labetalol

INDICATIONS AND USAGE Labetalol hydrochloride tablets, USP are indicated in the management of hypertension. Labetalol hydrochloride tablets, USP may be used alone or in combination with other antihypertensive agents, especially thiazide and loop diuretics.

DOSAGE AND ADMINISTRATION DOSAGE MUST BE INDIVIDUALIZED. The recommended initial dosage is 100 mg twice daily whether used alone or added to a diuretic regimen. After 2 or 3 days, using standing blood pressure as an indicator, dosage may be titrated in increments of 100 mg b.i.d. (twice daily) every 2 or 3 days. The usual maintenance dosage of labetalol hydrochloride tablets is between 200 mg and 400 mg twice daily. Since the full antihypertensive effect of labetalol hydrochloride tablets is usually seen within the first 1 to 3 hours of the initial dose or dose increment, the assurance of a lack of an exaggerated hypotensive response can be clinically established in the office setting. The antihypertensive effects of continued dosing can be measured at subsequent visits, approximately 12 hours after a dose, to determine whether further titration is necessary. Patients with severe hypertension may require from 1200 mg to 2400 mg per day, with or without thiazide diuretics. Should side effects (principally nausea or dizziness) occur with these doses administered b.i.d. (twice daily), the same total daily dose administered t.i.d. (three times daily) may improve tolerability and facilitate further titration. Titration increments should not exceed 200 mg b.i.d. (twice daily). When a diuretic is added, an additive antihypertensive effect can be expected. In some cases this may necessitate a labetalol hydrochloride tablet dosage adjustment. As with most antihypertensive drugs, optimal dosages of labetalol hydrochloride tablets are usually lower in patients also receiving a diuretic. When transferring patients from other antihypertensive drugs, labetalol hydrochloride tablets should be introduced as recommended and the dosage of the existing therapy progressively decreased. Elderly Patients As in the general patient population, labetalol therapy may be initiated at 100 mg twice daily and titrated upwards in increments of 100 mg b.i.d. (twice daily) as required for control of blood pressure. Since some elderly patients eliminate labetalol more slowly, however, adequate control of blood pressure may be achieved at a lower maintenance dosage compared to the general population. The majority of elderly patients will require between 100 mg and 200 mg b.i.d. (twice daily).

