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Drug Reference

clonidine

alpha-2 adrenergic agonist· Brands: Catapres, Dixarit, KapvayPOTOP

Mechanism of action
Clonidine is a centrally acting alpha-2 adrenergic agonist. It stimulates alpha-2 receptors in the brainstem, reducing sympathetic outflow from the central nervous system. This leads to decreased peripheral vascular resistance, reduced heart rate and cardiac output, and lower blood pressure. It may also have analgesic and sedative effects through similar central mechanisms.
Pharmacokinetics
Clonidine is well absorbed after oral administration, with peak plasma concentrations at 1 to 3 hours. It is distributed widely, crosses the blood-brain barrier, and is approximately 20% to 40% bound to plasma proteins. Metabolised in the liver, with about 50% of the drug excreted unchanged in the urine. The elimination half-life is 8 to 12 hours, prolonged in renal impairment. Transdermal administration provides steady plasma concentrations over 7 days.
Indications & dosing

Hypertension

Start 0.05 mg twice daily, increase by 0.05-0.1 mg daily at weekly intervals. Dose range 0.2-0.6 mg daily in divided doses.

  • adult · PO: 0.05–0.3 mg BD · Start 0.05 mg twice daily, increase by 0.05-0.1 mg daily at weekly intervals. Dose range 0.2-0.6 mg daily in divided doses.

ADHD (off-label)off-label

Start 0.05 mg at bedtime, titrate by 0.05 mg every 3-7 days. Usually given in divided doses; monitor for sedation.

  • pediatric · PO: 0.05–0.1 mg BD · Start 0.05 mg at bedtime, titrate by 0.05 mg every 3-7 days. Usually given in divided doses; monitor for sedation.

Anxiety (off-label)off-label

Often used as adjunct; start 0.05 mg twice daily, titrate slowly. Sedation is common.

  • adult · PO: 0.05–0.1 mg TDS · Often used as adjunct; start 0.05 mg twice daily, titrate slowly. Sedation is common.

Menopausal flushing (off-label)off-label

Start 0.05 mg twice daily, adjust to response. Max 0.3 mg daily.

  • adult · PO: 0.05–0.15 mg BD · Start 0.05 mg twice daily, adjust to response. Max 0.3 mg daily.

Chronic pain (off-label)off-label

Adjunct for neuropathic pain, start 0.05 mg at night, titrate to 0.1-0.2 mg daily.

  • adult · PO: 0.05–0.1 mg BD · Adjunct for neuropathic pain, start 0.05 mg at night, titrate to 0.1-0.2 mg daily.
Contraindications & precautions
  • Known hypersensitivity to clonidine · Rarely reported, but should be avoided in patients with a history of allergy to clonidine.
  • Severe bradycardia, sick sinus syndrome, or second or third degree heart block · Clonidine can worsen bradycardia and conduction disturbances.
  • Active coronary artery disease · Caution is advised as clonidine may cause hypotension or bradycardia in these patients.
  • Breastfeeding · Clonidine is excreted in breast milk; consider alternative antihypertensives or monitor the infant.
  • Do not discontinue abruptly, reduce dose gradually over 1 to 2 weeks to prevent rebound hypertension.
  • Use with caution in patients with cerebrovascular disease, severe coronary insufficiency, or recent myocardial infarction.
  • Monitor blood pressure and heart rate regularly, especially during initiation and dose adjustment.
  • Caution in patients with renal impairment; dose adjustment may be required.
  • May aggravate sinus node dysfunction or conduction disturbances; use with caution in patients with pre-existing conduction defects.
Adverse effects
  • Dry mouth
  • Drowsiness
  • Dizziness
  • Orthostatic hypotension
  • Constipation
  • Rebound hypertension on abrupt withdrawalserious
  • Severe bradycardiaserious
  • Depressionserious
Renal & hepatic adjustment
  • eGFR 0–30: Reduce initial dose and titrate slowly; monitor for hypotension and bradycardia.
  • Hepatic impairment (severe): No specific dose adjustment; use with caution in severe hepatic impairment.
Monitoring, pregnancy & toxicity
  • Blood pressure · At each dose adjustment and regularly during therapy
  • Heart rate · At each dose adjustment and regularly during therapy
  • Sedation level · Especially when initiating or increasing dose
  • Signs of rebound hypertension · When discontinuing therapy; taper gradually
  • Pregnancy: Clonidine crosses the placenta. Limited data in human pregnancy; used for hypertension and pre-eclampsia. No clear teratogenic risk, but may cause neonatal hypotension or bradycardia. Use only if clearly needed.
  • Toxicity: Bradycardia · Atropine for symptomatic bradycardia; monitor heart rate.
  • Toxicity: Hypotension · IV fluids and supportive measures; monitor blood pressure.
  • Toxicity: Sedation and respiratory depression · Airway and respiratory support; close monitoring.
  • Toxicity: Miosis · Supportive care; not specific treatment required.
Clinical notes
Clonidine is used for hypertension, alone or in combination, and for the treatment of attention deficit hyperactivity disorder (ADHD) in children and adolescents when stimulants are unsuitable. Other uses include menopausal flushing, migraine prophylaxis, and pain management as an adjunct. Adverse effects include dry mouth, drowsiness, dizziness, bradycardia, and rebound hypertension on abrupt withdrawal. It should be tapered gradually. Contraindicated in severe bradycardia or sick sinus syndrome. Caution in renal impairment and depression.

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BNF; local formulary