guanfacine

guanfacine /guan·fa·cine/ (gwahn´fah-sēn) an α2-adrenergic agonist used in the form of the hydrochloride salt as an antihypertensive.

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guanfacine

Tenex

Pharmacologic class: Centrally acting antiadrenergic

Therapeutic class: Antiadrenergic-sympatholytic, antihypertensive

Pregnancy risk category B

Action

Stimulates central alpha₂-adrenergic receptors, reducing sympathetic nerve impulses from vasomotor center to heart and blood vessels

Availability

Tablets: 1 mg, 2 mg

⊘Indications and dosages

➣ Hypertension

Adults: 1 mg P.O. at bedtime. If response unsatisfactory after 3 to 4 weeks, increase to 2 mg P.O. at bedtime.

Off-label uses

• Attention deficit hyperactivity disorder
• Treatment of heroin withdrawal
• Hypertension in pregnancy

Contraindications

• Hypersensitivity to drug

Precautions

Use cautiously in:
• sedated patients (especially when given with centrally acting depressants)
• pregnant or breastfeeding patients
• children younger than age 12.

Administration

• Give at bedtime to reduce daytime sleepiness.
• Know that therapy shouldn't be stopped abruptly, because this may cause rebound plasma and urinary catecholamines, anxiety, and hypertension.
• Be aware that drug may be used alone or with other agents, especially thiazide diuretics.

Route	Onset	Peak	Duration
P.O.	Unknown	2.6 hr	Unknown

Adverse reactions

CNS: somnolence, insomnia, dizziness, headache, fatigue, amnesia, confusion, depression, hypokinesia, asthenia, malaise, paresthesia, paresis

CV: bradycardia, palpitations, substernal pain

EENT: conjunctivitis, iritis, vision disturbance, tinnitus, rhinitis

GI: nausea, diarrhea, constipation, abdominal pain, dyspepsia, dysphagia, dry mouth

GU: erectile dysfunction, decreased libido

Musculoskeletal: leg cramps

Respiratory: dyspnea

Skin: dermatitis, pruritus, purpura, sweating

Other: taste perversion

Interactions

Drug-drug. CNS depressants: additive sedation

Phenobarbital, phenytoin: decreased elimination half-life and blood level of guanfacine

Drug-behaviors. Alcohol use: additive sedation

Patient monitoring

• Monitor patient for evidence of drug efficacy.
• Monitor patient closely during drug withdrawal.

Patient teaching

• Tell patient to take drug at bedtime to reduce daytime sleepiness.
• Caution patient not to stop taking drug abruptly.
• Advise patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• Tell patient to avoid alcohol during therapy.
• As appropriate, review all other significant adverse reactions and interactions, especially those related to the drugs and behaviors mentioned above.