Summary of Typical antipsychotics
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Transcript for Typical antipsychotics
Antipsychotics, as their name implies, are mainly used to treat schizophrenia and other psychotic conditions.
Even though the exact cause of schizophrenia is still unknown, there's some evidence that suggests it’s related to altered levels of the neurotransmitter dopamine.
Alright, within the brain, dopamine is found in 4 main dopamine pathways: the mesolimbic pathway, which controls motivation and desire; the mesocortical pathway, which helps regulate emotions; the nigrostriatal pathway, which contains motor neurons that bypass the medullary pyramids, to control involuntary movements and coordination; and lastly, the tuberoinfundibular pathway, which releases dopamine to limit the secretion of prolactin.
Other regions of the central nervous system that are rich in dopamine receptors include the chemoreceptor trigger zone, which initiates the vomiting reflex, and the medullary periventricular pathway, which regulates eating behavior.
However, in schizophrenia, altered levels of dopamine mainly affect the mesolimbic pathway and mesocortical pathway.
There’s usually high levels of dopamine in the mesolimbic pathway which causes positive symptoms of schizophrenia, such as delusions, hallucinations, and disorganized thought.
On the other hand, low levels of dopamine in the mesocortical pathway cause negative symptoms of schizophrenia, such as lack of motivation, social withdrawal, and “flat affect,” which basically means a lack of emotions.
When it comes to treating schizophrenia, some typical antipsychotics like haloperidol, trifluoperazine, and fluphenazine have a higher potency, which means you need less of it to achieve a therapeutic effect.
Now, in conditions such as schizophrenia, typical antipsychotics block dopamine D2 receptors in the mesolimbic pathway, thereby alleviating positive symptoms of schizophrenia.
However, they also block dopamine receptors in the mesocortical pathway, which might actually worsen the negative symptoms.
Aside from their use in psychiatric disorders, blocking dopamine receptors in the chemoreceptor trigger zone can also decrease nausea and vomiting, while blocking histamine H1 receptors can have an antipruritic and sedative effect.
Alright, moving on to side effects. In the tuberoinfundibular pathway, they inhibit the release of prolactin, causing oligomenorrhea, galactorrhea, and gynecomastia; and lastly, in the nigrostriatal pathway, which contains motor neurons that bypass the pyramids of the medulla, they cause extrapyramidal symptoms, which usually involve abnormal movements.
Let’s start with dystonia, which may occur within a few hours to days of treatment, and includes muscle spasms of the tongue, face, neck, and back.
It also causes oculogyric crisis, which is a spasm of the extraocular muscles, causing an upward and outward position of the eyes.
After a few days to a month, there could be Akathisia or pseudoparkinsonism.
Akathisia is characterized by restlessness and an urge to move the limbs.
Pseudoparkinsonism is characterized by muscle rigidity, usually in the facial muscles, giving the face a wooden, mask-like appearance.
Other symptoms include bradykinesia, (or slow movements), and tremors.
It’s important to note that typical antipsychotics are more likely to cause these side effects compared to the atypical antipsychotics.
However, extrapyramidal symptoms usually disappear once the medication is stopped.
Now, moving on to tardive dyskinesia, which can present after several months or even years; is characterized by constant involuntary, rhythmic movements.
This typically happen with the perioral muscles causing the person to repeatedly smack, or purse their lips.
Unlike acute extrapyramidal symptoms, tardive dyskinesia can be irreversible, so the medication should be discontinued at the first sign of tardive dyskinesia.
Now, the most dangerous and severe extrapyramidal side effect is neuroleptic malignant syndrome or NMS, which typically starts days to weeks after starting the medications.
It’s characterized by confusion, coma, agitation, muscle rigidity, seizures, and hyperthermia.
These symptoms are almost identical to serotonin syndrome, caused by antidepressants like selective serotonin reuptake inhibitors.
However, serotonin syndrome causes hyperreflexia and dilated pupils, while in neuroleptic malignant syndrome there’s hyporeflexia and normal pupils.
If this condition progresses, it will cause rhabdomyolysis, where the muscles break down.
Finally, typical antipsychotics also cause side effects by blocking other receptors: Alpha-1 receptor inhibition causes orthostatic hypotension; muscarinic receptor inhibition causes anticholinergic, or atropine-like side effects such as dry mouth, blurred vision, urinary retention, and constipation; and histamine H1 receptor inhibition causes sedation.