labetalol hydrochloride

labetalol hydrochloride

(la bet' a lol)

Normodyne, Trandate

Pregnancy Category C

Drug classes

Alpha- and beta-adrenergic blocker

Antihypertensive

Therapeutic actions

Competitively blocks alpha₁- and beta₁- and beta₂-adrenergic receptors, and has some sympathomimetic activity at beta₂-receptors. Alpha- and beta-blocking actions contribute to the BP-lowering effect; beta blockade prevents the reflex tachycardia seen with most alpha-blocking drugs and decreases plasma renin activity.

Indications

·        Hypertension, alone or with other oral drugs, especially diuretics

·        Parenteral preparations: Severe hypertension

·        Unlabeled uses: Control of BP in pheochromocytoma; clonidine withdrawal hypertension

Contraindications and cautions

·        Contraindicated with sinus bradycardia, second or third-degree heart block, cardiogenic shock, CHF, asthma.

·        Use cautiously with diabetes or hypoglycemia (can mask cardiac signs of hypoglycemia), nonallergic bronchospasm (oral drug—IV is absolutely contraindicated), pheochromocytoma (paradoxical increases in BP have occurred), pregnancy, lactation.

Available forms

Tablets—100, 200, 300 mg; injection—5 mg/mL

Dosages

ADULTS

Oral

Initial dose 100 mg bid. After 2–3 days, using standing BP as indicator, adjust dosage in increments of 100 mg bid q 2–3 days. For maintenance, 200–400 mg bid. Up to 2,400 mg/day may be required; to improve tolerance, divide total daily dose and give tid.

Parenteral

·        Severe hypertension: For repeated IV injection, 20 mg (0.25 mg/kg) slowly over 2 min. Individualize dosage using supine BP; additional doses of 40 or 80 mg can be given at 10-min intervals until desired BP is achieved or until a 300-mg dose has been injected. For continuous IV infusion, dilute ampule (see IV facts), infuse at the rate of 2 mg/min, adjust according to BP response up to 300 mg total dose. Transfer to oral therapy as soon as possible.

PEDIATRIC PATIENTS

Safety and efficacy not established.

GERIATRIC PATIENTS

Generally require lower maintenance doses.

Pharmacokinetics

Route	Onset	Peak	Duration
Oral	Varies	1–2 hr	8–12 hr
IV	Immediate	5 min	5.5 hr

Metabolism: Hepatic; T_1/2: 6–8 hr

Distribution: Crosses placenta; enters breast milk

Excretion: Urine

IV facts

Preparation: Add 200 mg to 160 mL of a compatible IV fluid to make a 1 mg/mL solution; infuse at 2 mL/min, or add 200 mg (2 ampules) to 250 mg of IV fluid to make a 2 mg/3 mL solution, infuse at 3 mL/min. Compatible IV fluids include Ringer's, lactated Ringer's, 0.9% sodium chloride, 2.5% dextrose and 0.45% sodium chloride, 5% dextrose, 5% dextrose and Ringer's, 5% dextrose and 5% lactated Ringer's, and 5% dextrose and 0.2%, 0.33%, or 0.9% sodium chloride. Stable for 24 hr in these solutions at concentrations between 1.25 and 3.75 mg/mL.

Infusion: Administer infusion at 2–3 mL/min; inject slowly over 2 min.

Incompatibilities: Do not dilute drug in 5% sodium bicarbonate injection or other alkaline solutions, including furosemide.

Y-site incompatibilities: Do not give with cefoperazone, nafcillin.

Adverse effects

·        CNS: Dizziness, vertigo, fatigue, depression, paresthesias, sleep disturbances, hallucinations, disorientation, memory loss, slurred speech

·        CV: CHF, cardiac arrhythmias, peripheral vascular insufficiency, claudication, CVA, pulmonary edema, hypotension

·        Dermatologic: Rash, pruritus, sweating, dry skin

·        EENT: Eye irritation, dry eyes, conjunctivitis, blurred vision

·        GI: Gastric pain, flatulence, constipation, diarrhea, nausea, vomiting, anorexia, ischemic colitis, renal and mesenteric arterial thrombosis, retroperitoneal fibrosis, hepatomegaly, acute pancreatitis

·        GU: Impotence, decreased libido, Peyronie's disease, dysuria, nocturia, polyuria, priapism, urinary retention

·        Respiratory: Bronchospasm, dyspnea, cough, bronchial obstruction, nasal stuffiness, rhinitis, pharyngitis

·        Other: Decreased exercise tolerance, development of antinuclear antibodies, hyperglycemia or hypoglycemia, elevated liver enzymes

Interactions

Drug-drug

·        Risk of excessive hypotension with enflurane, halothane, or isoflurane

·        Potential for added anithypertensive effects with nitroglycerin

·        Additive A-V block with calcium channel-blockers

Drug-lab test

·        Possible falsely elevated urinary catecholamines in lab tests using a trihydroxyindole reaction

Nursing considerations

Assessment

·        History: Sinus bradycardia, second- or third-degree heart block, cardiogenic shock, CHF, asthma, pregnancy, lactation, diabetes or hypoglycemia,nonallergic bronchospasm, pheochromocytoma

·        Physical: Weight, skin condition, neurologic status, P, BP, ECG, respiratory status, renal and thyroid function, blood and urine glucose

Interventions

·        WARNING: Do not discontinue drug abruptly after long-term therapy. (Hypersensitivity to catecholamines may have developed, causing exacerbation of angina, MI and ventricular arrhythmias; taper drug gradually over 2 wk with monitoring.)

·        Consult with physician about withdrawing the drug if the patient is to undergo surgery (withdrawal is controversial).

·        Keep patient supine during parenteral therapy, and assist initial ambulation.

·        Position to decrease effects of edema.

·        Provide support and encouragement to deal with drug effects and disease.

Teaching points

·        Take drug with meals.

·        Do not stop taking unless instructed to do so by a health care provider.

·        If you have diabetes, monitor your blood glucose carefully. This drug may mask usual symptoms of hypoglycemia.

·        You may experience these side effects: Dizziness, light-headedness, loss of appetite, nightmares, depression, sexual impotence.

·        Report difficulty breathing, night cough, swelling of extremities, slow pulse, confusion, depression, rash, fever, sore throat.

Adverse effects in Italic are most common; those in Bold are life-threatening.