6.3 Pharmacology Flashcards
Outline the pharmacological mechanism of antidepressants
- Exact mechanism not well understood
- Operates off monoamine theory of depression, so we aim to increase them
- BUT: actual effect takes 2-4 weeks, so there are obviously some other things at play…
What happens to adrenergic and serotonergic receptors in response to SNRI/SSRI use? How does this effect efficacy?
Density increases. Increases efficacy, since more serotonergic/noradrenergic transmission can occur.
Give some examples of SSRIs
- Citalopram
- Escitalopram
- Sertraline
- Fluoxetine
Give some examples of SNRIs
- Duloxetine
- Venlafaxine
- Desvenlafaxine
What are some contraindications for SSRIs/SNRIs?
- May precipitate mania in bipolar patients
- These drugs lower sodium; contraindicated for those with hyponatremia
(SS = Sodium Sucking)
What do we communicate to patients when prescribing SNRIs/SSRIs?
- Take a few weeks to become effective
- May experience other symptoms (better/worse), incl. adverse effects
What are some adverse effects of SSRIs?
- GI (nausea, diarrhoea, anorexia); get better with time
- Headaches
- Agitation, insomnia, tremor
- Sexual dysfunction (long term)
- Bleeding risk
SNRI adverse effects
- Same as SSRIs (sexual dysfunction, GI, agitation, insomnia, bleeding risk, headaches)
- Plus: palpitations, hypertension, orthostatic hypertension
Mechanism of tricyclic antidepressants
- Inhibit serotonin and noradrenaline reuptake
- BUT: also antagonise histamine receptors (sedation, weight gain), alpha adrenergic receptors (orthostatic hypotension), and muscarinic (anticholinergic effects)
What are the effects of tricyclic antidepressants on the heart?
- QT prolongation (depolarisation-repolarisation)
- Other effects on cardiac function
Effect of tricyclic antidepressants on seizure threshold
Decrease
Give some examples of tricyclic antidepressants
- Amitryptyline
- Dosulepin
- Doxepin
Tricyclic antidepressants contraindications
- Overdose risk
- Can precipitate manic episode
- Heart failure/LBBB
- Elderly
Adverse effects tricyclic antidepressants
- Sedation
- Cardiac effects
- Postural hypotension
- Muscarinic effects
- Anticholinergic effects
Depends on patient before you.
Mirtazapine mechanism
- Blocks post-synaptic serotonin 2 and 3 receptors
- Also acts on H1 receptors (which can help with sleep -> insomnia)
Contraindications for mirtazapine
- Bipolar disorder
- Serotonin-elevating drugs (serotonin syndrome)
Adverse effects of mirtazapine
- Sedation
- Increased appetite
What are some considerations when deprescribing antidepressants?
- Address underlying symptoms
- Watch for withdrawal effects
What are some SSRI withdrawal effects?
Dizziness, nausea, paraesthesia, anxiety, agitation, tremor, sweating
(Some of which are similar to initial causes…)
A patient has an inability to produce GABA. Should we give Alprazolam (AKA Xanax) for depression?
- No, you fool.
- They have no GABA; allosteric increase of GABA receptors is meaningless
Describe the mechanism of action of Benzos
- Allosterically bind to GABA receptors
- Increase GABAergic activity
- Hyperpolarises neurons, leading to widespread CNS depression
Give some examples of benzodiazepines
- Diazepam
- Oxazepam
- Nitrazepam
(-pam, -lam, -zam = probably benzo)
Benzodiazepine contraindications
- Existing CNS depression
- Liver failure
- Respiratory depression
- History of dependence
What do we communicate to patients when prescribing benzodiazepines?
- CNS sedation
- Effect on vision and driving
- Dependence/tolerance
- Anterograde amnesia (cannot form new memories)
Should you write a 6 month benzodiazepine script upon first encounter.
- No
- Not under any circumstances
- Absolutely not
Why do we want to deprescribe benzos ASAP?
- Fall risk
- Cognitive impairment
- Risk of withdrawal (seizures etc.)
How do we deprescribe benzodiazepines?
Need to provide treatment for underlying reason. (e.g. insomnia = sleep hygiene, anxiety = perhaps a psychologist or other coping strategies)
