Digoxin toxicity

Background

Positive inotropic effect
- Inhibits Na-K pump -> increased intracellular Na -> increased intracellular Ca
Increases vagal tone
Decreases refractory time; increases automaticity
- Increases risk of dysrhythmias
Renally cleared
Hemodialysis does not work

AV block

Dig level
- Normal = 0.8-2 ng/mL
  - May have toxicity even with "therapeutic" levels
- Measure serum level at least 6 hours after acute ingestion, immediately for chronic ingestion
  - If measure before this may be falsely elevated due to incomplete drug distribution
Chemistry
- Hyperkalemia level correlates with degree of toxicity
  - Hyperkalemia does not cause death; lowering K+ does not reduce mortality
- Hypokalemia increases susceptibility in chronic toxicity
- Hypomagnesemia is common
Cr/BUN
Urine output
ECG (serial)

Cardiac

Any type of dysrhythmia is possible except for rapidly conducted atrial arrhythmias
Most common:
- PVCs
- Bradycardia
Digitalis Effect
- T wave changes
- QT interval shortening
- Scooped ST segments with depression in lateral leads

GI

Neuro

Activated charcoal 1g/kg (max 50g)
- Only an adjunctive tx; NOT an alternative to fab fragment therapy
- Consider only if present within 2 hr of ingestion

Hyperkalemia
- Do not treat! Do not give calcium!
  - Once fab is given hyperkalemia will rapidly correct
    - Aggressive tx with potassium-lowering agents could cause sig hypokalemia following therapy

Indications for Rx of rhythm disturbances

    -hemodynamic compromise caused by bradycardia or tachycardia

    -frequent/complex ventricular ectopy

Bradycardia

    -Atropine

    -Electrical pacing

    -K contraindicated UNLESS severe hypok*

         -if tachycardic, give K*

         -if bradycardic, can worsen with K*

Tachyarrhythmias, increased automaticity

-K

    -Mag

    -Lidocaine

    -Phenytoin

    -Cardioversion

Digoxin immune Fab

    -Ab bind to dig, remove drug from serum and myocardium

    -Ab-dig complex excreted in the urine

Indications

Severe rhythm disturbances refractory to conventional therapy
End-organ dysfunction
Hyperkalemia >5 after acute overdose
Pacemaker (may mask cardiac dysrhythmia)
Consider for:
- Dig level > 10 in acute ingestion
- Dig level > 4 in chronic ingestion
- If adult acutely ingests > 10mg
- If child acutely ingests > 4mg

    -co-ingestion of cardiotoxic drugs: CCBs, beta-blockers, or TCAs

Empiric Dosages

-Chronic toxicity and unkown level: 4-6 vials (1/2 vial in child)

-Cariac arrest = 20 vials undiluted by IV bolus

Calculated Dosages: see package insert

-1 vial (40mg) binds 0.6mg dig

-Dose (vials) = body load (mg)/0.6 (mg/vial)

     -dig body load estimated from ingested dose or serum level

    -(dig level x wt in kg)/ 100 = # of vials

Kinetics

-Onset: 20mins

-Full effect: 90mins

- Note** digitalis level unreliable after digibind administration, must follow patient clinically

-potential allergic reactions

-w/d of dig effect:

    -CHF

    -hypoK

    -dig levels not usable

Rosen's, UpToDate