Source:http://www4.wiwiss.fu-berlin.de/dailymed/resource/drugs/3606
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Labetalol Hydrochloride (Injection, Solution)
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Labetalol hydrochloride injection is intended for
intravenous use in hospitalized patients. DOSAGE MUST BE INDIVIDUALIZED
depending upon the severity of hypertension and the response of the
patient during dosing. Patients should always be kept in a supine position during the period
of intravenous drug administration. A substantial fall in blood pressure
on standing should be expected in these patients. The patient's
ability to tolerate an upright position should be established before
permitting any ambulation, such as using toilet facilities. Either of two methods of administration of
labetalol hydrochloride injection may be used: a) repeated intravenous
injections, b) slow continuous infusion. Repeated Intravenous Injection: Initially,
labetalol hydrochloride injection should be given in a dose of 20
mg labetalol HCl (which corresponds to 0.25 mg/kg for an 80 kg patient)
by slow intravenous injection over a 2-minute period. Immediately before the injection and at 5 and 10 minutes after injection,
supine blood pressure should be measured to evaluate response. Additional
injections of 40 mg or 80 mg can be given at 10 minute intervals until
a desired supine blood pressure is achieved or a total of 300 mg labetalol
HCl has been injected. The maximum effect usually occurs within 5
minutes of each injection. Slow Continuous Infusion: Labetalol
hydrochloride injection is prepared for intravenous continuous infusion
by diluting the drug with commonly used intravenous fluids (see below).
Examples of methods of preparing the infusion solution are: Labetalol hydrochloride injection 200 mg is added to 160
mL of a commonly used intravenous fluid such that the resultant 200
mL of solution contains 200 mg of labetalol hydrochloride, 1 mg/mL.
The diluted solution should be administered at a rate of 2 mL/min
to deliver 2 mg/min. Alternatively, 200 mg of
labetalol hydrochloride injection is added to 250 mL of a commonly
used intravenous fluid. The resultant solution will contain 200 mgof labetalol hydrochloride, approximately 2 mg/3 mL. The diluted solution
should be administered at a rate of 3 mL/min to deliver approximately
2 mg/min. The rate of infusion of the diluted
solution may be adjusted according to the blood pressure response,
at the discretion of the physician. To facilitate a desired rate of
infusion, the diluted solution can be infused using a controlled administration
mechanism, e.g., graduated burette or mechanically driven infusion
pump. Since the half-life of labetalol is 5
to 8 hours, steady-state blood levels (in the face of a constant rate
of infusion) would not be reached during the usual infusion time period.
The infusion should be continued until a satisfactory response is
obtained and should then be stopped and oral labetalol hydrochloride
started. The effective intravenous dose is usually in the range of
50 to 200 mg. A total dose of up to 300 mg may be required in some
patients. Blood
Pressure Monitoring: The blood pressure should be monitored
during and after completion of the infusion or intravenous injections.
Rapid or excessive falls in either systolic or diastolic blood pressure
during intravenous treatment should be avoided. In patients with excessive
systolic hypertension, the decrease in systolic pressure should be
used as indicator of effectiveness in addition to the response of
the diastolic pressure. Initiation of Dosing with Labetalol Hydrochloride
Tablets: Subsequent oral dosing with labetalol hydrochloride
tablets should begin when it has been established that the supine
diastolic blood pressure has begun to rise. The recommended initial
dose is 200 mg, followed in 6 to 12 hours by an additional dose
of 200 or 400 mg, depending on the blood pressure response. Thereafter, inpatient titration with labetalol hydrochloride
tablets may proceed as follows: * If needed, the total daily dose may be given
in three divided doses. While in the hospital,
the dosage of labetalol hydrochloride tablets may be increased at
1 day intervals to achieve the desired blood pressure reduction. For subsequent outpatient titration or maintenance dosing
see Labetalol Hydrochloride Tablets Product Information DOSAGE AND ADMINISTRATION for additional
recommendations. Compatibility with commonly used intravenous fluids: Parenteral drug products should be inspected visually
for particulate matter and discoloration prior to administration,
whenever solution and container permit. Labetalol
hydrochloride injection was tested for compatibility with commonly
used intravenous fluids at final concentrations of 1.25 mg to 3.75
mg labetalol hydrochloride per mL of the mixture. Labetalol hydrochloride
injection was found to be compatible with and stable (for 24 hours
refrigerated or at room temperature) in mixtures with the following
solutions: Ringers Injection, USP Lactated Ringers Injection, USP 5% Dextrose and Ringers Injection 5% Lactated
Ringers and 5% Dextrose Injection 5% Dextrose
Injection, USP 0.9% Sodium Chloride Injection,
USP 5% Dextrose and 0.2% Sodium Chloride Injection,
USP 2.5% Dextrose and 0.45% Sodium Chloride
Injection, USP 5% Dextrose and 0.9% Sodium Chloride
Injection, USP 5% Dextrose and 0.33% Sodium
Chloride Injection, USP Labetalol hydrochloride
injection was NOT compatible with 5% Sodium Bicarbonate Injection,
USP.
