Drug Classification: Antipsychotics

Lithium

UNDER REVIEW (September 2016)

Mechanism of Action:

Lithium is a positively charged element or particle that is similar to sodium and potassium. It interferes at several places inside cells and on the cell surface with other positively charged atoms such as sodium, potassium, calcium, and magnesium which are important in many cellular functions. Lithium interferes with the synthesis and reuptake of chemical messengers by which nerves communicate with each other (neurotransmitters). Lithium also affects the concentrations of tryptophan and serotonin in the brain. In addition, lithium increases the production of white blood cells in the bone marrow. Lithium’s effects usually begin within one week of starting treatment, and the full effect is seen by 2 to 3 weeks. Precise mechanism of action in bipolar depression is not understood – possibly interference with inositol trisphosphate formation, or with cAMP formation.

 

Olanzapine

UNDER REVIEW (September 2016)

Mechanism of Action:

Olanzapine is a thienobenzodiazepine, one of the ‘atypical’ antipsychotic drugs. Olanzapine has a high affinity for dopamine and serotonin (5-HT) receptors. Like most atypical antipsychotics compared to the older typical ones, it has a lower affinity for histamine, cholinergic muscarinic and alpha adrenergic receptors. The mechanism of action of olanzapine is unknown but the antipsychotic activity is probably mediated primarily by antagonism at dopamine D2 receptors. Serotonin antagonism may also play a role in the effectiveness of olanzapine, but the significance of 5-HT2A antagonism is debated. Antagonism at muscarinic cholinoceptors, histamine receptors and alpha adrenoceptors may explain some of the side effects of olanzapine, such as anticholinergic effects, weight gain, sedation and orthostatic hypotension.

Lecture and CAL materials:

Haloperidol

UNDER REVIEW (September 2016)

Mechanism of Action:

An example of the butyrophenone group of “typical” antipsychotic drugs. Predominant action is as a dopamine D2-receptor antagonist, but also block other receptors such as serotonin (5-HT) receptors. The action at dopamine ors give rise to the extrapyramidal effects (Parkinsonian movement disorder, dystonic movements and tardive dyskinesia), and also to hyperprolactinaemia.

Lecture and CAL materials:

Chlorpromazine

UNDER REVIEW (September 2016)

Mechanism of Action:

The best example of the phenothiazine group of “typical” antipsychotic drugs. Predominant action is as a dopamine D2-receptor antagonist, but also block other receptors (D3, alpha-1 adrenoceptor, histamine H1-receptors, muscarinic ACh receptors and serotonin (5-HT) receptors. This broad pharmacological profile also offers the potential for multiple unwanted effects. The best known result from blocking dopamine D2 receptors, which may give rise to the extrapyramidal effects (Parkinsonian movement disorder, dystonic movements and tardive dyskinesia), and also to hyperprolactinaemia.

Lecture and CAL materials: