Difficulty: Intermediate | Prerequisites: Autonomic nervous system, electrolyte balance, diuretics study notes
Digoxin strengthens the heart and slows its rate, but it has a narrow therapeutic window that makes toxicity a constant concern, especially when potassium is low. Adrenergic agonists (epinephrine, norepinephrine, dopamine) are used in acute, life-threatening situations to raise blood pressure and support cardiac output. Men's health drugs cover BPH (alpha-1 blockers and 5-alpha reductase inhibitors), erectile dysfunction (PDE-5 inhibitors, which must never be combined with nitrates), and testosterone replacement.
Cardiac glycoside
A class of drugs derived from the foxglove plant that increase the force of myocardial contraction and slow heart rate. Digoxin is the only one still in clinical use. Think of it as a drug that makes the heart beat stronger but slower.
Positive inotropic effect
An increase in the force of cardiac contraction. In simple terms, the heart squeezes harder with each beat.
Negative chronotropic effect
A decrease in heart rate. In simple terms, the heart beats fewer times per minute.
Digoxin toxicity
A dangerous condition that occurs when digoxin blood levels rise above the therapeutic range, or when hypokalemia makes the heart overly sensitive to digoxin. Early signs include GI symptoms and visual changes; late signs include dysrhythmias.
Adrenergic agonist
A drug that stimulates the sympathetic nervous system by activating adrenergic receptors (alpha and beta). Think of these as "adrenaline-like" drugs used in emergencies to raise blood pressure and heart rate.
Extravasation
Leakage of an IV drug (especially a vasopressor) into surrounding tissue, causing tissue necrosis. In simple terms, if the IV slips out of the vein, these drugs can destroy the tissue around it.
Benign prostatic hyperplasia (BPH)
Non-cancerous enlargement of the prostate gland that compresses the urethra, causing difficulty urinating. Very common in men over 50.
PDE-5 inhibitor
A drug that blocks phosphodiesterase type 5, increasing blood flow to the penis and producing an erection. Think of it as the class that includes sildenafil (Viagra).
5-Alpha reductase inhibitor
A drug that blocks the conversion of testosterone to dihydrotestosterone (DHT), shrinking the prostate over time. In simple terms, it reduces the hormone that makes the prostate grow.
Tags: digoxin, Lanoxin, cardiac glycoside, positive inotrope, negative chronotrope, digoxin toxicity, Digibind, DigiFab, therapeutic range, hypokalemia
Inhibits the sodium-potassium ATPase pump in cardiac cells
This increases intracellular calcium, which strengthens myocardial contraction (positive inotropic effect)
Also slows conduction through the AV node, reducing heart rate (negative chronotropic effect)
Activates the vagus nerve (parasympathetic), further slowing the heart
Heart failure (improves cardiac output by strengthening contractions)
Atrial fibrillation and atrial flutter (controls ventricular rate by slowing AV conduction)
0.5 to 2.0 ng/mL
This is a narrow therapeutic index, meaning the difference between a therapeutic dose and a toxic dose is small
Levels above 2.0 ng/mL are considered toxic
Take an apical pulse for a full 60 seconds
Hold the dose and notify the provider if the heart rate is below 60 bpm in an adult (below 70 in a child, below 90 to 110 in an infant)
Check the most recent serum digoxin level and potassium level
Early signs:
GI symptoms: anorexia (often the first sign), nausea, vomiting, diarrhoea
Visual disturbances: blurred vision, yellow-green halos around lights (xanthopsia), photophobia
Fatigue, weakness
Late signs:
Cardiac dysrhythmias (the most dangerous): bradycardia, heart block, ventricular tachycardia, ventricular fibrillation
Any new dysrhythmia in a patient on digoxin should be treated as possible toxicity until proven otherwise
Hypokalemia is the primary electrolyte concern. When potassium is low, digoxin binds more readily to the sodium-potassium ATPase pump, intensifying its effects and triggering toxicity even at "normal" digoxin levels. This is why potassium must be monitored closely in any patient on digoxin, especially those also taking loop or thiazide diuretics.
Other imbalances that increase toxicity risk: hypomagnesemia, hypercalcemia.