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Labetalol hydrochloride is an adrenergic receptor
blocking agent that has both selective alpha- and nonselective
beta-adrenergic receptor blocking actions in a single substance. Labetalol HCl is a racemate, chemically designated as
5-[1-hydroxy-2-[(1-methyl-3-phenylpropyl) amino] ethyl]-salicylamide
monohydrochloride, and has the following structural formula: Labetalol hydrochloride
has the molecular formula CHNO���HCl and a molecular weight of 364.87. It has
two asymmetric centers and therefore exists as a molecular complex
of two diastereoisomeric pairs. Dilevalol, the R,R' stereoisomer,
makes up 25% of racemic labetalol. Labetalol
hydrochloride is a white or off-white crystalline powder, soluble
in water. Labetalol hydrochloride injection
is a clear, colorless to light yellow aqueous sterile isotonic solution
for intravenous injection. It has a pH range of 3.0 to 4.5. Each mL
contains 5 mg labetalol hydrochloride, USP, 45 mg anhydrous dextrose,
0.1 mg edetate disodium; 0.8 mg methylparaben and 0.1 mg propylparaben
as preservatives; citric acid monohydrate and sodium hydroxide, as
necessary, to bring the solution into the pH range.
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Labetalol combines both selective, competitive alpha-adrenergic blocking and nonselective, competitive beta-adrenergic
blocking activity in a single substance. In man, the ratios of alpha-
to beta-blockade have been estimated to be approximately 1:3 and 1:7
following oral and intravenous administration, respectively. Beta-agonist activity has been demonstrated in animals with minimal
beta-agonist (ISA) activity detected. In animals, at doses
greater than those required for alpha- or beta-adrenergic blockade,
a membrane-stabilizing effect has been demonstrated. Pharmacodynamics The capacity
of labetalol to block alpha-receptors in man has been demonstrated
by attenuation of the presser effect of phenylephrine and by a significant
reduction of the presser response caused by immersing the hand in
ice-cold water (���cold-presser test���). Labetalol's
beta-receptor blockade in man was demonstrated by a small
decrease in the resting heart rate, attenuation of tachycardia produced
by isoproterenol or exercise, and by attenuation of the reflex tachycardia
to the hypotension produced by amyl nitrite. Beta-receptor
blockade was demonstrated by inhibition of the isoproterenol-induced
fall in diastolic blood pressure. Both the alpha- and beta-blocking
actions of orally administered labetalol contribute to a decrease
in blood pressure in hypertensive patients. Labetalol consistently,
in dose-related fashion, blunted increases in exercise-induced blood
pressure and heart rate, and in theirdouble product. The pulmonary
circulation during exercise was not affected by labetalol dosing. Single oral doses of labetalol administered in patients
with coronary artery disease had no significant effect on sinus rate,
intraventricular conduction, or QRS duration. The AV conduction time
was modestly prolonged in 2 of 7 patients. In another study, intravenous
labetalol slightly prolonged AV nodal conduction time and atrial effective
refractory period with only small changes in heartrate. The effects
on AV nodal refractoriness were inconsistent. Labetalol produces dose-related falls in blood pressure without reflex
tachycardia and without significant reduction in heart rate, presumably
through a mixture of its alpha-blocking and beta-blocking effects.
