Labetalol is a drug used to treat high blood pressure. It is effective as both an alpha and beta blocker. Labetalol is used effectively in the treatment of hypertensive emergencies, postoperative hypertension, phächromozotome-associated hypertension, and rebound hypertension. Common adverse effects include headache, dyspepsia, dizziness, nausea, lethargy, nasal congestion, and erectile dysfunction.
What is labetalol?
Labetalol is a blocking agent of adrenergic receptors. It competes with other catecholamines compatible with these sites. Labetalol has a relaxing effect on constricted vascular muscle. Labetalol hydrochloride is a white or cream-colored, crystalline, water-soluble powder. An injection of this agent is a clear, colorless to pale yellow, aqueous, isotonic solution for intravenous use. It has a pH range of 3.0 to 4.5. Per ml, the injection contains 5 mg of labetalol hydrochloride. Labetalol HCL is a racemate with the molecular formula C19H24N2O3*HCL and a molecular weight of 364.87. It has two asymmetric centers and exists as a molecular complex of two diastereomeric pairs of dilevalol.
Pharmacologic effects on body and organs
Labetalol is a dual-alpha and dual-beta receptor blocker. It blocks the activity of selective alpha and nonselective beta receptors in a single substance. Beta receptors are receptor molecules to which messengers such as epinephrine and norepinephrine dock. These messenger substances are part of the sympathetic nervous system. This is responsible for involuntary physical states of arousal. The excitation of betaadrenoceptors on blood vessels and the heart causes an acceleration of the heart rate and an increase in blood pressure. The effect on these receptors is potent and reversible. Labetalol is highly selective adrenergic for postsynaptic alpha1 receptors and nonselective for beta-adrenergic receptors. It is approximately equally potent for beta1- and beta2- receptors. The ratio of alpha to beta blockade depends on whether labetalol is received orally or intravenously. When received orally, the ratio of alpha- to beta-blockade is 1:3; intravenously, it is 1:7. Thus, labetalol can be understood as a beta-blocker with alpha-blocking activity. In comparison, labetalol is a weaker beta-blocker than, say, propranolol and has a weaker affinity for alpha receptors than phentolamine. Labetalol has intrinsic sympathomimetic activity. In particular, it is a partial agonist at beta2 receptors in vascular smooth muscle. Labetalol has a relaxing effect on vascular smooth muscle through a combination of this partial beta2 agonism with alpha1 blockade. This is vasodilatory and may cause a reduction in blood pressure. Similar to local anesthetics and sodium channel-blocking antiarrhythmics, labetalol also has membrane-stabilizing activity. By reducing sodium intake, labetalol reduces action potential firing, producing local anesthesia. The physiological effects of labetalol when administered intravenously cannot be predicted solely on the basis of its receptor-blocking effect. Blocking beta1 receptors should decrease heart rate. This is not true of labetalol. When labetalol is given in acute situations, it lowers peripheral vascular resistance as well as systemic blood pressure. The effect on heart rate, cardiac output, and stroke volume remains small despite alpha1, beta1, and beta2 blockade mechanisms. These effects were observed mainly in subjects in the upright position.
Medical use and use for treatment and prevention.
Labetalol finds application in the treatment of hypertension. It can be used alone or in combination with other drugs such as diuretics. The drug is usually administered after meals. Labetalol is effective in the treatment of hypertensive emergencies, postoperative hypertension, phächromozotome-associated hypertension, and rebound hypertension. The drug has a specific indication for the treatment of pregnancy-induced hypertension (preeclampsia). It is also used as an alternative in the treatment of severe hypertension when it is necessary to bring blood pressure under control as quickly as possible. Labetalol is used to regulate blood pressure under anesthesia when needed.In a clinical study in pharmacologically severe hypertension, blood pressure in supine patients decreased by an average of 11/7 mmHG after injection of 0.25 mg/kg. Further injections of 0.5 mg/kg up to a cumulative dose of 1.75 mg/kg achieved further dose-dependent reductions in blood pressure. Administered as a continuous intravenous infusion, at a mean dose of 136 mg over a period of two to three hours, labetalol lowers blood pressure by an average of 60/35 mmHg. After cessation of treatment, blood pressure gradually increases.
Risks and side effects
The most common potential side effects include increased liver function values, congestive heart failure, lethargy, erectile dysfunction, urinary discomfort, nausea, low blood pressure, visual disturbances, nasal congestion, and hypersensitivity reactions. In some cases, orthostasis syndrome occurs. In this, patients experience a rapid decrease in blood pressure when they change from a lying or sitting position to an upright standing position. Drowsiness and even fainting may occur. Patients should be monitored for this side effect. Labetalol should be avoided in asthma or chronic obstructive pulmonary disease, very low blood pressure, severe heart disease, severe heart failure, and slowed heart rate. Labetalol may pass into breast milk in small amounts. Breastfeeding mothers should inform their doctor about this. Ingestion of labetol may worsen thinking performance and reactions. Additional consumption of alcohol may further lower blood pressure and increase certain side effects of the drug. Prior to surgery under anesthesia, as well as eye surgery, the medication of Labetol drugs should be noted. Symptoms of overdose include decrease in heart rate, dizziness, and fainting.
