Midodrine

INTRODUCTION

Indications

Symptomatic management of refractory orthostatic hypotension in patients whose lives are impaired.

Unlabeled Use: Urinary incontinence.

Action

Activation of alpha₁-adrenergic receptors in arteries and veins. Therapeutic Effects: ↑ in vascular tone and blood pressure.

Adverse Reactions/Side Effects

CNS: anxiety, confusion, head pressure/fullness, headache, nervousness. CV: supine hypertension, bradycardia. GU: urinary urge/retention/frequency, dysuria. Derm: facial flushing, piloerection, pruritus, rash. Neuro: paresthesia. Misc: chills, pain.

PHYSICAL THERAPY IMPLICATIONS

Examination and Evaluation

• Assess blood pressure (BP) when the patient assumes a more upright position (lying to standing, sitting to standing, lying to sitting). Document whether drug therapy is successful in reducing the incidence and severity of orthostatic hypotension; that is, reduced episodes where systolic BP falls >20 mm Hg, or diastolic BP falls >10 mm Hg.

• Assess BP when patient is lying down. Compare to normal values (See Appendix F), and report a sustained increase in BP (hypertension) to the physician.

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

• Monitor and report signs of CNS toxicity, including nervousness, anxiety, confusion, or feelings of pressure or fullness in the head. Sustained or severe CNS signs may indicate overdose or excessive use of this drug.

• Assess signs of paresthesia, including numbness, tingling, and muscle weakness. Perform objective tests, including electroneuromyography and sensory testing to document any drug-related neuropathic changes.

• If used to treat urinary incontinence, monitor the frequency of incontinent episodes to help determine if drug therapy is successful in reducing these episodes.

Interventions

• Because of the risk of cardiovascular stimulation, use caution during aerobic exercise and endurance conditioning. Assess exercise tolerance frequently (BP, heart rate, fatigue levels), and terminate exercise immediately if any untoward responses occur (See Appendix L).

Patient/Client-Related Instruction

• Instruct patient and family/caregivers to report other troublesome side effects such as severe or prolonged headache, chills, pain, skin reactions (rash, itching flushing, goose bumps), or urinary problems (urgency, increased frequency, urinary retention, difficulty initiating urination).

Pharmacokinetics

Absorption: 93% absorbed following oral administration; rapidly converted to desglymidodrine, the active metabolite.

Distribution: Desglymidodrine crosses the blood-brain barrier poorly.

Metabolism and Excretion: Desglymidodrine is 80% excreted by the kidneys.

Half-life: Midodrine—25 min; desglymidodrine—3–4 hr.