ADVERSE REACTIONS Most adverse effects are mild and transient and occur early in the course of treatment. In controlled clinical trials of 3 to 4 months’ duration, discontinuation of labetalol hydrochloride due to one or more adverse effects was required in 7% of all patients. In these same trials, other agents with solely beta- blocking activity used in the control groups led to discontinuation in 8% to 10% of patients, and a centrally acting alpha-agonist led to discontinuation in 30% of patients. The incidence rates of adverse reactions listed in the following table were derived from multicenter, controlled clinical trials comparing labetalol hydrochloride, placebo, metoprolol, and propranolol over treatment periods of 3 and 4 months. Where the frequency of adverse effects for labetalol hydrochloride and placebo is similar, causal relationship is uncertain. The rates are based on adverse reactions considered probably drug related by the investigator. If all reports are considered, the rates are somewhat higher (e.g., dizziness, 20%; nausea, 14%; fatigue, 11%), but the overall conclusions are unchanged. Labetalol Hydrochloride (N=227) % Placebo (N=98) % Propranolol (N=84) % Metoprolol (N=49) % Body as a whole Fatigue 5 0 12 12 Asthenia 1 1 1 0 Headache 2 1 1 2 Gastrointestinal Nausea 6 1 1 2 Vomiting less than 1 0 0 0 Dyspepsia 3 1 1 0 Abdominal pain 0 0 1 2 Diarrhea less than 1 0 2 0 Taste distortion 1 0 0 0 Central and Peripheral Nervous Systems Dizziness 11 3 4 4 Paresthesia less than 1 0 0 0 Drowsiness less than 1 2 2 2 Autonomic Nervous System Nasal stuffiness 3 0 0 0 Ejaculation failure 2 0 0 0 Impotence 1 0 1 3 Increased sweating less than 1 0 0 0 Cardiovascular Edema 1 0 0 0 Postural hypotension 1 0 0 0 Bradycardia 0 0 5 12 Respiratory Dyspnea 2 0 1 2 Skin Rash 1 0 0 0 Special Senses Vision abnormality 1 0 0 0 Vertigo 2 1 0 0 The adverse effects were reported spontaneously and are representative of the incidence of adverse effects that may be observed in a properly selected hypertensive patient population, i.e., a group excluding patients with bronchospastic disease, overt congestive heart failure, or other contraindications to beta-blocker therapy. Clinical trials also included studies utilizing daily doses up to 2400 mg in more severely hypertensive patients. Certain of the side effects increased with increasing dose, as shown in the following table that depicts the entire U.S. therapeutic trials data base for adverse reactions that are clearly or possibly dose related. Labetalol Hydrochloride 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 less than 1 0 1 2 4 0 7 11 19 Vomiting 0 0 less than 1 less than 1 less than 1 0 1 2 3 Dyspepsia 1 0 2 1 1 0 2 2 4 Paresthesias 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: Body as a Whole Fever. Cardiovascular Hypotension, and rarely, syncope, bradycardia, heart block. Central and Peripheral Nervous Systems Paresthesia, most frequently described as scalp tingling. In most cases, it was mild and transient and usually occurred at the beginning of treatment. Collagen Disorders Systemic lupus erythematosus, positive antinuclear factor. Eyes Dry eyes. Immunological System Antimitochondrial antibodies. Liver and Biliary System Hepatic necrosis, hepatitis, cholestatic jaundice, elevated liver function tests. Musculoskeletal System Muscle cramps, toxic myopathy. Respiratory System Bronchospasm. Skin and Appendages Rashes of various types, such as generalized maculopapular, lichenoid, urticarial, bullous lichen planus, psoriaform, and facial erythema; Peyronie’s disease, reversible alopecia. Urinary System Difficulty in micturition, including acute urinary bladder retention. Hypersensitivity Rare reports of hypersensitivity (e.g., rash, urticaria, pruritus, angioedema, dyspnea) and anaphylactoid reactions. Following approval for marketing in the United Kingdom, a monitored release survey involving approximately 6,800 patients was conducted for further safety and efficacy evaluation of this product. Results of this survey indicate that the type, severity, and incidence of adverse effects were comparable to those cited above. Potential Adverse Effects In addition, other adverse effects not listed above have been reported with other beta-adrenergic blocking agents. Central Nervous System Reversible mental depression progressing to catatonia, an acute reversible syndrome characterized by disorientation for time and place, short-term memory loss, emotional lability, slightly clouded sensorium, and decreased performance on psychometrics. Cardiovascular Intensification of A-V block [see Contraindications ] . Allergic Fever combined with aching and sore throat, laryngospasm, respiratory distress. Hematologic Agranulocytosis, thrombocytopenic or nonthrombocytopenic purpura. Gastrointestinal Mesenteric artery thrombosis, ischemic colitis. The oculomucocutaneous syndrome associated with the beta-blocker practolol has not been reported with labetalol hydrochloride. Clinical Laboratory Tests There have been reversible increases of serum transaminases in 4% of patients treated with labetalol hydrochloride and tested and, more rarely, reversible increases in blood urea.

Drug Interactions In one survey, 2.3% of patients taking labetalol hydrochloride in combination with tricyclic antidepressants experienced tremor, as compared to 0.7% reported to occur with labetalol hydrochloride 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 anti-asthmatic dose of beta-agonist bronchodilator drugs may be required. Cimetidine has been shown to increase the bioavailability of labetalol hydrochloride. Since this could be explained either by enhanced absorption or by an alteration of hepatic metabolism of labetalol hydrochloride, 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 hydrochloride. During controlled hypotensive anesthesia using labetalol hydrochloride 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 hydrochloride. Labetalol hydrochloride blunts the reflex tachycardia produced by nitroglycerin without preventing its hypotensive effect. If labetalol hydrochloride 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. Both digitalis glycosides and beta-blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia. Risk of Anaphylactic Reaction While taking beta-blockers, patients with a history of severe anaphylactic reaction 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.