Session 11 - Pharmacology in Psychiatry Flashcards
Common receptor effects of muscarinic (acetylcholine) receptors.
- dry mouth
- difficulty swallowing
- thirst
- difficulty urinating
- urinary retention
- hot and flushed skin
- dry skin
Common receptor effects of histamine receptors.
- dry mouth
- drowsiness
- dizziness
- nausea and vomiting
Common receptor effects of adrenergic / noradrenergic receptors.
- sweating
- tremor
- headaches
- nausea
- dizziness
Generally, how long does it take for antidepressants to begin to work?
Two to three weeks.
Types of antidepressants.
- SSRIs (most common)
- SNRIs
- Mirtazapine
- Tricyclic antidepressants
- MAOIs
MOA of SSRIs.
Increase serotonin activity by reducing the presynaptic uptake of serotonin after release, therefore more serotonin sits in the synapse.
This leads to a down-regulation of post-synaptic receptors within 2-3 weeks.
Common side-effects of SSRIs.
- restlessness and agitation on initiation
- nausea
- GI disturbance
- headache
- weight loss / gain
- sexual dysfunction
- bleeding
- suicidal ideation
How can the specific side effects of SSRIs be managed?
a) restlessness and agitation on initiation
b) sexual dysfunction
c) bleeding
d) suicidal ideation
a) judicious use of benzodiazepines on initiation
b) prescribe viagra to help achieve erection
c) co-prescribe PPI if risk factors for bleeding
d) repeat consultation after 2-3 weeks to quantify suicide risk
Dosage of Sertraline (SSRI).
50-200mgs
Safest in cardiac disease.
Dosage of Citalopram (SSRI).
20-40mgs
Dosage of Escitalopram (SSRI).
10-20mgs
Dosage of Fluoxetine (SSRI).
20-60mgs
Dosage of Paroxetine (SSRI).
20-60mgs
Why should an ECG be conducted when prescribing Citalopram or Escitalopram for a patient?
Risk of QTc prolongation and subsequent arrhythmias.
MOA of SNRIs.
Increase serotonin and noradrenaline activity by reducing the presynaptic uptake of serotonin and noradrenaline after release, therefore more serotonin and noradrenaline sits in the synapse.
This leads to a down-regulation of post-synaptic receptors within 2-3 weeks.
Side effects of SNRIs.
Similar side effects to SSRIs, but greater potential for:
- sedation
- nausea
- sexual dysfunction
- weight gain
Other side effects are similar to SSRIs:
- restlessness and agitation on initiation
- GI disturbance
- headache
- bleeding
- suicidal ideation
Dosage of Duloxetine.
60-120mgs
Low dose range.
Dosage of Venlafaxine.
75-375mgs
Greater efficacy than Duloxetine and can go to a higher dose.
Monitoring required at higher Venlafaxine dosing.
Venlafaxine >225mgs cautioned in heart disease - monitor blood pressure.
MOA of Mirtazapine.
Antagonises 5HT-2 and 5HT-3 receptors.
Agonises H1 receptors, causing sedation as side effect.
Side effects are used to a therapeutic advantage.
Side effects of Mirtazapine.
- sedation
- weight gain
Side effects are pronounced even at low doses, therefore a reduction in dose would not help relieve symptoms.
MOA of tricyclics.
Agonise muscarinic and histaminergic receptors, causing sedation.
Can also be used to treat neuropathic pain.
Examples of tricyclics.
Newer tricyclics:
- lofepramine
- nortriptyline
tolerated better than older tricyclics:
- amitriptyline
Risk of tricyclics.
Can be fatal in overdose - cause QTc prolongation and arrhythmias.
MOA of MAOIs.
Inhibit monoamine oxidase, having effects on serotonin, dopamine and adrenaline levels.
Some are irreversible (more dangerous), while some are reversible (less dangerous).
Interactions of MAOIs.
Potential for significant and dangerous interaction with other drugs.
Rarely prescribed.
What foods need to be avoided if prescribing MAOIs?
Avoid tyramine products:
- cheese
- pickled meats
- wine
Potential for tyramine reaction leading to hypertensive crisis.
MOA of Vortioxetine.
Differing effects on serotonergic activity according to receptor.
Side effects of Vortioxetine.
Generally well tolerated.
Most common side effect is nausea.
What factors influence antidepressant choice?
- what has been used before?
- what has been effective before?
- what has been well tolerated before?
- what does the patient want?
- are there any particular symptoms or comorbidities you want to address?
General antidepressant step-up.
- Sertraline
- Different SSRI
- SNRI / Mirtazapine
If SSRI causes major weight changes or sleep difficulty consider Mirtazipine; if comorbid neuropathic pain consider SNRI first line.
When should you switch antidepressant medication?
Switch if no treatment effect within the first 4 weeks.
When should you increase the dose of antidepressant medication?
If there has been partial benefit within the first 4 weeks.
What is discontinuation syndrome?
For some people, the rapid exit of serotonin from the system can cause an unpleasant syndrome.
FIRM STOP:
Flu like Sx
Insomnia
Restlessness
Mood swings
Sweating
Tummy problems (pain, cramps, D+V)
Off balance
Parasthaesia
Is discontinuation syndrome life-threatening?
No - it is unpleasant but not life-threatening.
Which antidepressants are particularly associated with discontinuation syndrome?
Those with a short half life:
- Venlafaxine
- Paroxetine
How can the risk of discontinuation syndrome be reduced?
- alternate days of taking
- snap tablets in half
- switch to Fluoxetine* (long half life) then reduce
*Fluoxetine comes in liquid preparation so can make micro-adjustments in dose.
What is serotonin syndrome?
A potentially life-threatening side effect of antidepressants, characterised by excess serotonin.
Presentation of serotonin syndrome:
a) cognitive
b) autonomic
c) somatic
a) headaches; agitation; hypomania; confusions; coma
b) shivering; sweating; hyperthermia; tachycardia; nausea and diarrhoea
c) myoclonus; hyper-reflexia; tremor
Can cause seizures and sudden death.