and negative symptoms of schizophrenia
- Risk of seizures and agranulocytosis
- Powerful anticholinergic effects
- Least risk of extrapyramidal symptoms
- Blocks 5-HT2, a adrenergic and D2 receptors
- More potent D2 blocker than clozapine
- Can cause extrapyramidal symptoms at high dose
- Risk of hyperprolactinemia
- Similar mode of action as risperidone
- Potent anticholinergic drug
- Can cause seizures and weight gain
- Associated with higher risk of stroke and death in elderly patients
- Causes QT prolongation
- No association with weight gain, hyperlipidemia or diabetes
- Can cause cataract formation
- Shortest half-life
- Used sublingually for schizophrenia and acute mania
- Brexipiprazole and cariprazine:
- New drugs approved for schizophrenia
- New atypical antipsychotic drug
- Indicated for oral treatment of hallucinations and delusions associated with Parkinson’s disease.
- Sedation: maximum with chlorpromazine, minimum with ziprasidone and aripiprazole
- Weight gain: all except haloperidol; less with ziprasidone
- Aggravation of seizures: more with clozapine, olanzapine, and chlorpromazine; less with risperidone and quetiapine
- Postural hypotension and inhibition of ejaculation: α-blocking property
- Retinal degeneration: thioridazine
- Agranulocytosis: clozapine
- Cataract formation: quetiapine
- Cholestatic jaundice: chlorpromazine
- Anticholinergic effects: dry mouth, blurred vision, constipation, urinary retention; maximum with thioridazine
- Hyperprolactinemia, amenorrhea, and galactorrhea: due to D2 blockade in the pituitary
- Extrapyramidal Symptoms (EPS): acute muscular dystonia, Parkinsonism, akathisia, malignant neuroleptic syndrome, tardive dyskinesia
- Acute mania and bipolar disorder
- Severe depression with psychotic features
- Alcoholic hallucinosis
- Gilles de la Tourette’s syndrome and Huntington’s disease
- Haloperidol and fluphenazine are potent typical antipsychotics, while risperidone is the most potent atypical antipsychotic.
- Clozapine, quetiapine, and aripiprazole have a negligible risk of extrapyramidal adverse effects.
- Chlorpromazine, thioridazine, and clozapine have the strongest anticholinergic activity.
- Fluphenazine (enanthate and decanoate) and haloperidol (decanoate) are long-acting injectable forms of typical antipsychotics, while risperidone and paliperidone are available in long-acting injectable form as atypical antipsychotics.
- Haloperidol is the most commonly used antipsychotic by intravenous route.
- Ziprasidone, aripiprazole, asenapine, and iloperidone have a negligible risk of causing metabolic adverse effects such as weight gain, hyperlipidemia, and new-onset diabetes mellitus.
- Asenapine, paliperidone, and ziprasidone have the greatest potential to prolong the QT interval.
Disclaimer: This article is for informational purposes only and should not be taken as medical advice. Always consult with a healthcare professional before making any decisions related to medication or treatment.