Labetalol Hydrochloride (Page 3 of 4)

Drug & OR Laboratory Test Interactions

The presence of labetalol metabolites in the urine may result in falsely elevated levels of urinary catecholamines, metanephrine, normetanephrine, and vanillylmandelic acid when measured by fluorimetric or photometric methods. In screening patients suspected of having a pheochromocytoma and being treated with labetalol HCl, a specific method, such as a high performance liquid chromatographic assay with solid phase extraction (e.g., J Chromatogr 385:241,1987) should be employed in determining levels of catecholamines.
Labetalol HCl has also been reported to produce a false-positive test for amphetamine when screening urine for the presence of drugs using the commercially available assay methods Toxi-Lab ® A (thin-layer chromatographic assay) and Emit-d.a.u.® (radioenzymatic assay). When patients being treated with labetalol have a positive urine test for amphetamine using these techniques, confirmation should be made by using more specific methods, such as a gas chromatographic-mass spectrometer technique.

Carcinogenesis & Mutagenesis & Impairment Of Fertility

Long-term oral dosing studies with labetalol HCl for 18 months in mice and for 2 years in rats showed no evidence of carcinogenesis. Studies with labetalol HCl using dominant lethal assays in rats and mice and exposing microorganisms according to modified Ames tests showed no evidence of mutagenesis.

Pregnancy


Teratogenic Effects: Pregnancy Category C: Teratogenic studies were performed with labetalol in rats and rabbits at oral doses up to approximately six and four times the maximum recommended human dose (MRHD), respectively. No reproducible evidence of fetal malformations was observed. Increased fetal resorptions were seen in both species at doses approximating the MRHD. A teratology study performed with labetalol in rabbits at intravenous doses up to 1.7 times the MRHD revealed no evidence of drug-related harm to the fetus. There are no adequate and well-controlled studies in pregnant women. Labetalol should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Nonteratogenic Effects: Hypotension, bradycardia, hypoglycemia, and respiratory depression have been reported in infants of mothers who were treated with labetalol HCl for hypertension during pregnancy. Oral administration of labetalol to rats during late gestation through weaning at doses of two to four times the MRHD caused a decrease in neonatal survival.

Labor & Delivery

Labetalol HCl given to pregnant women with hypertension did not appear to affect the usual course of labor and delivery.

Nursing Mothers


Small amounts of labetalol (approximately 0.004% of the maternal dose) are excreted in human milk. Caution should be exercised when Labetalol hydrochloride injection is administered to a nursing woman.

Pediatric Use


Safety and effectiveness in pediatric patients have not been established.

ADVERSE REACTIONS

Labetalol hydrochloride injection is usually well tolerated. Most adverse effects have been mild and transient and, in controlled trials involving 92 patients, did not require labetalol HCl withdrawal. Symptomatic postural hypotension (incidence, 58%) is likely to occur if patients are tilted or allowed to assume the upright position within 3 hours of receiving Labetalol hydrochloride injection. Moderate hypotension occurred in 1 of 100 patients while supine. Increased sweating was noted in 4 of 100 patients, and flushing occurred in 1 of 100 patients.

The following also were reported with Labetalol hydrochloride injection with the incidence per 100 patients as noted:

Cardiovascular System: Ventricular arrhythmia in 1.

Central and Peripheral Nervous Systems: Dizziness in 9, tingling of the scalp/skin in 7, hypoesthesia (numbness) and vertigo in 1 each.

Gastrointestinal System: Nausea in 13, vomiting in 4, dyspepsia and taste distortion in 1 each.

Metabolic Disorders: Transient increases in blood urea nitrogen and serum creatinine levels occurred in 8 of 100 patients; these were associated with drops in blood pressure, generally in patients with prior renal insufficiency.

Psychiatric Disorders: Somnolence/yawning in 3.

Respiratory System: Wheezing in 1.
Skin: Pruritus in 1.The incidence of adverse reactions depends upon the dose of labetalol HCl. The largest experience is with oral labetalol HCl (see labetalol hydrochloride Tablets Product Information for details). Certain of the side effects increased with increasing oral dose, as shown in the following table that depicts the entire US therapeutic trials data base for adverse reactions that are clearly or possibly dose related.

Labetalol HCI Daily Dose (mg) 200 300 400 600 800 900 1200 1600 2400
Number of patients 522 181 606 608 503 117 411 242 175
Dizziness (%) 2 3 3 3 5 1 9 13 16
Fatigue 2 1 4 4 5 3 7 6 10
Nausea <1 0 1 2 4 0 7 11 19
Vomiting 0 0 <1 <1 <1 0 1 2 3
Dyspepsia 1 0 2 1 1 0 2 2 4
Paresthesia 2 0 2 2 1 1 2 5 5
Nasal stuffiness 1 1 2 2 2 2 4 5 6
Ejaculation failure 0 2 1 2 3 0 4 3 5
Impotence 1 1 1 1 2 4 3 4 3
Edema 1 0 1 1 1 0 1 2 2

In addition, a number of other less common adverse events have been reported:
Cardiovascular: Hypotension, and rarely, syncope, bradycardia, heart block.
Liver and Biliary System: Hepatic necrosis, hepatitis, cholestatic jaundice, elevated liver function tests.
Hypersensitivity: Rare reports of hypersensitivity (e.g., rash, urticaria, pruritus, angioedema, dyspnea) and anaphylactoid reactions.
The oculomucocutaneous syndrome associated with the beta-blocker practolol has not been reported with labetalol HCl during investigational use and extensive foreign marketing experience.Clinical Laboratory Tests: Among patients dosed with labetalol hydrochloride Tablets, there have been reversible increases of serum transaminases in 4% of patients tested and, more rarely, reversible increases in blood urea.

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