Mechanism of Action

Competitively block beta-adrenergic receptors, preventing catecholamines (epinephrine, norepinephrine) from driving the sympathetic fight-or-flight response. Beta-1 receptors live mainly in the heart: blockade lowers heart rate, contractility, and AV-node conduction, reducing myocardial oxygen demand. Beta-2 receptors live in the lungs and vasculature: nonselective blockade removes bronchodilation and vasodilation, so nonselective agents risk bronchospasm. Every approved indication traces back to one idea — reduce cardiac workload.

SNS β₁-blockade cascade

Block β₁ receptorscompetitive blockade of cardiac sympathetic receptors
↓ heart rate, ↓ contractility, ↓ AV conductionnegative chronotrope + inotrope + dromotrope
↓ renin releaseβ₁ blockade in the kidney lowers renin → less angiotensin II
↓ blood pressure & ↓ myocardial O₂ demandthe shared endpoint behind every indication

Common Medications

metoprololPrototype

cardioselective β₁; succinate form for HFrEF

atenolol

cardioselective β₁

propranolol

nonselective β₁/β₂

carvedilol

nonselective plus alpha-1 blockade; favored in HFrEF

Indications

hypertension

heart failure with reduced EF

improves long-term survival; carvedilol/metoprolol succinate

post-myocardial infarction

lowers myocardial O₂ demand, limits remodeling, reduces mortality

stable angina

atrial fibrillation rate control

slows AV-node conduction

Side Effects

bradycardia

expected pharmacologic effect; becomes a hold issue below 60 bpm

orthostatic hypotension

reduced cardiac output; rise slowly

fatigue

common adherence barrier

cold extremities

sexual dysfunction

common, embarrassing adherence barrier — ask directly

depressed mood

reported adherence barrier

Contraindications & Interactions

Contraindications

asthma

nonselective agents; β₂ blockade → bronchospasm

severe COPD

nonselective agents

decompensated heart failure

negative inotropy worsens acute failure; start only when compensated

high-grade AV block

2nd/3rd-degree block without pacemaker

Interactions

non-dihydropyridine calcium channel blockers

verapamil/diltiazem — additive bradycardia and AV block

insulin and sulfonylureas

masks hypoglycemia warning signs

Administration & Monitoring

count apical pulse for 60 seconds

before every dose

measure blood pressure before dose

hold dose and notify providerHoldHR < 60 bpm

hold dose and notify providerHoldSBP < 90 mmHg

antidote: glucagon for overdose

reverses β-blocker overdose bradycardia/hypotension refractory to atropine — bypasses the β-receptor to raise cAMP

taper over 1–2 weeks to discontinue

never stop abruptly

monitor blood glucose in diabetics

tachycardia warning is masked

weigh daily if prescribed for heart failure

Patient Teaching

check your pulse before each dose

do not stop the drug abruptly

rebound tachycardia and hypertensive crisis

rise slowly from sitting or lying

orthostatic hypotension

watch for sweating as a low-sugar clue

racing heart won't warn you

report new wheezing or shortness of breath

report fatigue or sexual side effects

alternatives exist — don't quit silently

weigh yourself daily for heart failure

Report Nowescalate immediately

abrupt-withdrawal rebound Hallmark

stopping suddenly → rebound tachycardia + hypertensive crisis from receptor upregulation; never discontinue abruptly — taper over 1–2 weeks

symptomatic bradycardiaHR < 60 bpm

hold and notify; overdose can progress to high-grade heart block

severe hypotensionSBP < 90 mmHg

bronchospasm

nonselective agents (propranolol, carvedilol) in asthma/COPD

masked hypoglycemia

blunts tachycardia warning in diabetics; sweating remains the reliable autonomic clue

Clinical Pearl

"-olol" = slow and low — lower heart rate, lower blood pressure, lower myocardial O₂ demand, and every indication connects to that triad. Never stop abruptly, and if a diabetic on a beta-blocker is sweating for no reason, check the glucose — the racing heart won't warn you.