K2iv / 21B16: Classify the anti-psychotic drugs (25%).  Outline the pharmacology of haloperidol (75% marks)

21B16: Exam Report

Classify the anti-psychotic drugs (25%).  Outline the pharmacology of haloperidol (75% marks)

28% of candidates passed this question.

Excellent answers were able to provide a classification of antipsychotics based on either typical/atypical or first/second generation categories, provide examples of each and identify key differences in mechanism and effects. They also distinguished between butyrophenones and phenothiazines within the typical antipsychotic group. Haloperidol was identified as a butyrophenone, with description of pharmaceutics, dose and route, as well as pharmacodynamics and pharmacokinetics. Key adverse effects were detailed, focusing on those specific to haloperidol, including a description of different types of extrapyramidal symptoms and QT prolongation/ torsades de pointes.

K2iv / 21B16: Classify the anti-psychotic drugs (25%).  Outline the pharmacology of haloperidol (75% marks)

Classification of antipsychotics:

Typical( 1st generation)

Further subdivided into:

  • Butyrophenones (eg haloperidol)
  • Phenothiazines ( eg chlorpromazine)
  • Thioxanthene ( flupenthixole)
  • MOA: more potent D2R antagonist, moderate antagonism of 5 HT2 receptor and alpha adrenoreceptor. Weakly inhibit mAChR and H1R
  • Effect – Ameliorate +ve symptoms only (little effect on –ve symptoms)
  • Greater incidence of EPS

Atypical (2nd generation)

  • Diazepines (Eg. Clozapine, Olanzapine)
  • Dibenzothiazepines (Eg. Quetiapine)
  • Benzamides (Eg. Sulpiride)
  • Benzisoxazols (Eg. Respirdone)
  • Highly selective D2R antagonist, high affinity for 5 HT2R and moderate affinity for alpha adrenoreceptor.
  • Have greater therapeutic efficacy (ameliorate both +ve and –ve symptoms)
  • Fewer side effects than typical agents (esp movement disorders and gynaecomastia)
  • Indicated for treatment resistance or side-effects with typical agents (esp extrapyramidal symptoms)

Haloperidol (1st generation)


N& V, Delirium

Others: Schizophrenia, tics, premedication, palliative care

Phamaceutics (Chemical)

Butyrophenone derivative. Tablet, capsule, syrup, clear solution 5mg/ml of haloperidol

Pharmacodynamics - Antiemetic, Neuroleptic


  1. Post synaptic GABA antagonism
  2. Central dopaminergic D2 blockade, leading to increased threshold for vomiting @ CTZ


CVS: minimal CVS, antagonistic effect at alpha adrenergic receptor may lead to hypotension in presence of hypovolaemia

Resp:  min effect

CNS: neurolepsis ( state of diminished motor activity, anxiolysis, indifferent to surrounding). Seizure threshold is raised

GI: powerful antiemetic

Met: hyperprolactinemia


Dose 1-15mg PO, IV 1-5mg. Longer duration than droperidol


Well absorbed. Bioavail 50-88%


92% PB

Vd 18-30L/kg


Liver – extensive metabolism a reduced metabolite may be active



Half Life

10-38hr, depending on route of administrationx

Adverse Drug Reactions


  • Extrapyramidal Symptoms ( incl neuroleptic malignant syndrome – catatonia, CVS lability, hyperthermia, myoglobinemia. Mortality 10%). GI and haematopoietic disturbance, affect LFT.
  • Prolongs QT/torsades de pointes



  • Hypotension result from haloperidol should not be treated with adrenaline, as futher decrease in BP may result
  • Not removed with HD
  • Increase risk of stroke and death if taken in higher dose ( esp haloperidol)

Author: Huiling Tan