GUANFACINE HYDROCHLORIDE
| GUANFACINE HYDROCHLORIDE (gwahn'fa-seen) Tenex Classifications: alpha-adrenergic agonist; central-acting antihypertensive; Therapeutic: antihypertensive Prototype: Methyldopa Pregnancy Category: B |
Availability
1 mg, 2 mg tablets
Action
Central-acting antihypertensive with alpha2-adrenergic agonist properties. In cerebral cortex, stimulation of alpha2-adrenoreceptors triggers inhibitory neurons to reduce central sympathetic outflow (i.e., impulses from vasomotor center to heart and blood vessels).
Therapeutic Effect
Results in decreased peripheral vascular resistance, thus lowering blood pressure, and a slightly reduced (5 bpm) heart rate.
Uses
Management of mild to moderate hypertension.
Unlabeled Uses
Adjunct in heroin withdrawal.
Contraindications
Treatment of acute hypertension associated with toxemia of pregnancy; children <12 y; lactation.
Cautious Use
Severe coronary insufficiency, recent MI, cerebrovascular disease; chronic renal or hepatic failure; older adult; pregnancy (category B).
Route & Dosage
| Hypertension Adult: PO 1 mg/d h.s., may be gradually increased to 3 mg/d if needed |
Administration
Oral- Take single dose at bedtime to reduce effect of somnolence.
- Discontinue treatment gradually with planned tapering of schedule.
- Store tablets at 15°–30° C (59°–86° F) in tightly closed container; protect from light.
Adverse Effects (≥1%)
CNS: Confusion, amnesia, mental depression, drowsiness, dizziness, sedation, headache, asthenia, fatigue, insomnia. CV: Bradycardia, palpitation, substernal pain. Special Senses: Rhinitis, tinnitus, taste change; vision disturbances, conjunctivitis, iritis. GI: Dry mouth, constipation, abdominal pain, diarrhea, dysphagia, nausea. Urogenital: Impotence, testicular disorder, urinary incontinence. Musculoskeletal: Leg cramps, hypokinesia. Skin: Dermatitis, pruritus, purpura, sweating. Other: Dyspnea.Interactions
Drug: Alcohol and other cns depressants compound sedation and CNS depression.Pharmacokinetics
Absorption: Readily absorbed from GI tract. Onset: 2 h. Peak: 6 h. Duration: Up to 24 h. Distribution: Crosses placenta. Metabolism: In liver. Elimination: 80% in the urine in 24 h. Half-Life: 17 h.Nursing Implications
Assessment & Drug Effects
- Do not discontinue abruptly; may cause plasma and urinary catecholamine increases leading symptoms of tachycardia, insomnia, anxiety, nervousness. Rebound hypertension (i.e., increases in BP to levels significantly greater than those before therapy) may occur 2–7 d after abrupt drug withdrawal, but serious effects rarely develop.
- Monitor BP until it is stabilized. Report a rise in pressure that occurs toward end of dose interval; a divided dose schedule may be ordered.
- Assess mental status and alertness. Adverse effects tend to be dose-dependent, increasing significantly with doses above 3 mg/d.
Patient & Family Education
- Continue drug even after you feel well. This is a maintenance dosage regimen (dose and dose intervals). If 2 or more doses are missed, consult physician about how to reestablish dosage regimen.
- Employ measures to keep mouth moist; saliva substitutes (e.g., Moi-Stir, Xero-Lube) are available OTC. If dry mouth persists >2 wk, patient should check with dentist.
- Do not drive or engage in other potentially hazardous tasks requiring alertness until response to drug is known.
- Avoid alcohol and do not self-medicate with OTC drugs such as sleeping medications, or cough medications without consulting physician.
Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; 
Canadian drug name; 
Prototype drug