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Pharmacology Of Psychiatric Drugs Notes

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

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

Metabolism
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Mostly by CYP450 hepatic enzymes

Excretion
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Mainly 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

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