Antidepressants Flashcards by Jordan Cyr

What are the physiologic factors in depression?

changes in receptor-neurotransmitter relationships in the limbic area
-serotonin, norepinephrine, dopamine
-decrease in functional balance of these NTs

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What are the three mechanisms for alterations in the balance/function of neurotransmitters?

impaired synthesis of neurotransmitters
increased breakdown/metabolism of neurotransmitters
increased pump re-uptake of neurotransmitters

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What are the classes of antidepressants?

SSRI
SNRI
TCA
MAOI
atypical antidepressants

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What is the MOA of SSRIs?

inhibit SERT

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Which two SSRIs must be known for the exam?

escitalopram
citalopram

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What is the MOA of SNRIs?

inhibit SERT and NET

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Which SNRI must be known for the exam?

venlafaxine

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What is the MOA of TCAs?

inhibit SERT + NET + muscarinic receptors + a1 receptors + histamine receptors + Na+ channels
-also produce antiarrhythmic effects

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Which TCA must be known for the exam?

amitriptyline

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Which pump does desipramine prefer?

NET > SERT

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What is the MOA of MAOIs?

inhibit MAO which breaks down NTs

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Why are MAOIs last choice?

drug-drug interactions
drug-food interactions
-tyramine –> hypertensive crisis

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Which MAOI must be known for the exam?

isocarboxazid

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What is the feel good hormone?

dopamine
-released in cases of drug abuse or smoking

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What is the atypical antidepressant?

bupropion

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What is the MOA of bupropion?

inhibits DAT and NET

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What is another use of bupropion besides depression?

smoking

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What is bupropion toxicity associated with?

seizures and cardiac toxicity
-narrow therapeutic margin
-structurally similar to amphetamine

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Which antidepressant class is the safest?

SSRI
-fewer significant adverse effects and less problematic in overdose than TCAs and MAOIs
-more fatalities reported with extremely larger doses or co-ingestants like benzos or ethanol
-fatality is rare
-SNRIs like venlafaxine = greater risk of mortality in overdose

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Describe SSRI ADME.

absorption:
-tmax: 4-8h
distribution:
-PPB: 80-98%
-Vd: 10-40 L/kg
metabolism:
-CYP 2D6
elimination:
-t1/2: average of 15-35h
-numerous active metabolites
-mostly renally excreted

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What is the PPB of escitalopram?

56%

Which SSRIs are potentially more toxic in overdose?

citalopram and escitalopram
-dose dependent QT prolongation
-structurally different from other SSRIs

What is serotonin syndrome?

excessive levels of serotonin
-diaphoresis, diarrhea, hyperthermia, mental status change, myoclonus
-occurs most frequently after use of combination of serotonergic xenobiotics or high doses of isolated serotonergic xenobiotics

Which labs should be taken if experiencing SSRI toxicity?

ECG if citalopram, escitalopram, SSRI + co-ingestant
neuromuscular finding labs (CK, myoglobin, SCr)

What is the management of SSRI toxicity?

symptomatic and supportive care seizures: BZD cardiac abnormalities: sodium bicarbonate torsades de pointes: magnesium sulfate serotonin syndrome: cyprohepatidine

What is the MOA of sodium bicarbonate in SSRI toxicity?

increases in serum pH and extracellular sodium = increased electrochemical gradient across cardiac cell membranes

What is the MOA of magnesium sulfate?

decreases acetylcholine in motor nerve terminals and acts on myocardium = slowed rate of SA node impulse formation = prolonged conduction time

What is the MOA of cyprohepatidine?

competitive binding to serotonin receptor = cooling and treatment of muscular rigidity

What is the role of decontamination in SSRI toxicity?

? SDAC -most benefit within 1-2 h -may use up to 4 h no role for gastric lavage

What is the role of elimination in SSRI toxicity?

no role for MDAC -no role due to rapid absorption no role for hemodialysis -ineffective due to high PPB, Vd

What is the key to successful management in TCA toxicity?

early identification -hard to distinguish serious toxicity based on symptoms alone -progression of clinical toxicity is unpredictable and may be rapid -get an ECG!

Describe TCA absorption.

well absorbed tmax up to 12h in overdose anticholinergic effect on gastric emptying =delay emptying

Describe TCA distribution.

highly lipophilic and widely distributed -Vd = 10-50 L/kg PPB: 85-98% (highly protein bound) not a good candidate for hemodialysis

How are TCAs metabolized?

multiple CYPs metabolism is highly variable

Why is TCA metabolism highly variable?

genetic polymorphisms in 2D6 influenced by concomitant ingestion of ethanol or coingestants that induce or inhibit 2D6

What is a poor predictor of outcome in TCA toxicity?

dose ingested and plasma concentration

What is essential with TCA toxicity?

early ECG

Which symptoms of TCA toxicity show rapid progression?

cardiotoxic symptoms -onset often within 2 hours of ingestion

What is the main mechanism of TCA causing cardiotoxicity?

Na+ channel blocking = QRS prolongation

Which body systems are impacted by TCA toxicity?

cardio respiratory CNS

How is the severity of TCA toxicity best reflected?

by ECG, not serum levels

At what point does the QRS show risk of cardiotoxicity?

> 100 ms

What is the first line management for dysrhythmias caused by TCAs?

sodium bicarbonate

What is the MOA of sodium bicarbonate for dysrhythmias caused by TCAs?

sodium load: helps overcome Na+ channel blockade alkalinization of arterial blood pH: inhibits binding of TCA to myocardial Na+ channel as drug is not ionised *benefit due to increased pH and increased sodium*

What is the standard of care for TCA poisoning?

sodium bicarbonate

What is the treatment if dysrhythmias continue from TCA poisoning despite sodium bicarbonate?

lidocaine -blocker of Na+ and K+ channels hypertonic saline magnesium sulfate

Which drugs should not be given during dysrhythmias from TCAs?

class IA or IC antiarrhythmics beta blockers physostigmine and type 3 anti-dysrhythmic agents flumazenil

What is the management of seizures caused by TCA toxicity?

benzodiazepines sodium bicarbonate may also help manage/prevent seizures if QRS complex is shortened

What is the role of decontamination in TCA toxicity?

?/maybe gastric lavage -reasonable in adults with intentional OD -risk of aspiration SDAC -binds -risk of aspiration

What is the role of elimination in TCA toxicity?

maybe MDAC no hemodialysis -PPB, lipophilic, Vd

What is the antidote for TCA toxicity?

intravenous lipid emulsion -hemodynamically unstable patients or those in cardiac arrest unresponsive to conventional therapy -also in patients where bicarbonate is not effective