LABETALOL HYDROCHLORIDE

LABETALOL HYDROCHLORIDE
(la-bet'a-lole)
Trandate
Classifications: alpha- & beta-adrenergic antagonist; antihypertensive agent;
Therapeutic: antihypertensive

Prototype: Propranolol
Pregnancy Category: B first and second trimester; D third trimester

Availability

100 mg, 200 mg, 300 mg tablet; 5 mg/mL injection

Action

Acts as an adrenergic receptor blocking agent that combines selective alpha activity and nonselective beta-adrenergic blocking actions. The alpha blockade results in vasodilation, decreased peripheral resistance, and orthostatic hypotension and only slightly affects cardiac output and coronary artery blood flow. It has beta-blocking effects on the sinus node, AV node, and ventricular muscle, which lead to bradycardia, delay in AV conduction, and depression of cardiac contractility.

Therapeutic Effect

Effective in reducing blood pressure by vasodilation as well as depression of cardiac contractility.

Uses

Mild, moderate, and severe hypertension. May be used alone or in combination with other anti-hypertensive agents, especially thiazide diuretics.

Contraindications

NSAID or salicylate hypersensitivity; bronchial asthma; uncontrolled cardiac failure, heart block (greater than first degree), cardiogenic shock, severe bradycardia; perioperative CABG pain; pregnancy (category B in first and second trimester and category D in third trimester). Safe use in children is not established.

Cautious Use

Nonallergic bronchospastic disease (COPD); renal disease, renal failure, hepatic disease; well-compensated patients with history of heart failure; acute MI; coronary artery disease; pheochromocytoma; impaired liver function, jaundice; diabetes mellitus; SLE; peripheral vascular disease.

Route & Dosage

Hypertension
Adult: PO 100 mg b.i.d., may gradually increase to 200–400 mg b.i.d. (max: 1200–2400 mg/d). IV 20 mg slowly over 2 min, with 40–80 mg q10min if needed up to 300 mg total or 2 mg/min continuous infusion (max: 300 mg total dose)
Geriatric: PO Start with 100 mg daily IV 20 mg slowly over 2 min, with 40–80 mg q10min if needed up to 300 mg total or 2 mg/min continuous infusion (max: 300 mg total dose)

Administration

Oral
  • Give with or immediately after food consistently. Food increases drug bioavailability.
Intravenous
  • Note: Amount of IV solution may be changed depending on patient status.

PREPARE: Direct: Give undiluted.  Continuous: Dilute 300 mg in 240 of D5W, NS, D5/NS, RL, or other compatible IV solution to yield 1 mg/mL.  

ADMINISTER: Direct: Give a 20-mg dose slowly over 2 min. Maximum hypotensive effect occurs 5–15 min after each administration.  Continuous: Normal rate is 2 mg/min. Keep patient supine when receiving labetalol IV. Take BP immediately before administration. Rate is adjusted according to BP response. Discontinue drug once the desired BP is attained.  

INCOMPATIBILITIES Solution/additive: Sodium bicarbonate, ceftriaxone, tenecteplase. Y-site: Amphotericin B cholesteryl, cefoperazone, furosemide, heparin, nafcillin, thiopental, warfarin.

  • Controlled infusion pump device is recommended for maintaining accurate flow rate during IV infusion. Usually administered at rate of 2 mg/min.
  • Store at 2°–30° C (36°–86° F) unless otherwise advised. Do not freeze. Protect tablets from moisture.

Adverse Effects (≥1%)

CNS: Dizziness, fatigue/malaise, headache, tremors, transient paresthesias (especially scalp tingling), hypoesthesia (numbness) following IV, mental depression, drowsiness, sleep disturbances, nightmares. CV: Postural hypotension, angina pectoris, palpitation, bradycardia, syncope, pedal or peripheral edema, pulmonary edema, CHF, flushing, cold extremities, arrhythmias (following IV), paradoxical hypertension (patients with pheochromocytoma). Special Senses: Dry eyes, vision disturbances, nasal stuffiness, rhinorrhea. GI: Nausea, vomiting, dyspepsia, constipation, diarrhea, taste disturbances, cholestasis with or without jaundice, increases in serum transaminases, dry mouth. Urogenital: Acute urinary retention, difficult micturition, impotence, ejaculation failure, loss of libido, Peyronie's disease. Respiratory: Dyspnea, bronchospasm. Skin: Rashes of various types, increased sweating, pruritus. Body as a Whole: Myalgia, muscle cramps, toxic myopathy, antimitochondrial antibodies, positive antinuclear antibodies (ANA), SLE syndrome, pain at IV injection site.

Diagnostic Test Interference

False increases in urinary catecholamines when measured by nonspecific trihydroxyindole (THI) reaction (due to labetalol metabolites) but not with specific radioenzymatic or high-performance liquid chromatography assay techniques.

Interactions

Drug: Cimetidine may increase effects of labetalol; glutethimide decreases effects of labetalol; halothane adds to hypotensive effects; may mask symptoms of hypoglycemia caused by oral sulfonylureas, insulin; beta agonists antagonize effects of labetalol.

Pharmacokinetics

Absorption: Readily from GI tract, only 25% reaches systemic circulation due to first pass metabolism. Onset: 20 min–2 h PO; 2–5 min IV. Peak: 1–4 h PO; 5–15 min IV. Duration: 8–24 h PO; 2–4 h IV. Distribution: Crosses placenta; distributed into breast milk. Metabolism: In liver (CYP2D6). Elimination: 60% in urine, 40% in bile. Half-Life: 3–8 h.

Nursing Implications

Assessment & Drug Effects

  • Monitor BP and pulse during dosage adjustment period. Use standing BP as indicator for making dosage adjustments for oral drugs and assessing patient's tolerance of dosage increases. Take after patient stands for 10 min. Clarify with physician.
  • Monitor BP at 5 min intervals for 30 min after IV administration; then at 30 min intervals for 2 h; then hourly for about 6 h; and as indicated thereafter.
  • Monitor diabetic patients closely; drug may mask usual cardiovascular response to acute hypoglycemia (e.g., tachycardia).
  • Convert from IV to PO therapy only when supine diastolic pressure rises about 10 mm Hg.
  • Maintain patient in supine position for at least 3 h after IV administration. Then determine patient's ability to tolerate elevated and upright positions before allowing ambulation. Manage this slowly.

Patient & Family Education

  • Note: Postural hypotension is most likely to occur during peak plasma levels (i.e., 2–4 h after drug administration).
  • Make all position changes slowly and in stages, particularly from lying to upright position. Older adult patients are especially sensitive to hypotensive effects.
  • Do not drive or engage in other potentially hazardous activities until response to drug is known.
  • Note: Most adverse effects (e.g., scalp tingling) are mild, transient, and dose related and occur early in therapy.
  • Be sure to keep follow-up appointments. Get liver and kidney function tests periodically during therapy.
  • Discontinue drug gradually over 1–2 wk period after chronic administration. Close monitoring during this time is very important.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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