Digoxin Epidemiology



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Digoxin

Epidemiology

Untreated chronic toxicity  15-30% mortality within 1/52

Toxic dose

>10x normal daily dose (>75mcg/kg in child); any ingestion with suicidal intention usually potentially life threatening

Potentially lethal: >10mg adult, >4mg child  give digibind
Level <1: therapeutic 1-2: supra 2-3: potentially toxic >3.2: probably toxic

>15: potentially lethal, needs digibind

In paeds

Are more resistant to effects of digoxin

Pharmacology

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, indomethacin

Peak Level

Reached at 6hrs

Symptoms

Chronic OD usually asymptomatic (yellow vision, decr VA, chromatopsia, xanthopsia)

N+V (within 2-4hrs), AP, ECG changes as below, lethargy, confusion, psych, weakness



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 / Mg

Digoxin effect: Scooped ST segment depression – mostly in inferior and anterior leads; reverse tick

flat / inverted / biphasic T waves

short QT

PR prolongation

Prominent U waves

J point depression



Toxicity: 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; not seen in chronic toxicity (more likely to see hypoK))

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), salbutamol, frusemide

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 (flecainide)



De-contamination

Charcoal: if <1hr

MDAC: if significant toxicity

Elimination

No

Antidote

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)

Indications: imminent threat to life or potential for:

Refractory life threatening arrhythmia / cardiac arrest

Refractory hyperK >5

Dig >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  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 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 (4%), allergy rare, may get AF, exac of CCF (3%)


Disposition

Monitor 6-12hrs (from presentation / digibind administration); then can discharge if no GI Sx, normal K, normal dig levels, normal ECG

Chronic usually requires admission





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