Clonidine

Action

Stimulates alpha-adrenergic receptors in CNS, decreasing sympathetic outflow, inhibiting vasoconstriction, and ultimately reducing blood pressure. Also prevents transmission of pain impulses by inhibiting pain pathway signals in brain.

Availability

Solution for epidural injection: 100 mcg/ml in 10-ml vials, 500 mcg/ml in 10-ml vials

Tablets: 100 mcg (0.1 mg), 200 mcg (0.2 mg), 300 mcg (0.3 mg)

Transdermal systems: 2.5 mg total released as 0.1 mg/24 hours (TTS 1), 5 mg total released as 0.2 mg/24 hours (TTS 2), 7.5 mg total released as 0.3 mg/24 hours (TTS 3)

Indications and dosages

➣ Mild to moderate hypertension

Adults: 0.1 mg P.O. b.i.d. (morning and bedtime) alone or with other anti-hypertensives; increase in increments of 0.1 mg/day q week until desired response occurs. Or, one transdermal system applied once q 7 days to hairless area of intact skin on upper outer arm or chest.

➣ Severe pain in cancer patients unresponsive to opioids alone

Adults: Initially, 30 mcg/hour by continuous epidural infusion, titrated upward or downward depending on patient response

Dosage adjustment

• Renal impairment

Off-label uses

• Acute alcohol withdrawal

• Akathisia

• Diarrhea

• Prolonged surgical anesthesia

Contraindications

• Hypersensitivity to drug

• Hypersensitivity to components of adhesive layer (transdermal form)

• Infection at epidural injection site, bleeding problems (epidural use)

• Concurrent anticoagulant therapy

Precautions

Use cautiously in:

• renal insufficiency, serious cardiac or cerebrovascular disease

• elderly patients

• pregnant or breastfeeding patients.

Administration

• For epidural use, dilute drug solution in normal saline solution, as ordered.

• To minimize sedative effects, give largest portion of maintenance P.O. dose at bedtime.

Adverse reactions

CNS: drowsiness, depression, dizziness, nervousness, nightmares

CV: hypotension (especially with epidural use), palpitations, bradycardia

GI: nausea, vomiting, constipation, dry mouth

GU: urinary retention, nocturia, erectile dysfunction

Metabolic: sodium retention

Skin: rash, sweating, pruritus, dermatitis

Other: weight gain, withdrawal phenomenon

Interactions

Drug-drug. Amphetamines, beta-adrenergic blockers, MAO inhibitors, prazosin, tricyclic antidepressants: decreased antihypertensive effect Beta-adrenergic blockers: increased withdrawal phenomenon

CNS depressants (including antihistamines, opioids, sedative-hypnotics): additive sedation

Epidurally administered local anesthetics: prolonged clonidine effects

Levodopa: decreased levodopa efficacy

Myocardial depressants (including beta-adrenergic blockers): additive bradycardia

Other antihypertensives, nitrates: additive hypotension

Verapamil: increased risk of adverse cardiovascular reactions

Drug-herbs. Capsicum: reduced anti-hypertensive effect

Drug-behaviors. Alcohol use: increased sedation

Patient monitoring

• Monitor patient for signs and symptoms of adverse cardiovascular reactions.

• Frequently assess vital signs, especially blood pressure and pulse.

• Monitor patient for drug tolerance and efficacy.

Patient teaching

• Instruct patient to move slowly when sitting up or standing, to avoid dizziness or light-headedness caused by sudden blood pressure decrease.

☞ Caution patient not to stop taking drug abruptly.

• As appropriate, review all other significant adverse reactions and interactions, especially those related to the drugs, herbs, and behaviors mentioned above.