GUANABENZ ACETATE
| GUANABENZ ACETATE (gwan'a-benz) Wytensin Classifications: alpha-adrenergic agonist; central-acting antihypertensive; Therapeutic: antihypertensive Prototype: Methyldopa Pregnancy Category: C |
Availability
4 mg, 8 mg tablets
Action
Centrally acting alpha2-adrenergic agonist. Pharmacologic actions closely resemble those of clonidine. Lowers BP, primarily by stimulating central alpha-adrenergic receptors that lead to inhibition of sympathetic outflow from brain. Has no effect on exercise tolerance or on potassium levels.
Therapeutic Effect
Reduces both supine and standing BP, usually without producing postural hypotension, and slightly lowers pulse rate. Given the fact that central adrenergic hyperactivity causes symptoms of narcotic withdrawal, guanabenz appears to help control abstinence symptoms by reducing norepinephrine output.
Uses
Used alone in treatment of hypertension or in combination with a thiazide diuretic.
Unlabeled Uses
Opiate detoxification, analgesic for chronic pain.
Contraindications
Pregnancy (category C), lactation. Safe use in children is not established.
Cautious Use
Severe coronary insufficiency, recent MI, cerebrovascular disease, severe hepatic or renal failure; older adults; concurrent use of MAOI therapy.
Route & Dosage
| Hypertension Adult: PO 4 mg b.i.d., may increase by 4–8 mg/d q1–2wk up to 32 mg b.i.d. Geriatric: PO 4 mg once daily, may increase every 1–2 wk Opiate Withdrawal Adult: PO 4 mg b.i.d. to q.i.d. |
Administration
Oral- Give one dose at bedtime to ensure overnight control and reduce possibility of daytime drowsiness or sedation.
- Store at 15°–30° C (59°–86° F) in tightly closed containers unless otherwise directed.
Adverse Effects (≥1%)
CNS: Drowsiness or sedation, dizziness, weakness, headache, anxiety, ataxia, depression, sleep disturbances, somnolence. CV: Chest pain, edema, arrhythmias, palpitation, hypotension, bradycardia, nervousness. GI: Dry mouth, nausea, epigastric pain, diarrhea, vomiting, constipation, abdominal discomfort, taste disorders. Urogenital: Increased urination, urinary frequency, sexual dysfunction. Special Senses: Blurred vision, miosis, nasal congestion. Body as a Whole: Dyspnea, muscle aches, aches in extremities, lethargy, irritability, unusual fatigue or weakness. Skin: Rash, pruritus.Interactions
Drug: Alcohol and other cns depressants compound CNS depression; tricyclic antidepressants may reduce antihypertensive effects of guanabenz.Pharmacokinetics
Absorption: 75% absorbed from GI tract. Onset: 60 min. Peak: 2–5 h. Duration: 6–12 h. Distribution: Widely distributed; crosses blood–brain barrier; not known if crosses placenta or distributed into breast milk. Metabolism: Extensively metabolized. Elimination: 80% in urine; 20% in feces. Half-Life: 4–14 h.Nursing Implications
Assessment & Drug Effects
- Monitor BP and HR. Report palpitations or hypotension to physician.
- Evaluate mental status and alertness.
- Lab tests: Baseline and periodic blood chemistry (serum potassium, CBC, creatinine, uric acid, cholesterol, glucose), urinalysis for protein and sugar, and ECG.
- Give early attention and specific treatment to dry mouth. It can interfere with patient's food and fluid intake; deprivation of normal salivary flow is a potential dental hazard since it favors demineralization of teeth; and it can be a factor in noncompliance.
Patient & Family Education
- Make all position changes slowly and in stages in the event that you experience orthostatic hypotension. This is important in older adults, who tend to be more sensitive to normal adult doses of antihypertensive drugs because of deficient baroreceptor reflexes.
- Do not omit a dose or stop drug therapy without consulting physician. Do not discontinue therapy abruptly; can cause sympathetic overactivity (anxiety, nervousness, palpitation, chest pain, fast or irregular heartbeat, trembling, flushing, headache, increased sweating and salivation, elevation of BP, usually above basal level).
- Do not drive or engage in potentially hazardous activities until response to drug is known. Also, guanabenz may reduce tolerance to alcohol and other CNS depressants.
Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; 
Canadian drug name; 
Prototype drug