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Understanding Na Channel Blockers in Toxicology

Explore the classification, mechanisms, and management of Na channel blockers toxicity. Learn about Class 1 anti-dysrhythmics, TCA's, propoxyphene, SSRI’s, neuroleptics, and more. Understand EKG findings and different antidysrhythmic drugs.

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Understanding Na Channel Blockers in Toxicology

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  1. Toxicology 6:Na Channel Blockers Thanks to: P. Ukrainetz S. McPherson

  2. Outline • Na Channel Blockers • Class 1 anti-dysrhythmics • TCA’s • Propoxyphene • Other Pharmacology • SSRI’s • Neuroleptics

  3. What we won’t cover • Cocaine • Local anesthetics • Pufferfish

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

  5. The Sodium Channel • Voltage gated • 3 phases • Slow and fast

  6. Action Potential

  7. Action Potential

  8. Increased automaticity Triggered activity Re-entry with unidirectional block Tachyarrhythmias

  9. Anti-dysrhythmics Board Work

  10. EKG findings

  11. DDx wide qrs Class 1a Class 1c Cyclic anti-depressants Propoxyphene Cocaine Local anesthetics

  12. Procainamide Disopyramide Quinidine Class 1a

  13. Class 1a

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

  15. Procainamide • NAPA • ACLS: indications? • Dosing?

  16. Manamement of OD • ABC’s, monitor • EKG • HCO3 if wide qrs* • Consider Ca, glucagon • Lidocaine for dysrhythmias • TdP: Mg, pacing • AVOID: 1c/1a, BB, CCB

  17. Lidocaine Tocainide Mexiletine Phenytoin Class 1b

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

  19. Management • Basic resuscitation as in Ia • “Non-responsive” bradycardia’s • Charcoal

  20. Flecainide Propafenone Class 1c

  21. Flecainide • Oral, IV • PR/QRS without QT • Increase mortality in cardiac pt’s • Primary use: outpt. afib

  22. Management • Basic resuscitation • HCO3 • Amiodarone • Avoid other 1a/1c

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

  24. Does it matter which TCA?

  25. TCA’s By what mechanisms do TCA’s exert their effects?

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

  27. Bottom Line: Unpredictable

  28. How much matters?

  29. 1 gram

  30. IV, O2, Monitor Vitals Case continued

  31. Most likely rhythm?

  32. What else is expected on physical?

  33. “Belladonna”

  34. TCA “Copy Cats”

  35. First Test?

  36. EKG

  37. EKG • Three benefits: • Diagnosis • Prognosis • Effect of treatment

  38. Prognosis and EKG • QRS duration • Terminal 40ms • aVR findings

  39. 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

  40. Who wants a TCA Level?

  41. Bottom Line: Does not correlate with toxicity Does not predict complications

  42. Management? Case Continued

  43. “Nearly all cases” PHAILS 1mg/kg Consider MDAC Charcoal?

  44. Life-threatening Non-absorbable No antidote Early Gastric Lavage

  45. Potentially toxic SR preparation Non-absorbable and no other method of decontamination Removal of Packets Whole Bowel Irrigation

  46. NOT EFFECTIVE Elimination Urinary Alkalinization Dialysis

  47. HCO3 - • Mainstay of therapy • 1-2meq/kg • Q3-5 min boluses • +/- infusion

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