Labetalol
Systematic (IUPAC) name
2-hydroxy-5-[1-hydroxy-2- (4-phenylbutan-2-ylamino)-ethyl]-benzamide
Identifiers
CAS number	36894-69-6
ATC code	C07AG01
PubChem	3869
DrugBank	APRD01062
Chemical data
Formula	C19H24N2O3
Mol. mass	328.406 g/mol
Pharmacokinetic data
Bioavailability	90-100%
Protein binding	50%
Metabolism	hepatic pass metabolism,
Half life	Tablet: 6-8 hours; IV: 5.5 hours
Excretion	Excreted in urine, not removed by hemodialysis
Therapeutic considerations
Pregnancy cat.	C One of few drugs used for PIH
Legal status	℞ Prescription only
Routes	oral iv

Labetalol (Normodyne, Trandate, fixed combination with hydrochlorothiazide: Normozyde) is a drug that is a racemic mixture of four isomers. 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, is a mixed nonselective β blocker and selective β₂ agonist. It is used to treat high blood pressure. It works by blocking these adrenergic receptors, which decreases peripheral vascular resistance without significantly altering heart rate or cardiac output. The β:α antagonism of Labetalol is approximately 3:1.¹²

Indications

It has a particular indication in the treatment of pregnancy-induced hypertension which is commonly associated with pre-eclampsia. ³

It is also used to treat chronic hypertension of pheochromocytoma and hypertensive crisis.¹

Administration

Labetalol is available in 100, 200, and 300 mg tablets and intravenously (only as Trandate) in 5 mg/ml solution. Adults taking tablets usually start with 100 mg two times a day, with a maximum of 2.4 g/day. In an emergency situation, this may be higher. IV doses are usually started at 20mg over 2 minutes. Additional doses of 40mg, then 80mg may be administered every ten minutes as needed. Additional 80mg doses can be given to a total maximum dose of 300 mg. Additionally, labetalol can be administered by IV infusion at a rate of 2mg/minute, with a maximum dose of 300mg.

Side effects

Side effects may include:

• Drowsiness
• Fatigue
• Weakness
• Difficulty sleeping
• Diminished sexual function
• Scalp tingling which passes after time.
• A rare but potentially lethal side effect is respiratory distress.

Contraindications

Labetalol has relative contraindications for use in patients with asthma, congestive heart failure, any degree of heart block, bradycardia, or those in cardiogenic shock.

References

• Hodgson, Barbara B., and Kizior, Robert J. Saunders Nursing Drug Handbook 2006. St. Louis, MO: Elsevier, Saunders, 2006. bledsoe "prehospital emergency pharmacology" upper Saddle River, New Jersey: Pearson 2005

1. ^ ^{a b} Katzung, Bertram G. (2006). Basic and clinical pharmacology. New York: McGraw-Hill Medical, 170. ISBN 0-07-145153-6. 
2. ^ D A Richards, J Tuckman, and B N Prichard (October 1976). "Assessment of alpha- and beta-adrenoceptor blocking actions of labetalol.". Br J Clin Pharmacol 3 (5): 849–855. PMID PMC1428931. 
3. ^ http://www.bnf.org/bnf/bnf/56/2488.htm?q=%22labetalol%22