MEDI7111 Lecture Notes - Lecture 5: Heme, Haloperidol, Agranulocytosis
Anti-Psychotic Medications
Antipsychotic drugs fall into two general categories; older typical drugs and newer atypical
drugs. These drugs are not a cure, most patients with schizophrenia will need lifelong treatment
to manage remission. It is preferable to prevent psychotic episodes than to treat them.
Due to the difficulty in maintaining compliance to treatment regimes, often weekly IM depot
administration of the drugs can be used to improve outcomes, with a transition to oral
medications once the patient is stable & the doctor is happy with compliance.
All antipsychotic medications act on a variety of receptors with varying therapeutic and adverse
effects. The D2 receptor is the most recognised site of action; 60-75% inhibition of the D2
receptor is required for therapeutic effects while blockade of >78% causes EPS side effects.
Mechanism of Action Therapeutic Effects Adverse Effects
α-1 antagonist N/A Dizziness
Orthostatic hypotension
Reflex tachycardia
D2 antagonist Alleviation of positive
symptoms of schizophrenia
EPS
serum prolactin levels ↑
D4 antagonist Alleviation of negative
symptoms of schizophrenia
EPS ↓
N/A
H1 antagonist Sedation* Drowsiness
appetite & weight ↑
Muscarinic antagonist N/A Blurred vision
Constipation
Dry mouth
Urinary retention
5-HT2 antagonist Alleviation of negative
symptoms of schizophrenia
EPS↓
Anxiety
Insomnia
Typical Antipsychotics
As the MOA of typical anti-psychotics is dopamine antagonism, extrapyramidal symptoms (EPS)
are seen in 40-50% of patients. These include acute dystonia (severe muscle spasms),
Parkinsonism, akathisia (inability to remain still, trouble sleeping) and tardive dyskinesia
(repetitive involuntary movements – after chronic use). Additionally, excessive blocking of D2
receptors can lead to inhibition of reward pathways and anhedonia.
Drug MOA Clinical Features Side Effects
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Antipsychotic drugs fall into two general categories; older typical drugs and newer atypical drugs. These drugs are not a cure, most patients with schizophrenia will need lifelong treatment to manage remission. It is preferable to prevent psychotic episodes than to treat them. All antipsychotic medications act on a variety of receptors with varying therapeutic and adverse effects. The d2 receptor is the most recognised site of action; 60-75% inhibition of the d2 receptor is required for therapeutic effects while blockade of >78% causes eps side effects. As the moa of typical anti-psychotics is dopamine antagonism, extrapyramidal symptoms (eps) are seen in 40-50% of patients. Parkinsonism, akathisia (inability to remain still, trouble sleeping) and tardive dyskinesia (repetitive involuntary movements after chronic use). Additionally, excessive blocking of d2 receptors can lead to inhibition of reward pathways and anhedonia. 50x more potent than chlorpromazine for d2 antagonism. Most of the side effects listed in table above.