Hemodynamic effects are variable with small nonsignificant changes
in cardiac output seen in some studies but not others, and small decreases
in total peripheral resistance. Elevated plasma renins are reduced. Doses of labetalol that controlled hypertension did not
affect renal function in mild to severe hypertensive patients with
normal renal function. Due to the alpha-receptor blocking activity of labetalol, blood pressure is
lowered more in the standing than in the supine position, and symptoms
of postural hypotension can occur. During dosing with intravenous
labetalol, the contribution of the postural component should be considered
when positioning patients for treatment, and patients should not be
allowed to move to an erect position unmonitored until their ability
to do so is established. In a clinical pharmacologic
study in severe hypertensives, an initial 0.25 mg/kg injection of
labetalol, administered to patients in the supine position, decreased
blood pressure by an average of 11/7 mmHg. Additional injections of
0.5 mg/kg at 15 minute intervals up to a total cumulative dose of
1.75 mg/kg of labetalol caused further dose-related decreases in blood
pressure. Some patients required cumulative doses of up to 3.25 mg/kg.
The maximal effect of each dose level occurred within 5 minutes. Following
discontinuation of intravenous treatment with labetalol, the blood
pressure rose gradually and progressively approaching pretreatment
baseline values within an average of 16 to 18 hours in the majority
of patients. Similar results were obtained in
the treatment of patients with severe hypertension requiring urgent
blood pressure reduction with an initial dose of 20 mg (which corresponds
to 0.25 mg/kg for an 80 kg patient) followed by additional doses of
either 40 or 80 mg at 10 minute intervals to achieve the desired effect
or up to a cumulative dose of 300 mg. Labetalol
administered as a continuous intravenous infusion, with a mean dose
of 136 mg (27 to 300 mg) over a period of 2 to 3 hours (mean
of 2 hours and 39 minutes) lowered the blood pressure by an average
of 60/35 mmHg. Exacerbation of angina and, in
some cases, myocardial infarction and ventricular dysrhythmias have
been reported after abrupt discontinuation of therapy with beta-adrenergic
blocking agents in patients with coronary artery disease. Abrupt withdrawal
of these agents in patients without coronary artery disease has resulted
in transient symptoms, including tremulousness, sweating, palpitation,
headache and malaise. Several mechanisms have been proposed to explain
these phenomena, among them increased sensitivity to catecholamines
because of increased numbers of beta-receptors. Although beta-adrenergic receptor blockade is useful in the treatment
of angina and hypertension, there are also situations in which sympathetic
stimulation is vital. For example, in patients with severely damaged
hearts, adequate ventricular function may depend on sympathetic drive.
Beta-adrenergic blockade may worsen AV block by preventing the necessary
facilitating effects of sympathetic activity on conduction. Beta-adrenergic blockade results in passive bronchial constriction
by interfering with endogenous adrenergic bronchodilator activity
in patients subject to bronchospasm and may also interfere with exogenous
bronchodilators in such patients. Pharmacokinetics and Metabolism Following
intravenous infusion, the elimination half-life is about 5.5 hours
and the total body clearance is approximately 33 mL/min/kg. The plasma
half-life of labetalol following oral administration is about 6 to
8 hours. In patients with decreased hepatic or renal function, the
elimination half-life of labetalol is not altered; however, the relative
bioavailability in hepatically impaired patients is increased due
to decreased���first-pass���metabolism. The metabolism of labetalol is mainly through conjugation to glucuronide
metabolites. These metabolites are present in plasma and are excreted
in the urine and, via the bile, into the feces. Approximately 55%
to 60% of a dose appears in the urine as conjugates or unchanged labetalol
within the first 24 hours of dosing. Labetalol
has been shown to cross the placental barrier in humans. Only negligible
amounts of the drug crossed the blood-brain barrier in animal studies.
Labetalol is approximately 50% protein bound. Neither hemodialysis
nor peritoneal dialysis removes a significant amount of labetalol
from the general circulation (<1%).
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Labetalol HCl injection is contraindicated in bronchial
asthma, overt cardiac failure, greater than first degree heart block,
cardiogenic shock, severe bradycardia, other conditions associated
with severe and prolonged hypotension, and in patients with a history
of hypersensitivity to any component of the product (see WARNINGS). Beta-blockers,
even those with apparent cardioselectivity, should not be used in
patients with a history of obstructive airway disease, including asthma.
