Digoxin toxicity
Background
- Positive inotropic effect
- Inhibits Na-K pump -> incr extracelluar K, incr intracellular Na -> incr intracellular Ca
- Increases vagal tone
- Can lead to bradyarrhythmias (esp in young)
- Increases automaticity
- Can lead to tachyarrhythmias (esp in elderly)
- Renally cleared
- Hemodialysis does not work
- 1 fab vial binds 0.5mg of digoxin
Risk Factors
- Electrolyte Imbalance
- Hypokalemia, hypomagnesemia, Hypercalcemia
- Hypovolemia
- Renal insufficiency
- Cardiac ischemia
- Hypothyroidism
- Meds
- CCBs, amiodarone
Clinical Manifestations
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
- Nausea/vomiting
- Abdominal pain
Neuro
- Confusion
- Weakness
- Visual disturbances
- Yellow halos
- Scotomas
- Delirium
Work-Up
- Dig level
- Normal = 0.8-2 ng/mL (ideal = 0.7-1.1)
- May have toxicity even with "therapeutic" levels
- Measure serum level at least 6 hours after acute ingestion (if stable), immediately for chronic ingestion
- If measure before this may be falsely elevated due to incomplete drug distribution
- Normal = 0.8-2 ng/mL (ideal = 0.7-1.1)
- Chemistry
- Hyperkalemia level correlates with degree of toxicity
- Hypokalemia increases susceptibility in chronic toxicity
- Hypomagnesemia is common
- Cr/BUN
- Urine output
- ECG (serial)
Treatment
Fab Fragment Therapy
- 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
- Side effects
- Allergic reaction
- Withdrawal of dig effect:
- CHF, a fib w/ RVR
- Hypokalemia
- Initial response time ~ 20min, peak effect ~ 90min
- How To Use
- 1. Neither amount ingested nor digoxin level are known:
- Adult dose
- 10 vials over 30 min
- Peds dose
- 5 vials over 30 min
- Repeat dose if clinical response is inadequate
- Adult dose
- 2. Amount ingested is known but digoxin level is unknown
- Step 1: Calculate total body load (TBL)
- TBL = dose (in mg) ingested
- Step 2: Calculate number of vials needed
- Number of vials = TBL X 2 (round up to nearest whole number)
- 3. Steady state digoxin level is known
- Number of vials = (dig level(in ng/mL) X pt wt) / 100
- 4. Chronic toxicity without severe signs
- Give half the recommended dose
- Otherwise may unmask the condition for which the pt is taking digoxin
- 5. Cardiac Arrest
- 20 vials administered undiluted by IV bolus
- 1. Neither amount ingested nor digoxin level are known:
Activated charcoal
- Questionable efficacy
- Only an adjunctive tx; NOT an alternative to fab fragment therapy
- Consider only if present within 1 hr of ingestion
- 1g/kg (max 50g)
Rhythm Disturbances
- Fab fragments is the agent of choice for all dysrhythmias!
- Bradyarrhythmias (symptomatic)
- Atropine 0.5mg IV
- Pacing
- Tachyarrhythmias
- Lidocaine
- 1-3mg/kg over several minutes, followed by 1-4mg/min
- Phenytoin
- May enhance AV conduction
- Infuse at 25-50 mg/min to a loading dose of 10-15mg/kg
- Lidocaine
- Cardioversion
- Consider lower energy settings (25-50J)
Hyperkalemia
- Treat with Fab, not with usual meds
- Once fab is given hyperkalemia will rapidly correct
- Aggressive tx with potassium-lowering agents could cause sig hypokalemia following therapy
- If Fab is not available and hyperkalemia is life-threatening then treat
- Calcium is controversial (some say dangerous, others say not)
Hypokalemia
- Chronic intoxication
- Raise level to 3.5-4
- Acute intoxication
- Do not treat (likely that potassium level is rapidly rising)
Hypomagnesemia
- Treat with 1-2g over 10-20 min
- Monitor for resp depresion
- Avoid in pts with:
- Renal failure
- Bradydysrhythmias/conduction blocks
Source
Rosen's