What is the difference between metoprolol, carvedilol and labetalol❔❔❔

β-blockers are an important class of cardiovascular drugs. It plays an irreplaceable role in the prevention and treatment of chronic heart failure, ischemic heart disease, hypertension and arrhythmia. Metoprolol, carvedilol and labetalol are three types of beta-blockers commonly used in clinic. What is the difference between them?

1. Mechanism:

Metoprolol is a selective β1-blocker. 

Carvedilol and labetalol are nonselective beta-blockers. The ratios of their α and β receptor blocking effects were about 1:10 and 1:3, respectively. Carvedilol has antioxidant properties. Labetalol has a strong blocking effect on α-receptors. Labetalol has intrinsic sympathomimetic activity and is less lipid soluble. Therefore, labetalol is theoretically less central nervous system adverse effects.

2. Clinical application:

Increased sympathetic excitability will accelerate the occurrence and development of heart failure. 

Metoprolol and carvedilol: Metoprolol succinate, carvedilol and bisoprolol have been shown in clinical trials to reduce the risk of death, sudden death, and hospitalization in patients with chronic heart failure. They can improve patients' cardiac function and quality of life. Labetalol cannot be used in the treatment of chronic heart failure because of its intrinsic sympathomimetic activity.

labetalol: It blocks α1-receptors. It directly dilates blood vessels and lowers blood pressure without affecting placental and renal blood flow. It can also promote fetal lung maturation. It is the preferred antihypertensive drug for pregnancy-induced hypertension.

3. Dosage.

Chronic heart failure:

• Metoprolol succinate sustained-release tablets: The initial dose is 11.875-23.750 mg once a day. The target dose is 190 mg, once a day. Food does not affect its absorption.
• Carvedilol: The initial dose is 3.125 mg, twice a day. The target dose is 25-50 mg, once a day. It must be taken with food to slow absorption and reduce the occurrence of orthostatic hypotension.

The dose at which the resting heart rate is reduced to 60 beats/min is the target dose or the maximum tolerated dose of β-blockers.

Pregnancy-induced hypertension:

• Labetalol tablets: 100-200 mg each time, 2-3 times a day. Dosage needs to be adjusted according to blood pressure. The maximum dose is 2400 mg daily. Take after meals.

4. Adverse effects.

Effects on Peripheral Resistance: Carvedilol and labetalol have α1-blocker effects compared to metoprolol. It dilates peripheral blood vessels and reduces vascular resistance. In theory, it may be more suitable for patients with hypertension and peripheral arterial disease. Labetalol can cause intermittent reductions in nipple blood flow. It may cause nipple numbness, paleness and pain (Raynaud's phenomenon).

Effects on Respiratory Function: Metoprolol is a selective β1-blocker. It has relatively little effect on β2-receptors. Patients with coronary heart disease and chronic obstructive pulmonary disease can choose metoprolol (or bisoprolol).

Effects on Glucose Metabolism: Catecholamines increase glycogenolysis by agonizing β2-receptors. Therefore, metoprolol has less effect on blood sugar and is less likely to cause hypoglycemia. However, β-blockers can mask symptoms of hypoglycemia, such as tachycardia and tremor. In addition, studies have found that carvedilol has vasodilator and antioxidant effects. It improves insulin resistance and lowers triglycerides.

Orthostatic hypotension: Carvedilol and labetalol have α1-blocker effects. It relaxes vascular smooth muscle, especially in the upright position. A small number of patients may develop orthostatic hypotension 2 to 4 hours after taking the drug.

5. Discontinue medication.

Long-term use of β-blockers can increase the expression of β-receptors. Since a large number of β-receptors are available for catecholamines, it will promote cardiac and vasoconstriction. If β-blockers are suddenly discontinued, a rebound in blood pressure can develop. Patients with ischemic heart disease can induce angina attacks and even myocardial infarction. The entire withdrawal period should be at least 2 weeks. During this period, patients with known ischemic heart disease should be closely monitored.