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Labetalol hydrochloride injection, 5 mg/mL, is supplied
in: 4 mL (20 mg) Carpuject Sterile
Cartridge unit with Luer Lock, box of 1, NDC 0409-2339-34. Store between 2��and 30��C
(36��and 86��F). Protect from freezing. Protect syringe from
light. Note: To prevent needle-stick injuries, needles and blunt cannulas should
not be recapped, purposely bent, or broken by hand. Revised: February, 2007
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General:: Impaired Hepatic Function may diminish metabolism of labetalol injection. Following Coronary Artery Bypass Surgery In one uncontrolled study, patients with low cardiac indices and
elevated systemic vascular resistance following intravenous labetalol
experienced significant declines in cardiac output with little change
in systemic vascular resistance. One of these patients developed hypotension
following labetalol treatment. Therefore, use of labetalol should
be avoided in such patients. High-Dose Labetalol Administration of
up to 3 g/d as an infusion for up to 2 to 3 days has been anecdotally
reported; several patients experienced hypotension or bradycardia
(see DOSAGE AND ADMINISTRATION). Hypotension 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 injection. Therefore, the patient's
ability to tolerate an upright position should be established before
permitting any ambulation. Jaundice or Hepatic Dysfunction (see WARNINGS).<br/>Information for Patients:: The following information is intended to aid in the
safe and effective use of this medication. It is not a disclosure
of all possible adverse or intended effects. During and immediately
following (for up to 3 hours) labetalol injection, the patient should
remain supine. Subsequently, the patient should be advised on how
to proceed gradually tobecome ambulatory, and should be observed
at the time of first ambulation. When the patient
is started on labetalol hydrochloride tablets following adequate control
of blood pressure with labetalol hydrochloride injection, appropriate
directions for titration of dosage should be provided (see DOSAGE AND ADMINISTRATION). As with all drugs with beta-blocking activity, certain
advice to patients being treated with labetalol is warranted: While
no incident of the abrupt withdrawal phenomenon (exacerbation of angina
pectoris) has been reported with labetalol, dosing with labetalol
tablets should not be interrupted or discontinued without a physician's
advice. Patients being treated with labetalol tablets should consult
a physician at any signs or symptoms of impending cardiac failure
or hepatic dysfunction (see WARNINGS). Also, transient scalp tingling may occur, usually when treatment
with labetalol tablets is initiated (see ADVERSE REACTIONS).<br/>Laboratory Tests:: Routine laboratory tests are ordinarily not required
before or after intravenous labetalol. In patients with concomitant
illnesses, such as impaired renal function, appropriate tests should
be done to monitor these conditions.<br/>Drug Interactions:: Since labetalol injection may be administered to
patients already being treated with other medications, including other
antihypertensive agents, careful monitoring of these patients is necessary
to detect and treat promptly any undesired effect from concomitant
administration. In one survey, 2.3% of patients
taking labetalol orally in combination with tricyclic antidepressants
experienced tremor as compared to 0.7% reported to occur with labetalol
alone. The contribution of each of the treatments to this adverse
reaction is unknown but the possibility of a drug interaction cannot
be excluded. Drugs possessing beta-blocking
properties can blunt the bronchodilator effect of beta-receptor agonist
drugs in patients with bronchospasm; therefore, doses greater than
the normal antiasthmatic dose of beta-agonist bronchodilator drugs
may be required. Cimetidine has been shown to
increase the bioavailability of labetalol administered orally. Since
this could be explained either by enhanced absorption or by an alteration
of hepatic metabolism of labetalol, special care should be used in
establishing the dose required for blood pressure control in such
patients. Synergism has been shown between halothane
anesthesia and intravenously administered labetalol. During controlled
hypotensive anesthesia using labetalol in association with halothane,
high concentrations (3% or above) of halothane should not be used
because the degree of hypotension will be increased and because of
the possibility of a large reduction in cardiac output and an increase
in central venous pressure. The anesthesiologist should be informed
when a patient is receiving labetalol. Labetalol
blunts the reflex tachycardia produced by nitroglycerin without preventing
its hypotensive effect. If labetalol is used with nitroglycerin in
patients with angina pectoris, additional antihypertensive effects
may occur. Care should be taken if labetalol
is used concomitantly with calcium antagonists of the verapamil type. When drug products that are alkaline, such as furosemide,
have been administered in combination with labetalol, a white precipitate
has been noted. Therefore, these drugs should not be administered
in the same infusion line. Risk of Anaphylactic Reaction While
taking beta-blockers, patients with a history of severe anaphylactic
reactions to a variety of allergens may be more reactive to repeated
challenge, either accidental, diagnostic, or therapeutic. Such patients
may be unresponsive to the usual doses of epinephrine used to treat
allergic reaction.<br/>Drug/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 (VMA) when measured by
fluorimetric or photometric methods. In screening patients suspected
of having a pheochromocytoma and being treated with labetalol, 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 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.<br/>Carcinogenesis, Mutagenesis,
Impairment of Fertility:: Long-term oral dosing studies with labetalol for
18 months in mice and for 2 years in rats showed no evidence of carcinogenesis.