Digoxin immune Fab (Digibind, DigiFab)
These are antibody fragments that bind to digoxin in the blood, inactivating it
Used for life-threatening toxicity (severe dysrhythmias, serum level above 10 ng/mL, ingestion of a large amount)
Always take an apical pulse for 60 seconds before administration
Monitor serum digoxin levels (draw at least 6 to 8 hours after the last dose for an accurate trough)
Monitor potassium, magnesium, and calcium levels
Teach patients to report anorexia, nausea, visual changes, or palpitations
Assess renal function (digoxin is excreted by the kidneys; impaired renal function increases toxicity risk)
Avoid giving with antacids (reduce absorption); separate by 2 hours
Be aware of drug interactions: amiodarone, verapamil, and quinidine can increase digoxin levels
Tags: epinephrine, Adrenalin, norepinephrine, Levophed, dopamine, Intropin, dobutamine, Dobutrex, vasopressor, extravasation, phenylephrine, sympathomimetic
Epinephrine (Adrenalin): stimulates alpha-1, beta-1, and beta-2 receptors
Norepinephrine (Levophed): primarily alpha-1 and beta-1
Dopamine (Intropin): dose-dependent effects on dopaminergic, beta-1, and alpha-1 receptors
Dobutamine (Dobutrex): primarily beta-1 (inotropic support)
Phenylephrine: primarily alpha-1 (pure vasoconstrictor)
Stimulate adrenergic receptors, mimicking the sympathetic nervous system
Alpha-1 stimulation: vasoconstriction, raising blood pressure
Beta-1 stimulation: increased heart rate and contractility
Beta-2 stimulation: bronchodilation, vasodilation in skeletal muscle
Cardiac arrest (epinephrine)
Anaphylaxis (epinephrine)
Severe hypotension and shock (norepinephrine, dopamine)
Heart failure with low cardiac output (dobutamine)
Nasal congestion (phenylephrine, which is the decongestant that can raise blood pressure in patients on antihypertensives)
Hypertension
Tachycardia, dysrhythmias
Angina
Headache, anxiety, tremor
Hyperglycemia
Tissue necrosis if extravasation occurs
Extravasation is the leakage of a vasopressor (such as norepinephrine or dopamine) out of the vein and into surrounding tissue. Because these drugs cause intense vasoconstriction, extravasation can lead to local tissue ischaemia and necrosis.
Prevention: administer through a central line whenever possible; if using a peripheral IV, choose a large vein and monitor the site frequently
Treatment: inject phentolamine (Regitine) into the affected area as soon as extravasation is detected. Phentolamine is an alpha blocker that reverses the vasoconstriction.
Monitor the IV site every 1 to 2 hours for signs of infiltration: blanching, swelling, coolness, pain
Tags: tamsulosin, Flomax, doxazosin, Cardura, prazosin, terazosin, alpha-1 blocker, finasteride, Proscar, dutasteride, Avodart, 5-alpha reductase inhibitor, BPH
Mechanism of Action
Block alpha-1 receptors in the smooth muscle of the prostate and bladder neck, causing relaxation. This improves urine flow and relieves obstructive symptoms. These drugs also lower blood pressure by causing vasodilation (alpha-1 receptors are also on blood vessels).
Drug Names
Tamsulosin (Flomax) – most commonly prescribed for BPH; more selective for the prostate, so less hypotension
Doxazosin (Cardura)
Prazosin (Minipress)
Terazosin (Hytrin)
How Alpha-1 Blockers Lower BP
By blocking alpha-1 receptors on blood vessels, these drugs cause vasodilation and reduce peripheral vascular resistance. This is why orthostatic hypotension is a major concern.
Nursing Implications
Administer at bedtime to minimise orthostatic hypotension and dizziness
First-dose hypotension: warn patients about dizziness and fainting after the first dose
Teach patients to rise slowly from sitting or lying positions
Monitor blood pressure
Tamsulosin should be taken 30 minutes after the same meal each day
Report dizziness, lightheadedness, or fainting
Mechanism of Action
Block the enzyme 5-alpha reductase, which converts testosterone to dihydrotestosterone (DHT). DHT drives prostate growth, so reducing it shrinks the prostate over time. Effects take 3 to 6 months to become noticeable.
