Digoxin
1. Background information
a. Definition
- Cardiac glycoside with narrow therapeutic index
- Used in:
- Atrial fibrillation (AF) – rate control
- Heart failure with reduced EF (HFrEF) – symptom relief
- Does not improve mortality in HF
b. Mechanism of action
Dual mechanism (high-yield):
- Na⁺/K⁺ ATPase inhibition → ↑ intracellular Ca²⁺ → ↑ contractility
- ↑ Vagal tone → ↓ AV node conduction → ↓ heart rate
c. Indications
- AF – rate control (especially sedentary or add-on)
- HFrEF – symptom improvement and ↓ hospitalisation
2. Assessment
a. Contra-indications
Absolute:
- Ventricular fibrillation
- High-degree AV block (without pacemaker)
- Digoxin toxicity
Avoid:
- Wolff–Parkinson–White + AF
Caution:
- Renal impairment (major risk factor for toxicity)
- Bradycardia
- Electrolyte imbalance (↓K⁺, ↓Mg²⁺, ↑Ca²⁺)
b. Drug interactions (AKT favourites)
Increase digoxin levels:
- Amiodarone
- Verapamil / diltiazem
- Macrolides
Increase toxicity risk:
- Loop/thiazide diuretics → hypokalaemia
c. Toxicity (CORE EXAM TOPIC)
Risk factors:
- Renal impairment (most common cause)
- Elderly
- Electrolyte disturbance
Clinical features:
| System | Features |
|---|---|
| GI | Nausea, vomiting, anorexia |
| Cardiac | Bradycardia, AV block, arrhythmias |
| Neuro | Confusion, weakness |
| Visual | Yellow/green vision (xanthopsia) |
Key AKT point:
- Hyperkalaemia = marker of severe toxicity
d. ECG features
Therapeutic (“digoxin effect”):
- Scooped ST depression (“reverse tick”)
- PR prolongation
👉 Normal effect, NOT toxicity
Toxicity:
- ↑ automaticity + ↓ AV conduction:
- Bradycardia
- AV block
- Atrial tachycardia with block
- Ventricular ectopics / VT
Classic:
- Bidirectional VT
e. Monitoring (WITH TIMELINES – VERY HIGH YIELD)
Baseline (before starting)
- U&Es (especially K⁺)
- Renal function
- Ca²⁺, Mg²⁺
- TFTs
After initiation / dose change
- Serum digoxin level:
- Take ≥6–12 hours after last dose
- Check at ~5–7 days (steady state)
Routine monitoring (stable patients)
- U&Es + renal function:
- Annually
- Increase frequency (every 3–6 months) if:
- Elderly
- Renal impairment
- Interacting drugs
- Electrolyte risk
Serum digoxin levels (NOT routine)
Check only if:
- Suspected toxicity
- Renal deterioration
- Drug interactions
- Dose change
- Poor adherence
Therapeutic range
- 0.7–2.0 ng/mL
Clinical monitoring
- Pulse (hold if bradycardic)
- Symptoms of toxicity
- ECG if indicated
3. Management (NICE CKS aligned)
a. Side effects AND what to do
| Side effect | Action |
|---|---|
| Mild GI upset | Review dose, monitor |
| Bradycardia | Withhold digoxin, check ECG |
| Confusion/visual symptoms | Check digoxin level + U&Es urgently |
| Suspected toxicity | STOP digoxin immediately |
👉 Important:
- Toxicity can occur within therapeutic range → treat clinically
b. Use in Primary Care
- Usually initiated by specialist
- GP role:
- Repeat prescribing
- Monitoring (U&Es, renal ± levels)
- Used for:
- AF (add-on rate control)
- Stable HF
- Avoid loading doses in primary care
c. Use in Secondary Care
Initiation:
- Loading (“digitalisation”) if rapid control needed
Indications:
- Acute AF (especially with HF)
- Decompensated HF
Management of toxicity
- Stop digoxin
- Check U&Es, digoxin level
- Correct electrolytes (especially K⁺)
- Treat arrhythmias
- Digoxin-specific antibody (Digoxin immune Fab) if:
- Life-threatening arrhythmia
- Severe hyperkalaemia
- Significant overdose
🔑 AKT ULTRA-HIGH YIELD SUMMARY
- MOA = ↑ contractility + ↓ AV conduction
- Indications = AF + HFrEF (symptom only)
- Check level ≥6–12h post-dose
- Steady state = ~5–7 days
- Annual U&Es (3–6 monthly if high risk)
- ↓K⁺ = biggest toxicity trigger
- Hyperkalaemia = severe toxicity
- Yellow vision = classic clue
- Scooped ST ≠ toxicity
- Antidote = Digoxin immune Fab