Studies with labetalol, using dominant lethal assays in rats and mice,
and exposing microorganisms according to modified Ames tests, showed
no evidence of mutagenesis.<br/>Pregnancy: Teratogenic Effects : Pregnancy Category
C: Teratogenic studies have been performed with labetalol
in rats and rabbits at oral doses up to approximately 6 and 4 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
for hypertension during pregnancy. Oral administration of labetalol
to rats during late gestation through weaning at doses of 2 to 4 times
the MRHD caused a decrease in neonatal survival.<br/>Labor and Delivery:: Labetalol given to pregnant women with hypertension
did not appear to affect the usual course of labor and delivery.<br/>Nursing Mothers:: Small amounts of labetalol (approximately 0.004%
of the maternal dose) are excreted in human milk. Caution should be
exercised when labetalol injection is administered to a nursing woman.<br/>Pediatric Use:: Safety and effectiveness in children have not been
established.
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Overdosage with labetalol injection causes excessive
hypotension that is posture sensitive, and sometimes, excessive bradycardia.
Patients should be placed supine and their legs raised if necessary
to improve the blood supply to the brain. If overdosage with labetalol
follows oral ingestion, gastric lavage or pharmacologically induced
emesis (using syrup of ipecac) may be useful for removal of the drug
shortly after ingestion. The following additional measures should
be employed if necessary: Excessive bradycardia-administer atropine or epinephrine. Cardiac failure-administer a digitalis glycoside and a
diuretic. Dopamine or dobutamine may also be useful. Hypotension-administer vasopressors,
e.g., norepinephrine. There is pharmacological evidence that norepinephrine
may be the drug of choice. Bronchospasm-administer epinephrine and/or an aerosolized beta-agonist. Seizures-administer diazepam. In severe beta-blocker overdose resulting in hypotension
and/or bradycardia, glucagon has been shown to be effective when administered
in large doses (5 to 10 mg rapidly over 30 seconds, followed by continuous
infusion of 5 mg/hr that can be reduced as the patient improves). Neither hemodialysis nor peritoneal dialysis removes a
significant amount of labetalol from the general circulation (<1%). The oral LDvalue of labetalol in the mouse
is approximately 600 mg/kg and in the rat is greater than 2 g/kg.
The intravenous LDin these species is 50 to 60 mg/kg.
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Labetalol Hydrochloride
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Labetalol Hydrochloride (Injection, Solution)
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Labetalol injection is usually well tolerated. Most
adverse effects have been mild and transient and in controlled trials
involving 92 patients did not require labetalol 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 labetalolinjection. 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 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 7; hypoesthesia (numbness) and vertigo,
1 each. Gastrointestinal
System Nausea in 13; vomiting 4; dyspepsia and taste distortion,
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.
The largest experience is with oral labetalol. Certain of the side
effects increased with increasing oral dose as shown in the table
below which depicts the entire U.S. therapeutic trials data base for
adverse reactions that are clearly or possibly dose related. 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 during investigational
use and extensive foreign marketing experience. Clinical Laboratory Tests: Among
patients dosed with labetalol 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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Hepatic Injury Severe hepatocellular injury, confirmed by rechallenge in at least
one case, occurs rarely with labetalol therapy. The hepatic injury
is usually reversible, but hepatic necrosis and death have been reported.
