Digoxin
Epidemiology
Toxic dose
Untreated chronic toxicity  15-30% mortality within 1/52
>10x normal daily dose (>75mcg/kg in child)
Potentially lethal: >10mg
Level <1: therapeutic
adult, >4mg child  give digibind
1-2: supra 2-3: potentially toxic
>15: potentially lethal, needs digibind
In paeds
Pharmacology
>3.2: probably toxic
Are more resistant to effects of digoxin
Na-K ATPase inhibitor  incr intracellular Ca and Na, decr intracellular K; weak +ive inotrope;
AVN blockade, slows conduction, incr vagal tone, decr AP duration, incr myocardial automaticity;
very large VOD; marked decr clearance in renal failure; narrow therapeutic index
Interactions which incr dig level: amiodarone, flecainide, verapamil,
quinidine, spironolactone, erythromycin / roxi / tetracycline
Peak Level
Symptoms
Reached at 6hrs
Chronic OD usually asymptomatic (yellow vision, decr VA, chromatopsia, xanthopsia); N+V
(within 2-4hrs), AP, ECG changes as below, lethargy, confusion, psych
Death from cardiac collapse at 8-12hrs
Potentially life threatening: K >5.5, decr BP, arrhythmia, cardiac arrest
Investigations
ECG: Worsened by hypoK / Mg, hyperCa
PR prolongation
Scooped ST segment depression – mostly in inferior and anterior leads; reverse tick = use,
not toxicity
Diminished T wave amplitude
Short QT interval
U waves
Due to incr automaticity AF with slow V response <60, AVB, junctional escape rhythm, sinus
brady, SAN arrest, atrial tachy with variable AVB, VT/VF/TdP, V ectopics (most common)
Bloods: hyperK (marker of severity, occurs early, may be more accurate than dig level; if >5.5 =
100% mortality without digibind)
dig level (levels taken >6hrs after ingestion correlate with toxicity; do at 4hrs then Q2hrly
until definitive trt or levels improving; unreliable once digibind given as levels will incr)
incr Ur and Cr; Mg (worse toxicity if low)
Treatment
Refractory to conventional resus in cardiac arrest – continue 30mins after digibind given
Mng hyperK: insulin (10iu + 50ml 50% dex), NaHCO3 (1-2mmol/kg); aim K <5; try not to use Ca
(but role is unclear)
Mng arrhythmia: atropine for AVB, may need pacing; MgSO4 may help in V arrhythmia
If V arrhythmia: lignocaine 1mg/kg IV over 2mins (or phenytoin)
Do not use: as will induce V arrhythmia: cardioversion (use low setting if necessary)
isoprenaline
As will induce V arrhythmia and worsen AVB: Ia (procainamide, quinine), Ic
Decontamination Charcoal: if <1hr
MDAC: if significant toxicity
Elimination
Antidote
No
Digibind: ab’s which bind to digoxin  excreted in urine (may need plasma exchange if renal
failure); onset 30mins, max at 4hrs; half life is 12hrs (longer than dig); 1 ampoule binds 0.5mg dig
Indications: imminent threat to life or potential for:
Refractory life threatening arrhythmia / cardiac arrest
Refractory hyperK >5
Dig >20 at 6hrs or >15 at any time
>10mg (4mg in child) ingested
In chronic: mod-severe GI Sx, any Sx if decr renal fx, arrhythmia unlikely to be tolerated for
Long …. With an incr dig level  decr mortality, hospital LOS, cost of care
Dose: ACUTE: ingested dose (mg) x 0.8 x 2 = no. of ampoules to give (if don’t know dose, use 5
ampoules if stable, 10 ampoules if unstable, and repeat 5 after 30mins if no
Disposition
response; give 20 ampoules in cardiac arrest)
CHRONIC: (dig level (mmol/L) x weight (kg)) / 100 = no. of ampoules to give (usually
need 2 ampoules  if no response at 30mins, give further 2)
Dilute dose in 100ml N saline and give over 30mins
40mg/ampoule = decr dig level by 1 = binds 500mcg dig
SE: occurs in <5%; rebound hypoK, allergy rare, may get AF, exac of CCF due to loss of inotropic
action
Monitor 6hrs (from presentation / digibind administration); then can discharge if no GI Sx,
normal K, normal dig levels, normal ECG
Chronic usually requires admission