Digoxin toxicity

Background

Positive inotropic effect

inhibits Na-K pump; ultimately increases intracellular Ca which leads to increased contractility

AV block

RISK FACTORS

Increased sensitivity to dig

    -electrolyte disturbances (eg hypoK)

    -hypoxia

    -cardiac ischemia

    -Increased Dig levels

    -renal insufficiency

    -CCBs

Toxic Side Effects

GI

    -N/V

Neurologic

    -Classic: yellow hallows around vision

Cardiac

Vagal

    Rhythm disturbances

    -depressed condxn/impulse formation

    -enhanced automaticity

    -can see almost any rhythm except afib with RVR; hence there is no diagnostic arrhythmia

    -serum dig levels often not helpful*

HyperK

    -asscociated with worse outcomes in acute OD

-Gastric empytying if SOON after ingestion

Charcoal (need 10x the ingested dose); usually 25-100g PO

Toxic effects may be delayed SEVERAL hours (serum/myocardial levels equilibrate in 6-8h)

Temporary discontinuation of dig often sufficient

Tx of hyperkalemia

    -bicarb, glucose/insulin may be ineffective

    -calcium contraindicated (usually)

    -dig-Ab

    -Forced diuresis, hemodialysis, hemoperfusion ineffective in removing dig

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

Digibind

    -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

    -hyperkalemia >5 after ACUTE OD

    -very large ingested dose or very high serum dig level (eg4-10)

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

Empiric Dosages

-Acute Ingestion: give 10-20 vials over 30 minutes through 0.22 micron filter

-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

Adapted from Rosens 7th Edition