Carvedilol

Mechanism

Mechanism of Action

Third-generation non-selective adrenergic antagonist that combines potent blockade of β₁ and β₂ receptors with selective blockade of postsynaptic α₁ receptors. Additionally, it has direct intrinsic antioxidant properties and antiproliferative effects on vascular smooth muscle. α₁inhibition decreases SVR through vasodilation of resistance arterioles, avoiding the initial increase in afterload characteristic of traditional beta-blockers. β₁ blockade prevents reflex tachycardia induced by vasodilation and protects the myocardium from toxicity due to excess catecholamines.

Pharmacokinetics

Key Pharmacokinetics

• Routes: Oral (tablets, extended-release capsules). Its absorption slows down if it is administered together with food, reducing the incidence of orthostatic hypotension.
• Bioavailability: Low, approximately 25-30% per dominant stereospecific hepatic first pass.
• Lipophilia: High, with a wide volume of distribution and binding to plasma proteins greater than 98%.
• Metabolism: Hepatic through the microsomal cytochrome system CYP2D6 and CYP2C9.
• Half-life: 7 to 10 hours.
• Excretion: Mainly fecal through bile (>80%); elimination through urine is less than 2%.

Indicators and dose

Approved and Off-label Indications

Approved: Stable chronic congestive heart failure with reduced ejection fraction (associated with ACEI/ARBs and diuretics); clinically stable post-acute myocardial infarction left ventricular dysfunction; essential essential arterial hypertension.

Off-label: Severe portal hypertension and primary prevention of bleeding from esophageal varices.

Dosage and Adjustments

Heart Failure (Oral): Start with 3,125 mg every 12 hours orally for a minimum period of 2 weeks. If adequately tolerated, increase progressively to 6.25 mg, then to 12.5 mg and until reaching a maximum target dose of 25 mg every 12 hours (in patients < 85 kg) or 50 mg every 12 hours (in patients > 85 kg).

Renal adjustment: Does not require preliminary modifications to the ordinary dosage.

Hepatic adjustment: Contraindicated in severe hepatic failure or Child-Pugh B/C due to the imminent risk of massive systemic accumulation of the active ingredient.

Security

Contraindications

Absolute: Acute decompensated heart failure requiring intravenous inotropes, active bronchial asthma, second or third degree AV block without pacemaker, severe sinus bradycardia, clinically proven severe hepatic failure.

Relative: Unstable diabetes mellitus, peripheral vascular disease with intermittent claudication.

Adverse Effects (ADR)

Common: Dizziness, pronounced orthostatic vertigo (secondary to peripheral α₁ blockade), postural arterial hypotension, chronic fatigue, mild weight gain, transient hyperglycemia in diabetics.

Serious: Severe exacerbation of acute heart failure at the start of treatment, high-grade atrioventricular block, severe bronchospasm.

Interactions

Insulin and oral antidiabetics: Enhances the hypoglycemic effect and can mask the associated sympathetic alarm symptoms.

CYP2D6 inhibitors (e.g., amiodarone, fluoxetine): Increase serum levels of carvedilol, significantly increasing the risk of sinus block and severe hypotension.

Pregnancy and Breastfeeding

FDA Classification: Category C. Risk of utero-placental hypoperfusion and neonatal bradycardia. Its administration is not recommended unless there is an imperative maternal clinical need. It is excreted in breast milk.