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.
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.
In addition, a number of other less common adverse events have been reported:
Body as a Whole
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.
Systemic lupus erythematosus, positive antinuclear factor.
Liver and Biliary System
Hepatic necrosis, hepatitis, cholestatic jaundice, elevated liver function tests.
Muscle cramps, toxic myopathy.
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.
Difficulty in micturition, including acute urinary bladder retention.
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.
Intensification of A-V block (see CONTRAINDICATIONS).
Fever combined with aching and sore throat, laryngospasm, respiratory distress.
Agranulocytosis, thrombocytopenic or nonthrombocytopenic purpura.
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.
Overdosage with labetalol hydrochloride 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 hydrochloride 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:
Administer atropine or epinephrine.
Administer a digitalis glycoside and a diuretic. Dopamine or dobutamine may also be useful.
Administer vasopressors, e.g., norepinephrine. There is pharmacologic evidence that norepinephrine may be the drug of choice.
Administer epinephrine and/or an aerosolized beta2 -agonist.
In severe beta-blocker overdose resulting in hypotension and/or bradycardia, glucagon has been shown to be effective when administered in large doses (5 mg to 10 mg rapidly over 30 seconds, followed by continuous infusion of 5 mg per hour that can be reduced as the patient improves).
Neither hemodialysis nor peritoneal dialysis removes a significant amount of labetalol hydrochloride from the general circulation (less than 1%).
The oral LD50 value of labetalol hydrochloride in the mouse is approximately 600 mg/kg and in the rat is greater than 2 g/kg. The intravenous LD50 in these species is 50 mg/kg to 60 mg/kg.
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, USP is between 200 mg and 400 mg twice daily.
Since the full antihypertensive effect of labetalol hydrochloride tablets, USP 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 tablets, USP dosage adjustment. As with most antihypertensive drugs, optimal dosages of labetalol hydrochloride tablets, USP are usually lower in patients also receiving a diuretic.
When transferring patients from other antihypertensive drugs, labetalol hydrochloride tablets, USP should be introduced as recommended and the dosage of the existing therapy progressively decreased.
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).
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