Prescribers should be cautious in the use of labetalol for nursing mothers.Pediatric: no studies have established safety or usefulness in this population.Geriatric: the elderly are more likely to experience dizziness when taking labetalol. Labetalol should be dosed with caution in the elderly and counseled on this side effect. Side effects
Common
Neurologic: headache (2%), dizziness (11%)
Gastrointestinal: nausea (6%), dyspepsia (3%)
Cholinergic: nasal congestion (3%), ejaculation failure (2%)
Respiratory: dyspnea (2%)
Other: fatigue (5%), vertigo (2%), orthostatic hypotensionLow blood pressure with standing is more severe and more common with IV formulation (58% vs 1%) and is often the reason larger doses of the oral formulation cannot be used. Rare
Fever
Muscle cramps
Dry eyes
Heart block
Hyperkalemia
Hepatotoxicity
Drug eruption similar to lichen planus
Hypersensitivity - which may result in a lethal respiratory distress

Contraindications
Labetalol is contraindicated in people with overt cardiac failure, greater-than-first-degree heart block, severe bradycardia, cardiogenic shock, severe hypotension, anyone with a history of obstructive airway disease including asthma, and those with hypersensitivity to the drug. Chemistry
The minimum requirement for adrenergic agents is a primary or secondary amine separated from a substituted benzene ring by one or two carbons. This configuration results in strong agonist activity. As the size of the substituent attached to the amine becomes greater, particularly with respect to a t-butyl group, then the molecule typically is found to have receptor affinity without intrinsic activity, and is, therefore, an antagonist. Labetalol, with its 1-methyl-3-phenylpropyl substituted amine, is greater in size relative to a t-butyl group and therefore acts predominantly as an antagonist. The overall structure of labetalol is very polar.
This was created by substituting the isopropyl group in the standard beta-blocker structure with an aralkyl group, including a carboxamide group on the meta position, and by adding a hydroxyl group on the para position.Labetalol has two chiral carbons and consequently exists as four stereoisomers. Two of these isomers, the (S,S)- and (R,S)- forms are inactive. The third, the (S,R)-isomer, is a powerful α1 blocker. The fourth isomer, the (R,R)-isomer which is also known as dilevalol, is a mixed nonselective β blocker and selective α1 blocker. Labetalol is typically given as a racemic mixture to achieve both alpha and beta receptor blocking activity. Labetalol acts by blocking alpha and beta adrenergic receptors, resulting in decreased peripheral vascular resistance without significant alteration of heart rate or cardiac output. The β:α antagonism of labetalol is approximately 3:1.It is chemically designated in International Union of Pure and Applied Chemistry (IUPAC) nomenclature as 2-hydroxy-5-[1-hydroxy-2-[(1-methyl-3-phenylpropyl)amino]ethyl]benzamide monohydrochloride. Pharmacology
Mechanism of action
Labetalols dual alpha and beta adrenergic antagonism has different physiological effects in short- and long-term situations. In short-term, acute situations, labetalol decreases blood pressure by decreasing systemic vascular resistance with little effect on stroke volume, heart rate and cardiac output. During long-term use, labetalol can reduce heart rate during exercise while maintaining cardiac output by an increase in stroke volume.Labetalol is a dual alpha (α1) and beta (β1/β2) adrenergic receptor blocker and competes with other Catecholamines for binding to these sites. Its action on these receptors are potent and reversible. Labetalol is highly selective for postsynaptic alpha1- adrenergic, and non-selective for beta-adrenergic receptors.