TCA and Digoxin toxicity

Question 1

3 mechanisms of HCO3 in TCA toxicity

Answer 1

1. Raises serum pH (decreases proportion of unbound active drug available)
2. increases myocardial contractility
3. delivers Na ions to cardiac myocytes (overcomes drug induced sodium channel blockade)

Question 2

TCA Metabolic pathway and T1/2 life

Answer 2

Hepatic metabolism via cytochrome P450
T1/2=1-3d

Question 3

7 TCA receptors

Answer 3

Na
K
Serotonin/dopamine (5HT/dopamine)
Histamine
anti-alpha 1
anti-Gaba
muscarinic (cholinergic)

Question 4

3 electrolyte abnormalities associated with Digoxin toxicity

Answer 4

1. Hypokalemia (chronic toxicity)
   -treat with slow K replacement
2. Hyperkalemia (acute)
   -treat with antidote Digibind
3. Hypomagnesemia

Question 5

4 cardiac arrhythmia’s with

Answer 5

1. Bidirectional VT
2. slow afib w/ complete HB (any AV block)
3. New bigeminy
4. Junctional tachycardia

Question 6

3 mechanisms of action of digoxin

Answer 6

1. inhibits Na/K+ ATPase pump (increase intracellular Ca–>increases inotropy)
2. decreases SA depolarizing and AV conduction
3. increases myocardial automaticity and repolarization

Question 7

Digoxin toxicity antidote

Question 8

3 cuases of hypotension in TCA toxicity

Answer 8

1. alpha 1 blockade -hypotension
2. severe acidosis
3. CV compromise (Na channek blockade)

Question 9

ECG findings of TCA toxicity

Answer 9

1.QRS >100ms
2. terminal 40ms RAD (a. Tall R in aVR, R:S ratio in aVR >0.7)
–>PPV 66-81% TCA poisoning

Question 10

5 clinical signs of TCA toxicity

Answer 10

1. AMS
2. Hypotension
3. Cardiac dysrhythmias
4. Seizures
5. Hot and crazy (cholinergic effects)

Question 11

Toxic dose for most TCAs

Answer 11

5 mg/kg
less for some –>nortryptiline, dothepin, doxepin, desipramine
1 pill can kill in peds

Question 12

Utility of HD in TCA toxicity

Answer 12

Large volume of distribution protein binding, large molecules –> therefor not helpful.

Question 13

5 2nd/3rd line agents for TCA toxicity

Answer 13

1. Hypertonic saline 1-2cc/kg
2. benzos -seizure control
3. Magnesium - arrhythmia
4. Pressors
5. intralipid 1-1.5 cc/kg IV bolus
6. lidocaine (class IIb—>arrythmia control)

Question 14

2 treatment goals in TCA toxicity

Answer 14

1. Narrow QRS <100ms
2. serum pH 7.45-7.55

Question 15

When to consider activated charcoal in TCA toxicity

Answer 15

acute life threatening ingestions within 1 hr

Question 16

2 methods for DigiFAB (each for acute and chronic)

Answer 16

Acute:
1. unknown amount ingested- empiric 10-20 vials (20 if cardiac arrest, otherwise 10)
2. amount of digoxin ingested/0.5mg/vial

Chronic:
1. empiric-6 vials
2. (serum digoxin level ng/mL)x(wht in kg)/100 = dose in vials

Question 17

5 indications for Digifab

Answer 17

1. serum level >15ng/ml (acute)
2. tachy dysrhythmias
3. Brady dysrhythmias
4. cardiac arrest
5. Hyperkalemia >5meq/l
6. Visual impairment- every looks yellow
7. hypotension
8. acute ingestion >10 mg (0.3 mg/kg)
9. Steady state concentration >5ng/mL (chronic)
   5/10/15 rule
10. co-ingestion with other cardiotoxic drugs

Question 18

5 plants containing cardiac glycosides

Answer 18

1. fox gloves
2. yellow oleander
3. white oleander
4. lilly of valley
5. Dognbane
6. Rhododendron

Question 19

3 treatment for tachydysrythmias in digoxin toxicity

Answer 19

1. cardiovert or defibrilate
2. lidocaine (suppresses ventricular automaticity) ***avoid other anti arrythmics, will make problem worse
3. magnesium

Question 20

2 treatments for brady dysrythmias

Answer 20

1. Atropine (0.02 mg/kg/dose)
2. transcutaneous pacing

Question 21

3 other anti-depressants that can cause sodium channel blockade

Answer 21

1. citalopram
2. fluoxetine
3. venlafaxine