Injury has occurred after both short- and long-term treatment and
may be slowly progressive despite minimal symptomatology. Similar
hepatic events have been reported with a related compound, dilevalol
HCl, including two deaths. Dilevalol HCl is one of the four isomers
of labetalol. Thus, for patients taking labetalol, periodic determination
of suitable hepatic laboratory tests would be appropriate. Laboratory
testing should also be done at the very first symptom or sign of liver
dysfunction (e.g., pruritus, dark urine, persistent anorexia, jaundice,
right upper quadrant tenderness, or unexplained���flu-like���symptoms). If the patient has jaundice or laboratory evidence of liver
injury, labetalol should be stopped and not restarted. Cardiac Failure Sympathetic stimulation is a vital component supporting circulatory
function in congestive heart failure. Beta-blockade carries a potential
hazard of further depressing myocardial contractility and precipitating
more severe failure. Although beta-blockers should be avoided in overt
congestive heart failure, if necessary, labetalol can be used with
caution in patients with a history of heart failure, who are well
compensated. Congestive heart failure has been observed in patients
receiving labetalol. Labetalol does not abolish the inotropic action
of digitalis on heart muscle. In Patients Without a History of Cardiac Failure In patients with latent cardiac insufficiency, continued depression
of the myocardium with beta-blocking agents over a period of time
can lead, in some cases, to cardiac failure. At the first sign or
symptom of impending cardiac failure, patients should be fully digitalized
and/or be given a diuretic, and the response observed closely. If
cardiac failure continues, despite adequate digitalization and diuretic,
labetalol therapy should be withdrawn (gradually if possible). Ischemic Heart Disease Angina pectoris has not been reported upon labetalol discontinuation.
However, following abrupt cessation of therapy with some beta-blocking
agents in patients with coronary artery disease, exacerbations of
angina pectoris and, in some cases, myocardial infarction have been
reported. Therefore, such patients should be cautioned against interruption
of therapy without the physician's advice. Even in the absence
of overt angina pectoris, when discontinuation of labetalol is planned,
the patient should be carefully observed and should be advised to
limit physical activity. If angina markedly worsens or acute coronary
insufficiency develops, labetalol administration should be reinstituted
promptly, at least temporarily, and other measures appropriate for
the management of unstable angina should be taken. Nonallergic Bronchospasm (e.g.,
chronic bronchitis and emphysema) Since labetalol injection at the
usual intravenous therapeutic doses has not been studied in patients
with nonallergic bronchospastic disease, it should not be used in
such patients. Pheochromocytoma Intravenous labetalol has been shown to
be effective in lowering the blood pressure and relieving symptoms
in patients with pheochromocytoma; higher than usual doses may be
required. However, paradoxical hypertensive responses have been reported
in a few patients with this tumor; therefore, use caution when administering
labetalol to patients with pheochromocytoma. Diabetes Mellitus and Hypoglycemia Beta-adrenergic blockade may prevent the appearance of premonitory
signs and symptoms (e.g., tachycardia) of acute hypoglycemia. This
is especially important with labile diabetics. Beta-blockade also
reduces the release of insulin in response to hyperglycemia; it may
therefore be necessary to adjust the dose of antidiabetic drugs. Major Surgery The
necessity or desirability of withdrawing beta-blocking therapy prior
to major surgery is controversial. Protracted severe hypotension and
difficulty in restarting or maintaining a heartbeat have been reported
with beta-blockers. The effect of labetalol's alpha-adrenergic
activity has not been evaluated in this setting. Several deaths have occurred when labetalol injection was used during
surgery (including when used in cases to control bleeding). A synergism between labetalol and halothane anesthesia
has been shown (see PRECAUTIONS - Drug Interactions). Rapid Decreases
of Blood Pressure Caution must be observed when reducing
severely elevated blood pressure. A number of adverse reactions, including
cerebral infarction, optic nerve infarction, angina, and ischemic
changes in the electrocardiogram, have been reported with other agents
when severely elevated blood pressure was reduced over time courses
of several hours to as long as 1 or 2 days. The desiredblood
pressure lowering should therefore be achieved over as long a period
of time as is compatible with the patient's status.
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Labetalol HCl injection is indicated for control
of blood pressure in severe hypertension.
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Labetalol Hydrochloride
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