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Pharmacology Of Psychiatric Drugs Notes

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This is an extract of our Pharmacology Of Psychiatric Drugs document, which we sell as part of our Psychiatry Notes collection written by the top tier of University Of Leicester students.

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Psychiatric Drugs AdministrationMostly oral (so undergo 1st pass metabolism) IV/IM used in emergencies or in those who can't maintain on oral dose

DistributionMostly lipid soluble so can cross the BBB Therefore all excreted in breast milk

MetabolismMostly by CYP450 hepatic enzymes

ExcretionMainly renal NB - Lithium is not metabolized, just renally excreted - risk of toxicity with renal disease

Mechanism of action
- Affect neurotransmitters such as

Excitatory neurotransmitters (dopamine, NA, 5-HT, glutamine)

Inhibitory neurotransmitters (GABA, glycine)

Drugs act to modulate action potentials by affecting reuptake, breakdown and receptors of these neurotransmitters

Antidepressants 1

Selective Serotonin Reuptake Inhibitors (SSRI) Fluoxetine, citalopram, sertraline Specific inhibition of 5-HT reuptake FIRST LINE for moderate to severe depression Also used for anxiety disorders (especially OCD)
- 2-4 weeks before they begin to have an effect
- Safe if taken alone in overdose
- Side effects include o Nausea, vomiting, diarrhea o Agitation, insomnia o Anorgasmia o Increase suicide risk in those <18yrs

May cause 'serotonin syndrome' (body response to too much serotonin)
- Tremor
- Hypothermia
- Cardiovascular collapse

Serotonin Noradrenaline Reuptake Inhibitors (SSNRIs)

Venlafaxine ADRs - Nausea/vomiting, diarrhea, dry mouth, hyponatraemia Short T1/2 (withdrawal syndrome)

Tricyclic Antidepressants (TCAs)

Amitriptyline, imipramine, Lower doses = neuropathic clomipramine pain Block reuptake of serotonin and NA Higher doses =
Also act on
- H1 receptors = sedation effects
- A1 receptors
- Muscarinic receptors = anticholinergic effects e.g dry mouth, blurred vision, constipation, urinary retention Onset of action = 4 weeks Other side effects
- Initially o Sedation, confusion and motor impairment o Usually wears off after 2 weeks
- Long term o Drowsiness, poor concentration, postural hypotension
- Overdose o Initial euphoria o Delerium, convulsions, respiratory depression, coma o Severe anticholinergic effects o NA block Cardiac toxicity o Prolonged QT syndrome, ventricular arrhythmias Potentiates the effects of alcohol and anaesthetics (respiratory depression) Interferes with anti-hypertensives Slow elimination especially in elderly

2

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