Drug Names
Finasteride (Proscar) – also sold as Propecia at a lower dose for hair loss
Dutasteride (Avodart)
Side Effects
Decreased libido
Erectile dysfunction
Decreased ejaculate volume
Gynecomastia (rare)
Lowers PSA levels by approximately 50%, which can mask prostate cancer detection
Contraindications
Contraindicated in pregnancy and in women who may become pregnant
Pregnant women should not even handle crushed or broken tablets because the drug can be absorbed through the skin and cause birth defects in a male foetus (abnormal genital development)
Men taking these drugs should use a condom during intercourse if their partner is or may become pregnant
Tags: sildenafil, Viagra, tadalafil, Cialis, vardenafil, Levitra, avanafil, Stendra, PDE-5 inhibitor, nitrate contraindication
Drug Names
Sildenafil (Viagra)
Tadalafil (Cialis) – longest duration of action (up to 36 hours)
Vardenafil (Levitra)
Avanafil (Stendra)
All end in "-afil."
Mechanism of Action
Inhibit phosphodiesterase type 5 (PDE-5), an enzyme that breaks down cyclic GMP. By preserving cyclic GMP, smooth muscle in the penile vasculature relaxes, increasing blood flow and producing an erection in the presence of sexual stimulation. These drugs do not cause an erection on their own; sexual arousal is required.
Side Effects
Headache
Flushing
Nasal congestion
Dyspepsia
Visual disturbances (blurred vision, blue-tinted vision, especially with sildenafil)
Dizziness
Priapism (prolonged, painful erection lasting more than 4 hours; a medical emergency)
Contraindication: Nitrates
PDE-5 inhibitors are absolutely contraindicated with nitrates (nitroglycerin, isosorbide mononitrate, isosorbide dinitrate) and nitrate-containing recreational drugs (amyl nitrite, "poppers"). Both PDE-5 inhibitors and nitrates cause vasodilation. Combining them produces severe, potentially fatal hypotension.
Patients must not take a PDE-5 inhibitor within 24 hours of a short-acting nitrate (48 hours for tadalafil, given its longer half-life). If a patient on a PDE-5 inhibitor presents with chest pain, nitrates must not be given.
Tags: testosterone, AndroGel, testosterone cypionate, Depo-Testosterone, anabolic steroid, pregnancy category X
Testosterone is classified as Category X (contraindicated in pregnancy). It causes virilisation of a female foetus and other developmental abnormalities. Women who are or may become pregnant must avoid contact with testosterone products (gels, patches, injections).
Liver toxicity (hepatotoxicity), especially with oral formulations
Polycythaemia (increased red blood cell count), which raises the risk of blood clots, stroke, and pulmonary embolism
Acne, oily skin
Mood changes, aggression, irritability
Gynaecomastia (paradoxically, because some testosterone converts to oestrogen)
Testicular atrophy and reduced sperm production (exogenous testosterone suppresses the body's own production)
Fluid retention, oedema
Sleep apnoea (can worsen existing sleep apnoea)
Increased risk of cardiovascular events (under ongoing study)
Prostate enlargement; contraindicated in known or suspected prostate cancer
Students often think a normal digoxin level means the patient cannot have toxicity. Hypokalemia can cause toxicity even when the digoxin level is within the therapeutic range (0.5 to 2.0 ng/mL).
Many students confuse the early signs of digoxin toxicity (GI and visual) with the late signs (cardiac dysrhythmias). The GI and visual symptoms come first; the dysrhythmias are the dangerous late stage.
Students sometimes assume PDE-5 inhibitors cause erections automatically. They do not; sexual stimulation is still required for the drug to work.
A common error is thinking alpha-1 blockers for BPH only affect the prostate. They also cause systemic vasodilation and can lower blood pressure significantly, especially with the first dose.
⚠️ Digoxin therapeutic range (0.5 to 2.0 ng/mL) and the link between hypokalemia and toxicity are among the most tested concepts in nursing pharmacology.
⚠️ Always take an apical pulse for 60 seconds before giving digoxin. Hold if HR is below 60.
