Guanfacine

INTRODUCTION

Indications

Hypertension (with thiazide-type diuretics).

Action

Stimulates CNS alpha₂-adrenergic receptors, producing a decrease in sympathetic outflow to heart, kidneys, and blood vessels. Result is decreased blood pressure and peripheral resistance, a slight decrease in heart rate, and no change in cardiac output. Therapeutic Effects: Lowering of blood pressure.

Adverse Reactions/Side Effects

CNS: drowsiness, weakness, depression, dizziness, fatigue, headache, insomnia. EENT: tinnitus. Resp: dyspnea. CV: bradycardia, chest pain, palpitations, rebound hypertension. GI: constipation, dry mouth, abdominal pain, nausea. GU: erectile dysfunction.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Assess blood pressure (BP) periodically and compare to normal values (See Appendix F). Document whether drug therapy is successful in controlling hypertension.

• Assess heart rate, ECG, and heart sounds, especially during exercise (See Appendices G, H). Report an unusually slow heart rate (bradycardia) or signs of other arrhythmias, including palpitations, chest discomfort, shortness of breath, fainting, and fatigue/weakness.

• Assess dizziness and weakness that might affect gait, balance, and other functional activities (See Appendix C). Report balance problems and functional limitations to the physician, and caution the patient and family/caregivers to guard against falls and trauma.

• Be alert for signs of depression or other changes in mood and behavior. Notify physician if these changes become problematic.

• Be alert for a rapid increase in BP if guanfacine is suddenly discontinued (rebound hypertension). Report this increase to the physician immediately.

Interventions

• Because of the risk of arrhythmias and abnormal BP responses, use caution during aerobic exercise and other forms of therapeutic exercise. Assess exercise tolerance frequently (BP, heart rate, fatigue levels), and terminate exercise immediately if any untoward responses occur (See Appendix L).

• Avoid physical therapy interventions that cause systemic vasodilation (large whirlpool, Hubbard tank). Additive effects of this drug and the intervention may cause a dangerous fall in BP.

• To minimize orthostatic hypotension, advise patient to move slowly when assuming a more upright position.

Patient/Client-Related Instruction

• Remind patients to take medication as directed to control hypertension even if they are asymptomatic.

• Counsel patients about additional interventions to help control BP, such as regular exercise, weight loss, sodium restriction, stress reduction, moderation of alcohol consumption, and smoking cessation.

• Instruct patient or family/caregivers to report other bothersome side effects such as severe or prolonged headache, fatigue, drowsiness, sleep loss, ringing/buzzing in the ears (tinnitus), difficult/labored breathing, sexual dysfunction, skin reactions (rash, excessive sweating), or GI problems (constipation, nausea, abdominal pain, dry mouth).

Pharmacokinetics

Absorption: Well absorbed (80%) following oral administration.

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