clonidine hydrochloride
Catapres, Catapres-TTS, Dixarit ◆

Available forms
Available by prescription only
Tablets: 0.1 mg, 0.2 mg, 0.3 mg
Transdermal: TTS-1 (releases 0.1 mg/24 hours); TTS-2 (releases 0.2 mg/24 hours); TTS-3 (releases 0.3 mg/24 hours)

Indications and dosages
 Hypertension. Adults: Initially, 0.1 mg P.O. b.i.d.; then increased by 0.1 per day at weekly intervals until desired response is achieved. Usual dose range is 0.2 to 0.6 mg daily in divided doses. Maximum effective dose is 2.4 mg daily. If transdermal patch is used, apply to area of hairless intact skin once q 7 days.
 Adjunctive therapy in nicotine withdrawal ◇. Adults: Initially, 0.15 mg P.O. daily, gradually increased to 0.4 mg P.O. daily as tolerated. Or, apply transdermal patch (0.2 mg/24 hours) and replace weekly for the first 2 or 3 weeks after smoking cessation.
 Prophylaxis for vascular headache ◇. Adults: 0.025 mg P.O. b.i.d. to q.i.d. up to 0.15 mg P.O. daily in divided doses.
 Treatment of vasomotor menopausal symptoms ◇. Adults: 0.025 to 0.02 mg P.O. b.i.d. Or, 0.1-mg/24 hours patch q 7 days.
 Adjunctive therapy in opiate withdrawal ◇. Adults: 5 to 17 mcg/kg P.O. daily in divided doses for up to 10 days. Adjust dosage to avoid hypotension and excessive sedation, and slowly withdraw drug.
 Ulcerative colitis ◇. Adults: 0.3 mg P.O. t.i.d.
 Neuralgia ◇. Adults: 0.2 mg P.O. daily.
 Tourette syndrome ◇. Adults: 0.15 to 0.2 mg P.O. daily.
 Diabetic diarrhea ◇. Adults: 0.1 to 0.6 mg P.O. q 12 hours or one to two patches weekly (0.3 mg/ 24 hours).
 Growth delay in children ◇. Children: 0.0375 to 0.15 mg/m² P.O. daily.
 To diagnose pheochromocytoma ◇. Adults: 0.3 mg given once.

Pharmacodynamics
Antihypertensive action: Clonidine decreases peripheral vascular resistance by stimulating central alpha-adrenergic receptors, thus decreasing cerebral sympathetic outflow; drug also may inhibit renin release. Initially, clonidine may stimulate peripheral alpha-adrenergic receptors, producing transient vasoconstriction.

Pharmacokinetics
Absorption: Absorbed well from the GI tract when administered orally; absorbed well percutaneously after transdermal topical administration.
Distribution: Distributed widely throughout the body.
Metabolism: Metabolized in the liver, where nearly 50% is transformed to inactive metabolites.
Excretion: About 65% of a given dose is excreted in urine; 20% is excreted in feces. Half-life of clonidine ranges from 6 to 20 hours in patients with normal renal function. After oral administration, the antihypertensive effect lasts up to 8 hours; after transdermal application, the antihypertensive effect persists for up to 7 days.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug. Transdermal form is contraindicated in patients hypersensitive to any component of the adhesive layer. Use cautiously in patients with severe coronary disease, recent MI, cerebrovascular disease, and impaired hepatic or renal function.

Interactions
Drug-drug. Barbiturates: May increase CNS depressant effects. Avoid use together.
MAO inhibitors, tolazoline, tricyclic antidepressants: May inhibit antihypertensive effect. Avoid use together.
Propranolol, other beta blockers: May have additive effect, producing bradycardia. Avoid use together.
Drug-herb. Capsicum: May reduce antihypertensive effect. Discourage use together.
Drug-lifestyle. Alcohol use: Increases CNS depressant effects. Discourage alcohol use.

Adverse reactions
CNS: drowsiness, dizziness, fatigue, sedation, weakness, malaise, agitation, depression.
CV: orthostatic hypotension, bradycardia, severe rebound hypertension.
GI: constipation, dry mouth, nausea, vomiting, anorexia.
GU: urine retention, impotence.
Metabolic: weight gain.
Skin: pruritus, dermatitis (with transdermal patch), rash.
Other: loss of libido.

Effects on lab test results
None reported.

Overdose and treatment
Signs and symptoms of overdose include bradycardia, CNS depression, respiratory depression, hypothermia, apnea, seizures, lethargy, agitation, irritability, diarrhea, and hypotension; hypertension also has been reported.
 Don’t induce emesis because rapid onset of CNS depression can lead to aspiration. After adequate airway is assured, empty stomach by gastric lavage followed by administration of activated charcoal. If overdose occurs in patients receiving transdermal therapy, remove transdermal patch. Further treatment is usually symptomatic and supportive.

Special considerations
 ALERT Remove transdermal systems when attempting defibrillation or synchronized cardioversion because of electrical conductivity.
• Clonidine may be used to lower blood pressure quickly in some hypertensive emergencies.
• Don’t discontinue abruptly; reduce dosage gradually over 2 to 4 days to prevent severe rebound hypertension.
• Patients with renal impairment may respond to smaller doses of drug.
• Give drug 4 to 6 hours before scheduled surgery.
• Patient may need oral antihypertensive therapy at start of transdermal therapy.
• Clonidine may decrease urinary excretion of vanillylmandelic acid and catecholamines. It may cause a weakly positive Coombs’ test.
• Daily weight must be recorded at start of therapy to monitor for fluid retention.
Breast-feeding patients
• Clonidine appears in breast milk. An alternative to breast-feeding is recommended during treatment.
Pediatric patients
• Efficacy and safety in children haven’t been established; use drug only if potential benefit outweighs risk.
Geriatric patients
• Elderly patients may require lower doses because they may be more sensitive to the hypotensive effects of clonidine. Monitor renal function closely.

Patient education
• Explain disease and rationale for therapy; emphasize importance of follow-up visits in establishing therapeutic regimen.
• Teach patient signs and symptoms of adverse effects and the need to report them; patient also should report excessive weight gain (more than 2.27 kg [5 lb] weekly).
• Warn patient to avoid hazardous activities that require mental alertness until tolerance develops to CNS effects.
• Advise patient to avoid sudden position changes to minimize orthostatic hypotension.
• Inform patient that ice chips, hard candy, or gum will relieve dry mouth.
• Warn patient to call for specific instructions before taking OTC cold preparations.
• Advise taking last dose at bedtime to ensure night-time blood pressure control.
• Tell patient not to discontinue drug suddenly; rebound hypertension may develop.
• Teach patient to rotate transdermal patch site weekly.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use