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Sunday, July 27, 2025

Clonidine


Clonidine is a centrally acting antihypertensive agent with alpha-2 adrenergic agonist properties. It is used in various clinical contexts beyond hypertension, including attention-deficit/hyperactivity disorder (ADHD), opioid withdrawal, menopausal flushing, neuropathic pain, and sleep disorders. Because of its ability to suppress sympathetic outflow from the central nervous system (CNS), it produces a range of therapeutic effects involving cardiovascular, neurologic, and autonomic systems.

This comprehensive profile explores its pharmacology, therapeutic indications, dose regimens, adverse effects, contraindications, precautions, and potential drug interactions.

Drug Classification

  • Pharmacologic class: Centrally acting alpha-2 adrenergic receptor agonist

  • Therapeutic class: Antihypertensive, sedative, anxiolytic, ADHD agent, opioid withdrawal aid

  • Drug schedule: Prescription-only; not controlled

Brand Names

  • Catapres® – Immediate-release tablets

  • Kapvay® – Extended-release tablets (used for ADHD)

  • Dixarit® (UK, for migraine and menopausal flushing)

  • Duraclon® – Injectable clonidine for epidural use

  • Nexiclon XR® – Once-daily extended-release formulation (US)

Mechanism of Action

Clonidine stimulates alpha-2 adrenergic receptors in the brainstem, particularly in the nucleus tractus solitarius (NTS) and locus coeruleus, resulting in:

  • Inhibition of sympathetic outflow

  • Reduced norepinephrine release

  • Decrease in peripheral vascular resistance, heart rate, and blood pressure

It does not affect renal blood flow significantly and does not cause postural hypotension to the same degree as other antihypertensives.

Therapeutic Uses

1. Hypertension (Primary Indication)

  • Particularly in resistant hypertension

  • Used alone or in combination with other antihypertensives

2. Attention-Deficit/Hyperactivity Disorder (ADHD)

  • As Kapvay® (ER formulation), either monotherapy or adjunct to stimulants (e.g., methylphenidate)

  • Helps with hyperactivity, impulsivity, tics, and sleep disturbances

3. Opioid Withdrawal

  • Alleviates autonomic symptoms: sweating, tachycardia, restlessness

  • Often used in detox programs or as adjunct to buprenorphine

4. Menopausal Flushing

  • Off-label use in women who cannot take hormone replacement therapy

5. Migraine Prophylaxis

  • Especially in children or those unresponsive to beta blockers

6. Anxiety and PTSD

  • Particularly in nightmares, hyperarousal, and startle responses

7. Sedation / Sleep Aid

  • Used off-label in children with ADHD or autism for sleep onset insomnia

8. Epidural Analgesia

  • As Duraclon®, used in combination with opioids in intractable cancer pain

Dosage and Administration

Hypertension (Immediate-Release Tablets)

  • Initial: 0.1 mg twice daily

  • May increase by 0.1 mg/day every 1–2 weeks

  • Usual maintenance: 0.2–0.6 mg/day in 2–3 divided doses

  • Maximum: 2.4 mg/day

ADHD (Kapvay® Extended-Release)

  • Children >6 years:

    • Start: 0.1 mg at bedtime

    • Increase by 0.1 mg/day weekly, divided BID

    • Max: 0.4 mg/day (0.2 mg BID)

Opioid Withdrawal

  • 0.1–0.3 mg every 6–8 hours as needed

  • Monitor for hypotension and bradycardia

Menopausal Symptoms

  • 0.05–0.1 mg twice daily

Migraine Prophylaxis

  • 25 mcg–75 mcg BID (UK dose range)

Epidural Infusion (Duraclon®)

  • 30 mcg/hr (usual rate) via continuous epidural infusion

Taper gradually over 2–7 days to avoid rebound hypertension

Pharmacokinetics

  • Absorption: 100% bioavailable orally

  • Peak plasma levels: 1–3 hours (IR), 5–7 hours (ER)

  • Half-life: 12–16 hours (can be prolonged in renal impairment)

  • Metabolism: Minimal hepatic metabolism

  • Elimination: Primarily renal (40–60% unchanged)

Contraindications

  • Known hypersensitivity to clonidine

  • Severe bradyarrhythmias (e.g., sick sinus syndrome, AV block without pacemaker)

  • Avoid epidural form in anticoagulated patients

Precautions and Warnings

  • Rebound hypertension on abrupt discontinuation

  • May exacerbate depression or cognitive slowing

  • Monitor for bradycardia, orthostatic hypotension, especially in elderly

  • Use caution in renal impairment—dose reduction may be necessary

  • Sedation risk when combined with CNS depressants

  • Risk of QT prolongation (rare)

Adverse Effects

Common

  • Dry mouth

  • Sedation, drowsiness

  • Dizziness, orthostatic hypotension

  • Constipation

  • Fatigue

Less Common

  • Bradycardia

  • Depression

  • Sexual dysfunction

  • Fluid retention

  • Nightmares or vivid dreams

  • Skin reactions (patch form)

Rebound Effects

  • Abrupt withdrawal can lead to:

    • Severe hypertension

    • Tachycardia

    • Nervousness, agitation

  • Taper over 2–7 days

Drug Interactions

CNS Depressants

  • Alcohol, benzodiazepines, opioids → additive sedation, hypotension

Antihypertensives

  • Beta blockers: Avoid abrupt discontinuation of either, due to risk of rebound hypertension or bradycardia

  • Diuretics: May enhance hypotensive effects

Tricyclic Antidepressants

  • May reduce clonidine’s antihypertensive efficacy

MAO Inhibitors

  • Use with caution due to blood pressure variability

Heart Rate Modulators

  • Digoxin, verapamil, diltiazem → risk of bradycardia, AV block

Pregnancy and Lactation

Pregnancy

  • Category C (US): Crosses placenta

  • Use only if benefits outweigh risks; may be used in pregnancy-induced hypertension as second-line

Lactation

  • Excreted in breast milk

  • Use with caution, especially in preterm or low birth weight infants

Special Populations

Renal Impairment

  • Dose adjustment may be needed due to renal excretion

Elderly

  • Increased sensitivity to hypotension and sedation

  • Start at lower doses

Pediatrics

  • Extended-release formulation (Kapvay) licensed for ADHD in children ≥6 years

Withdrawal Considerations

  • Rebound hypertension can be life-threatening

  • Taper over several days

  • Consider temporary beta-blocker coverage (e.g., atenolol) if stopping clonidine in hypertensive patients

Patient Counseling Points

  • Take at the same times daily, with or without food

  • Do not stop suddenly

  • Rise slowly from sitting or lying down to reduce dizziness

  • Avoid alcohol and sedatives unless approved

  • Expect dry mouth, constipation, drowsiness

  • Keep adequate hydration

  • In patch form:

    • Apply to hairless, clean area

    • Rotate sites weekly

    • Do not expose to direct heat (e.g., hot tubs) as it increases absorption

Monitoring

  • Blood pressure and heart rate regularly

  • Signs of CNS depression or sedation

  • Renal function if used long-term

  • Behavioral response in ADHD patients

  • ECG if combined with other QT-prolonging agents




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