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Nursing Field Notes / Cardiovascular Pharmacology · Cardiotonic (Cardiac Glycoside)

Digoxin 💛

Lanoxin — the classic narrow therapeutic index drug

NG-208 Cardiac Drugs ADHD-friendly visual edition

Digoxin makes the heart squeeze harder and beat slower — great for heart failure and atrial fibrillation, terrible if the dose creeps even a little too high. Narrow therapeutic index means the safe dose and the toxic dose are close together — this is the drug that punishes skipped assessments.

📄 Simple Nursing original — opens in Drive →

💪 Squeeze harder, beat slower+inotropic (↑contractility), −chronotropic (↓HR), −dromotropic (↓AV conduction).
🧪 Therapeutic range0.8–2 ng/mL — above that is toxic.
✋ Apical pulse × 1 full minuteHold & notify provider if <60 bpm.
🟡 Halos / yellow-green vision= classic toxicity sign. Antidote: DigiFab.
⚡

WHAT IT DOES

STEP 1 · SQUEEZE + SLOW

Two effects, three big words — memorize the words and the drug makes sense.

💓 Mechanism: positive inotrope, negative chronotrope & dromotrope

Digoxin increases cardiac output through positive inotropic activity — an increase in the force of contraction. It also slows conduction velocity through the AV node (negative dromotropic effect) and decreases heart rate (negative chronotropic effect).

AV 💪 +Inotropic force of contraction ↑ 🐢 −Chronotropic heart rate ↓ 🚦 −Dromotropic AV conduction ↓ = more output per beat, fewer beats per minute
🧠 “INO up, CHRONO & DROMO down.” Ino = force (up). Chrono = rate (down). Dromo = conduction speed through the AV node (down). One drug, opposite directions on purpose.

🎯 Why we give it — “Reason”

  • 📉 Heart failure — stronger contraction improves cardiac output
  • 💓 Atrial fibrillation — slows AV conduction to control ventricular rate

🚫 Contraindications

  • Digitalis toxicity, known hypersensitivity
  • Ventricular fibrillation / ventricular tachycardia
  • Cardiac tamponade, restrictive cardiomyopathy
  • AV block
👀

WATCH FOR

STEP 2 · TOXICITY — NARROW MARGIN

The therapeutic dose and the toxic dose sit close together — this is why every dose gets checked.

🧪 Therapeutic range — 0.8–2 ng/mL

Levels drawn immediately before the next dose (trough), or 6–8 hours after the last dose regardless of route. Above roughly 2 ng/mL is considered toxic and is reported to the provider.

👁️ Toxicity signs — visual first

🟡 halos / yellow-green vision
  • 👁️ Visual disturbances — blurring, yellow-green halos ("Van Gogh vision")
  • 🍽️ GI: nausea, anorexia
  • 💓 Arrhythmias
  • 🧠 Confusion — especially in older adults
  • 😴 Weakness, drowsiness, headache
🧠 “Yellow halo = too much Lanoxin.” If a patient describes lights with a yellow-green ring, think digoxin toxicity first.

🧂 Hypokalemia raises toxicity risk

Na+/K+-ATPase pump site Low K+ = less competition → digoxin binds MORE

Potassium and digoxin compete for the same binding site on the pump. When K+ is low, there's less competition — more digoxin binds, increasing the chance of toxicity even at a "normal" dose.

🧠 Thiazide & loop diuretics cause hypokalemia — giving them alongside digoxin is a classic setup for toxicity. Watch potassium closely.

🔁 Interactions

  • Thyroid hormone — decreases digoxin's effect
  • Thiazide/loop diuretics — increase hypokalemia risk → increased digoxin toxicity risk

💉 Antidote: Digoxin immune Fab (DigiFab)

For serious toxicity, digoxin immune Fab binds free digoxin so it can no longer act on the heart — used for life-threatening arrhythmias or a significantly elevated level.

🧑‍🏫

TEACH

STEP 3 · THE RULE THAT PREVENTS THE ER VISIT

One physical assessment, done correctly, catches most problems before they become toxicity.

✋ Apical pulse for a FULL minute before every dose

⏱️ FULL 60 SECONDS 🩺 Apical site ❌ <60 bpm → HOLD dose, notify provider

Count the apical pulse (not radial) for a full 60 seconds before administering. If the rate is <60 bpm in an adult, hold the dose and notify the provider — don't give it and hope.

🧠 “Apical, full minute, under 60 — don't give it.” Radial pulses can miss irregular or weak beats; the apex catches the true rate the drug is acting on.

📋 What to teach the patient

  • ✋ Check your own pulse before each dose; report a rate under 60 or a big change
  • ⚖️ Weigh daily — sudden gain can signal worsening HF
  • 👁️ Report visual changes, nausea, confusion right away
  • 💊 Never double up a missed dose

👶 Pediatric note

In children, the dose is withheld and the provider notified if the apical pulse is below 70 bpm; in infants, below 90 bpm. Kids run faster baseline heart rates, so the hold threshold is higher than the adult 60 bpm rule.

⚡

QUICK RECALL

SAY IT OUT LOUD
💪 +Inotrope, −chrono/dromotropestronger squeeze, slower/less-conducted beat
🧪 0.8–2 ng/mLtherapeutic range — above is toxic
✋ Apical × 1 min, hold if <60notify the provider, don't give
🟡 Yellow-green halosclassic toxicity sign · antidote = DigiFab
🎯 Cover & check — 4 rapid-fire questions
Q1: Name digoxin's three cardiac effects in one sentence.
Positive inotrope (↑force of contraction), negative chronotrope (↓heart rate), negative dromotrope (↓AV node conduction).
Q2: A patient's digoxin level comes back at 2.6 ng/mL. What does that mean?
That's above the therapeutic range of 0.8–2 ng/mL — it's a toxic level and should be reported to the provider.
Q3: Why does hypokalemia increase the risk of digoxin toxicity?
Potassium and digoxin compete for the same binding site on the Na+/K+-ATPase pump. With less potassium around to compete, more digoxin binds — increasing its effect and toxicity risk even at an unchanged dose.
Q4: Before giving digoxin, the apical pulse is 52 bpm. What do you do?
Hold the dose and notify the provider — it's below the 60 bpm threshold. Always count the apical pulse for a full minute before administering.