⚠️ The antidote for digoxin toxicity is Digibind (digoxin immune Fab).
⚠️ PDE-5 inhibitors + nitrates = absolute contraindication. This appears on almost every exam.
⚠️ Extravasation of vasopressors is treated with phentolamine.
⚠️ Pregnant women must not handle crushed finasteride or dutasteride tablets.
⚠️ Tamsulosin at bedtime to reduce first-dose hypotension.
Fill in the blank: The therapeutic range for digoxin is ______ to ______ ng/mL.
0.5 to 2.0 ng/mL.
True or False: PDE-5 inhibitors can be safely combined with nitroglycerin.
False. This combination can cause fatal hypotension.
Fill in the blank: The antidote for digoxin toxicity is ______.
Digoxin immune Fab (Digibind or DigiFab).
True or False: Finasteride shrinks the prostate within the first week of use.
False. Effects take 3 to 6 months to become noticeable.
True or False: A nurse should take a radial pulse before giving digoxin.
False. An apical pulse should be taken for a full 60 seconds.
Q: A patient on digoxin reports seeing yellow-green halos around lights and has lost their appetite. What should the nurse suspect?
A: Early digoxin toxicity. Anorexia and visual disturbances (yellow-green halos, blurred vision) are classic early signs. The nurse should hold the next dose, check the serum digoxin level and potassium, and notify the provider.
Q: A patient on digoxin has a potassium level of 3.2 mEq/L and a digoxin level of 1.8 ng/mL. Is the patient at risk for digoxin toxicity?
A: Yes. Although the digoxin level is within the therapeutic range, the low potassium (hypokalemia) makes the heart more sensitive to digoxin. The patient is at significant risk for toxicity and needs potassium replacement.
Q: A nurse notices blanching and swelling at the IV site of a patient receiving norepinephrine. What is the priority action?
A: Stop the infusion immediately; this is extravasation. Notify the provider and prepare to administer phentolamine into the affected area to reverse the vasoconstriction and prevent tissue necrosis.
Q: A patient taking sildenafil presents to the emergency department with chest pain. The patient asks for nitroglycerin. What should the nurse do?
A: Do not administer nitroglycerin. Combining a PDE-5 inhibitor with a nitrate can cause severe, life-threatening hypotension. The nurse should notify the provider and use alternative pain management.
Q: A patient newly prescribed tamsulosin for BPH asks when to take it. What is the best advice?
A: Take tamsulosin 30 minutes after the same meal each day, preferably at bedtime. Taking it at bedtime reduces the risk of orthostatic hypotension and dizziness, which are most likely after the first dose.
Q: A patient's wife is pregnant. He has been prescribed finasteride for BPH. What important teaching should the nurse provide?
A: His wife must not handle crushed or broken finasteride tablets, as the drug can be absorbed through the skin and cause birth defects in a male foetus. He should also use a condom during intercourse while she is pregnant.
Digoxin connects directly to the diuretics material: loop and thiazide diuretics cause hypokalemia, which is the primary driver of digoxin toxicity. Adrenergic agonists tie back to the autonomic nervous system and connect forward to shock management and critical care. Alpha-1 blockers for BPH overlap with the antihypertensive drugs since they also lower blood pressure. PDE-5 inhibitors connect to the nitrates used for angina, which will appear in cardiovascular drugs Part II.
Digoxin, Lanoxin, cardiac glycoside, positive inotrope, negative chronotrope, digoxin toxicity, Digibind, DigiFab, digoxin immune Fab, therapeutic range, hypokalemia, epinephrine, norepinephrine, Levophed, dopamine, dobutamine, vasopressor, extravasation, phentolamine, sympathomimetic, adrenergic agonist, BPH, benign prostatic hyperplasia, tamsulosin, Flomax, doxazosin, prazosin, terazosin, alpha-1 blocker, finasteride, Proscar, dutasteride, Avodart, 5-alpha reductase inhibitor, DHT, sildenafil, Viagra, tadalafil, Cialis, vardenafil, PDE-5 inhibitor, nitrate contraindication, erectile dysfunction, testosterone, AndroGel, pregnancy category X, nursing pharmacology, cardiovascular drugs, men's health pharmacology