DOXAZOSIN MESYLATE

DOXAZOSIN MESYLATe
(dox-a'zo-sin)
Cardura
Classifications: alpha-adrenergic antagonist;
Therapeutic: antihypertensive

Prototype: Prazosin
Pregnancy Category: B

Availability

1 mg, 2 mg, 4 mg, 8 mg tablets

Action

By selective competitive inhibition of alpha1-adrenoreceptors, it produces vasodilation in both arterioles and veinous vessels with the result that both peripheral vascular resistance and blood pressure are reduced.

Therapeutic Effect

Long-acting effect of lowering blood pressure in supine or standing individuals with most pronounced effect on diastolic pressure.

Uses

Mild to moderate hypertension, benign prostatic hypertrophy.

Unlabeled Uses

CHF.

Contraindications

Hypersensitivity to doxazosin, prazosin, and terazosin; hypotension, syncope. Safe use in children is not established.

Cautious Use

Hepatic impairment or disease; renal disease, impairment, or failure; pregnancy (category B); lactation.

Route & Dosage

Hypertension
Adult: PO Start with 1 mg h.s. and titrate up to maximum of 16 mg/d in 1–2 divided doses
Geriatric: PO Start with 0.5 mg h.s.

Administration

Oral
  • Give initial dose at bedtime to minimize problems with postural hypotension and syncope.
  • Individualize maintenance dose according to the standing BP response.
  • Store at 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

CV: Orthostatic hypotension, edema. CNS: Vertigo, headache, dizziness, somnolence, fatigue, nervousness, anxiety. GI: Nausea, abdominal pain. Hematologic: Leukopenia. Skin: Pruritus, eczema.

Interactions

Drug: Sildenafil, vardenafil, and tadalafil may enhance hypotensive effects.

Pharmacokinetics

Absorption: Readily absorbed from GI tract; 62–69% of dose reaches systemic circulation. Peak: 2–6 h. Duration: Up to 24 h. Distribution: Highly protein bound (98–99%). Metabolism: Approximately 35% of dose is metabolized in liver. Elimination: 9% in urine, 63% in feces. Half-Life: 9–12 h.

Nursing Implications

Assessment & Drug Effects

  • Monitor BP with patient lying down and standing; doses above 4 mg increase the risk of postural hypotension.
  • Monitor BP 2–6 h after initial dose or any dose increase. This is when postural hypotension is most likely to occur.

Patient & Family Education

  • Do not drive or engage in other potentially hazardous activities for 12–24 h after the first dose or an increase in dosage or when medication is restarted after an interruption in dosage.
  • Use caution when rising from a sitting or supine position in order to avoid orthostatic hypotension and syncope; make position and directional changes slowly and in stages.
  • Report to the physician episodes of dizziness or palpitations. These will require a dosage adjustment.

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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