Labetalol Hydrochloride: Package Insert and Label Information
LABETALOL HYDROCHLORIDE- labetalol hydrochloride injection
Almaject, Inc.
DESCRIPTION
Labetalol hydrochloride injection is an adrenergic receptor blocking agent that has both selective alpha1 -adrenergic and nonselective beta-adrenergic receptor blocking actions in a single substance.
Labetalol hydrochloride (HCl) is a racemate chemically designated as 2-hydroxy-5-[1-hydroxy-2-[(1-methyl-3-phenylpropyl)amino]ethyl]benzamide monohydrochloride, and it has the following structure:
Labetalol HCl has the empirical formula C19 H24 N2 O3 •HCl and a molecular weight of 364.9. 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 HCl 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 (IV) injection. It has a pH range of 3.0 to 4.5. Each mL contains 5 mg labetalol hydrochloride USP, 45 mg anhydrous dextrose, 0.10 mg edetate disodium; 0.80 mg of methylparaben and 0.10 mg of propylparaben as preservatives; and citric acid monohydrate and sodium hydroxide, as necessary, to bring the solution into the pH range.
CLINICAL PHARMACOLOGY
Labetalol HCl combines both selective, competitive, alpha1 -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. Beta2 -agonist activity has been demonstrated in animals with minimal beta1 -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 HCl to block alpha receptors in man has been demonstrated by attenuation of the pressor effect of phenylephrine and by a significant reduction of the pressor response caused by immersing the hand in ice-cold water (“cold-pressor test”). Labetalol HCl’s beta1 -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. Beta2 -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 HCl contribute to a decrease in blood pressure in hypertensive patients. Labetalol HCl consistently, in dose-related fashion, blunted increases in exercise-induced blood pressure and heart rate, and in their double product. The pulmonary circulation during exercise was not affected by labetalol HCl dosing.
Single oral doses of labetalol HCl administered to patients with coronary artery disease had no significant effect on sinus rate, intraventricular conduction, or QRS duration. The atrioventricular (A-V) conduction time was modestly prolonged in two of seven patients. In another study, intravenous labetalol HCl slightly prolonged A-V nodal conduction time and atrial effective refractory period with only small changes in heart rate. The effects on A-V nodal refractoriness were inconsistent.
Labetalol HCl produces dose-related falls in blood pressure without reflex tachycardia and without significant reduction in heart rate, presumably through a mixture of its alpha- 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 HCl that controlled hypertension did not affect renal function in mildly to severely hypertensive patients with normal renal function.
Due to the alpha1 -receptor blocking activity of labetalol HCl, 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 HCl, the contribution of the postural component should be considered when positioning the patient for treatment, and the patient should not be allowed to move to an erect position unmonitored until this ability to do so is established.
In a clinical pharmacologic study in severe hypertensives, an initial 0.25 mg/kg injection of labetalol HCl 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 HCl 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 HCl, 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 who required 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 mg or 80 mg at 10 minute intervals to achieve the desired effect, or up to a cumulative dose of 300 mg.
Labetalol HCl administered as a continuous intravenous infusion, with a mean dose of 136 mg (27 mg 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 A-V block by preventing the necessary facilitating effects of sympathetic activity on conduction. Beta2 -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 of labetalol, the elimination half-life is about 5.5 hours and the total body clearance is approximately 33 mL/min per kilogram. 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. The 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 HCl from the general circulation (<1%).
INDICATIONS AND USAGE
Labetalol hydrochloride injection is indicated for control of blood pressure in severe hypertension.
CONTRAINDICATIONS
Labetalol hydrochloride 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.
WARNINGS
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 research compound, dilevalol HCl, including two deaths. Dilevalol HCl is one of the four isomers of labetalol HCl. Thus, for patients taking labetalol, periodic determination of suitable hepatic laboratory tests would be appropriate. Appropriate laboratory testing should be done at the first symptom/sign of liver dysfunction (e.g., pruritus, dark urine, persistent anorexia, jaundice, right upper quadrant tenderness, or unexplained “flulike” symptoms). If the patient has laboratory evidence of liver injury or jaundice, 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 HCl. Labetalol HCl 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, in some cases, lead 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 should be observed closely. If cardiac failure continues despite adequate digitalization and diuretic, therapy with labetalol hydrochloride injection should be withdrawn (gradually, if possible).
Ischemic Heart Disease
Angina pectoris has not been reported upon labetalol HCl 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 hydrochloride injection 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, administration of labetalol hydrochloride injection 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 hydrochloride 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 HCl has been shown to be effective in lowering 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 HCl 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
Do not routinely withdraw chronic beta blocker therapy prior to surgery. The effect of labetalol’s alpha adrenergic activity has not been evaluated in this setting.
Several deaths have occurred when labetalol hydrochloride injection was used during surgery (including when used in cases to control bleeding).
A synergism between labetalol HCl 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 desired blood pressure lowering should therefore be achieved over as long a period of time as is compatible with the patient’s status.
PRECAUTIONS
General
Impaired Hepatic Function: Labetalol hydrochloride injection should be used with caution in patients with impaired hepatic function since metabolism of the drug may be diminished.
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 hydrochloride injection. Therefore, the patient’s ability to tolerate an upright position should be established before permitting any ambulation.
Intraoperative Floppy Iris Syndrome (IFIS) has been observed during cataract surgery in some patients treated with alpha-1 blockers (labetalol is an alpha/beta blocker). This variant of small pupil syndrome is characterized by the combination of a flaccid iris that billows in response to intraoperative irrigation currents, progressive intraoperative miosis despite preoperative dilation with standard mydriatic drugs, and potential prolapse of the iris toward the phacoemulsification incisions. The patient’s ophthalmologist should be prepared for possible modifications to the surgical technique, such as the utilization of iris hooks, iris dilator rings, or viscoelastic substances. There does not appear to be a benefit of stopping alpha-1 blocker therapy prior to cataract surgery.
Following Coronary Artery Bypass Surgery: In one uncontrolled study, patients with low cardiac indices and elevated systemic vascular resistance following intravenous labetalol HCl 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 HCl 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 have experienced hypotension or bradycardia.
Jaundice or Hepatic Dysfunction: (see WARNINGS).
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 hydrochloride injection, the patient should remain supine. Subsequently, the patient should be advised on how to proceed gradually to become 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 HCl is warranted. While no incident of the abrupt withdrawal phenomenon (exacerbation of angina pectoris) has been reported with labetalol HCl, dosing with labetalol hydrochloride tablets should not be interrupted or discontinued without a physician’s advice. Patients being treated with labetalol hydrochloride 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 hydrochloride tablets is initiated (see ADVERSE REACTIONS).
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