OB/ Pharm | Labetalol

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Labetalol is an oral and parenteral medication primarily utilized for the management of hypertension. It functions as a combined selective, competitive alpha1-blocker and nonselective, competitive beta-blocker. Labetalol effectively targets beta1-receptors in the heart, beta2-receptors in bronchial and vascular smooth muscle, and alpha1-receptors in vascular smooth muscle. The drug's pharmacodynamic action is driven primarily by its beta-blocking capabilities, but the ratio of alpha- to beta-receptor activity shifts based on the route of administration: it is 1:3 when administered orally and 1:7 when administered intravenously. The alpha1-blocking component is critical because it inhibits peripheral vasoconstriction, lowering systemic vascular resistance without compromising total peripheral blood flow, which minimizes the reductions in cardiac output commonly seen with standard beta-blockers.

Administration & Dosing Oral Administration: Labetalol is completely absorbed from the gastrointestinal tract, but due to extensive first-pass metabolism, its absolute bioavailability is only 25% (though taking it with food increases this absorption). Peak plasma concentrations occur within 1 to 2 hours, and peak effects happen within 2 to 4 hours. The full antihypertensive effect is visible within 1 to 3 hours, allowing clinicians to safely ensure there is no exaggerated hypotensive response during an office visit. Intravenous (IV) Administration: Patients must be kept in a supine position during IV administration, and blood pressure must be closely monitored before, during, and after administration. Direct IV injections require no dilution and should be pushed slowly over 2 minutes. For continuous infusion, the initial rate is 2 mg/minute, which is subsequently adjusted based on the patient's blood pressure response. The maximum effect of an IV dose is seen rapidly, within just 5 minutes. Providers should stop the IV infusion once a satisfactory blood pressure response is achieved and transition to oral labetalol as soon as the patient's supine blood pressure begins to rise.

Adverse Reactions & Safety Profile One of the most notable and common adverse effects is orthostatic hypotension, which has an incidence rate of up to 58% and is especially prevalent following intravenous use. Severe adverse reactions include hepatotoxicity, hepatic necrosis, myocardial infarction, AV block, heart failure, cardiac arrest, bronchospasm, and severe allergic responses like angioedema. Mild to moderate adverse reactions frequently encompass nausea (up to 19%), dizziness (up to 16%), fatigue, nasal congestion, elevated hepatic enzymes, and ejaculation or erectile dysfunction.

Pregnancy and Lactation Labetalol is frequently used to manage hypertension during pregnancy, a condition that inherently increases maternal and fetal risks such as preeclampsia and intrauterine growth restriction. While labetalol crosses the placenta, extensive medical experience has not identified a drug-associated risk for major birth defects. However, healthcare providers must carefully monitor neonates born to treated mothers for signs of hypotension, bradycardia, hypoglycemia, and respiratory depression. For lactating mothers, labetalol is generally considered compatible with breast-feeding, as only minuscule amounts (approximately 0.004% of the maternal dose) are excreted in human milk. Despite this, alternative beta-blockers like propranolol may be preferred for mothers nursing premature infants