Toxicology 6: Na Channel Blockers

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Toxicology 6Na Channel Blockers

• Thanks to P. Ukrainetz
• S. McPherson

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Outline

• Na Channel Blockers
• Class 1 anti-dysrhythmics
• TCAs
• Propoxyphene
• Other Pharmacology
• SSRIs
• Neuroleptics

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What we wont cover

• Cocaine
• Local anesthetics
• Pufferfish

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Antidysrhythmics

• Classification
• Class 1 Na Channel Blockers
• Class 2 Beta Blockers
• Class 3 K Channel Blockers
• Class 4 Ca Channel Blockers
• Class 5 Other

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The Sodium Channel

• Voltage gated
• 3 phases
• Slow and fast

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Action Potential
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Action Potential
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Tachyarrhythmias

• Increased automaticity
• Triggered activity
• Re-entry with unidirectional block

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Anti-dysrhythmics

• Board Work

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EKG findings
PR QRS QTc
1a 0 Inc Inc
1b 0 0 0 or Dec.
1c Inc. Inc 0 or Inc.
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DDx wide qrs

• Class 1a
• Class 1c
• Cyclic anti-depressants
• Propoxyphene
• Cocaine
• Local anesthetics

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Class 1a

• Procainamide
• Disopyramide
• Quinidine

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Class 1a
Anti-cholinergic QTc Hypotension/- inotropy
Quinidine
Procainamide -
Disopyramide
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Procainamide

• IV, IM, or PO
• Renally excreted
• 1/3 lupus-like syndrome

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Procainamide

• NAPA
• ACLS indications?
• Dosing?

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Manamement of OD

• ABCs, monitor
• EKG
• HCO3 if wide qrs
• Consider Ca, glucagon
• Lidocaine for dysrhythmias
• TdP Mg, pacing
• AVOID 1c/1a, BB, CCB

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Class 1b

• Lidocaine
• Tocainide
• Mexiletine
• Phenytoin

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Lidocaine

• CNS, cardiac, and GI toxicity
• Usually mild, dose-dependant
• Low pro-arrhythmia risk?
• ACLS Indications? Dosing?

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Management

• Basic resuscitation as in Ia
• Non-responsive bradycardias
• Charcoal

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Class 1c

• Flecainide
• Propafenone

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Flecainide

• Oral, IV
• PR/QRS without QT
• Increase mortality in cardiac pts
• Primary use outpt. afib

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Management

• Basic resuscitation
• HCO3
• Amiodarone
• Avoid other 1a/1c

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TCAs

• Pt. called 9-1-1 after overdose
• Empty bottle of TCA on scene
• Normal strip. Stable

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Does it matter which TCA?
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TCAs

• By what mechanisms do TCAs exert their effects?

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Mechanisms

• Na channel blockade
• K channel blockade
• Gaba antagonism
• Amine re-uptake inhibitor
• Anticholinergic
• Alpha-blocker

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• Bottom Line
• Unpredictable

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How much matters?
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• 1 gram

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Case continued

• IV, O2, Monitor
• Vitals

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• Most likely rhythm?

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• What else is expected on physical?

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Belladonna
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TCA Copy Cats
Sz, QRS, anti-chol Sz, QRS
Carbamazepine propanolol
Phenothiazines Class 1c
Anti-histamine cocaine
Class 1as Local anesthetics
Cyclobenzaprine lithium
propoxyphene
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• First Test?

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• EKG

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EKG

• Three benefits
• Diagnosis
• Prognosis
• Effect of treatment

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Prognosis and EKG

• QRS duration
• Terminal 40ms
• aVR findings

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Bottom Line

• Useful to consider these measurements
• -not 100 sensitive
• -useful if absent (to confirm lack of cardiac
  toxicity)
• -serial ECGs
• -do not use in isolation

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• Who wants a TCA Level?

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• Bottom Line
• Does not correlate with toxicity
• Does not predict complications

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Case Continued

• Management?

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Charcoal?

• Nearly all cases
• PHAILS
• 1mg/kg
• Consider MDAC

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Gastric Lavage

• Life-threatening
• Non-absorbable
• No antidote
• Early

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Whole Bowel Irrigation

• Potentially toxic SR preparation
• Non-absorbable and no other method of
  decontamination
• Removal of Packets

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Elimination

• Urinary Alkalinization
• Dialysis

• NOT EFFECTIVE

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HCO3 -

• Mainstay of therapy
• 1-2meq/kg
• Q3-5 min boluses
• /- infusion

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Dysrhythmias

• HCO3
• Lidocaine
• Other Mg, phenytoin,

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Hypotension

• Volume
• HCO3
• Pressor of choice?
• ECMO

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Pressors
a B Dopamine
Phenylephrine - -
Dopamine
Dobutamine - -
Epinephrine -
Norepinephrine -
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Seizures

• Usually brief
• 1st line benzos
• 2nd line phenobarbitol or propofol
• 3rd line? Paralysis, general anesthesia, EEG

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Admission

• Asymptomatic for 6 hours
• No ECG changes (except tachycardia)
• Then, can be discharged home
• Otherwise, need admission

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Propoxyphene
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What is it used for?

• Now, nothing
• Mild/moderate pain relief
• Restless leg syndrome
• Opioid withdrawal

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Pharmacology

• Structural analog of methadone
• In Overdose, Na channel blocking
• Often formulated with acetaminophen or ASA

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Treatment

• HCO3
• Lidocaine
• Naloxone?
• Benzodiazepines

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THE END