Clonidine

Indications

• Kapvay extended-release tablets are FDA-approved for ADHD in patients age 6 to 17 years as monotherapy or as adjunct to stimulants.
• Onyda XR, an extended-release oral suspension approved in 2024, is the first liquid nonstimulant for ADHD in patients age 6 and older.
• Immediate-release tablets and the transdermal patch are approved for hypertension in adults and are not approved for ADHD.
• Used off-label for opioid and alcohol withdrawal, where it blunts autonomic hyperactivity, sweating, and restlessness.
• Used off-label for tics and Tourette syndrome, PTSD hyperarousal and nightmares, and sleep-onset insomnia in children with ADHD.
• Epidural clonidine is approved as an adjunct for severe cancer pain, and that formulation carries its own boxed warning against obstetric and perioperative use.

Mechanism of action

• Agonist at presynaptic alpha-2 autoreceptors in the locus coeruleus, reducing central noradrenergic firing and sympathetic outflow.
• Also stimulates postsynaptic alpha-2A receptors in prefrontal cortex, the action shared with guanfacine that improves impulse control.
• It is nonselective across alpha-2A, alpha-2B, and alpha-2C subtypes, which accounts for greater sedation and hypotension than guanfacine.
• Reduced noradrenergic tone explains its benefit in opioid withdrawal, where autonomic symptoms arise from locus coeruleus hyperactivity.
• Partial imidazoline receptor activity contributes to the blood pressure lowering effect and to rebound hypertension on withdrawal.

Pharmacokinetics

• Immediate-release Tmax is 1-3 hours; the extended-release formulations shift peak later and reduce peak sedation.
• Half-life is 12-16 hours in normal renal function and can extend to 41 hours in end-stage renal disease.
• About half the dose is excreted unchanged in urine and the rest is metabolized hepatically, with minor CYP2D6 involvement.
• Bioavailability of oral clonidine is 70-80 percent, and the transdermal patch delivers steady concentrations over 7 days.
• Extended-release and immediate-release forms are not interchangeable on a milligram basis and require separate titration.

Dosing

• Kapvay for ADHD: start 0.1 mg PO at bedtime, increase by 0.1 mg/day weekly to a maximum of 0.4 mg/day, given in two divided doses.
• When divided doses are unequal, give the larger portion at bedtime to concentrate sedation during sleep rather than during school.
• Onyda XR is dosed once daily at bedtime, starting at 0.1 mg and titrating weekly by 0.1 mg to a maximum of 0.4 mg/day.
• Immediate-release clonidine for hypertension in adults: start 0.1 mg PO twice daily, usual range 0.2-0.6 mg/day, maximum 2.4 mg/day.
• Opioid withdrawal off-label: 0.1-0.2 mg PO every 6-8 hours as tolerated, holding for systolic pressure below 90 mmHg.
• Taper by no more than 0.1 mg every 3 to 7 days, since abrupt withdrawal can cause rebound hypertension and severe agitation.

Adverse effects

• Somnolence in 30-40 percent, fatigue, dry mouth, headache, and irritability are the most frequent effects and often limit titration.
• Hypotension, orthostatic dizziness, and bradycardia are dose related and more pronounced than with guanfacine.
• Rebound hypertension, tachycardia, tremor, and agitation follow abrupt discontinuation, especially at higher antihypertensive doses.
• Depressed mood, vivid dreams, and blunted affect are reported and can be mistaken for worsening of the underlying psychiatric disorder.
• Overdose in young children is dangerous, producing bradycardia, hypotension, miosis, and respiratory depression that mimics opioid toxicity.
• Transdermal use adds contact dermatitis, which affects a meaningful minority of patients using the weekly patch.

Monitoring

• Baseline and periodic heart rate and blood pressure, including orthostatic measurements in patients reporting dizziness or falls.
• Ask about daytime sedation and school or work performance, since sedation is the dominant reason clonidine fails in practice.
• Track ADHD or tic severity with a validated scale at baseline and after 4-6 weeks at a stable dose.
• Verify that patients and families understand that missed doses risk rebound hypertension and that stopping requires a taper.
• Reassess renal function in older adults and in patients with chronic kidney disease, since the half-life lengthens substantially.

Interactions

• Additive hypotension and bradycardia with beta-blockers, calcium channel blockers, digoxin, and other antihypertensives.
• Beta-blockers can worsen rebound hypertension during clonidine withdrawal, so stop the beta-blocker first when both are being discontinued.
• Tricyclic antidepressants and mirtazapine antagonize the antihypertensive effect through alpha-2 receptor blockade.
• Additive central nervous system depression with alcohol, benzodiazepines, opioids, and sedating antihistamines.
• Combining with stimulants is common and generally safe, but blood pressure and heart rate should still be tracked at each visit.

Special populations

• Pregnancy: limited human data with no clear teratogenic pattern; it is sometimes continued for hypertension when alternatives are unsuitable.
• Lactation: clonidine is present in human milk and can reduce milk supply, so monitor infant sedation and maternal lactation closely.
• Pediatric: extended-release forms are approved from age 6, and accidental ingestion by toddlers is a recognized poisoning emergency.
• Geriatric: start at the lowest dose because of orthostatic hypotension, falls, sedation, and reduced renal clearance.
• Renal impairment: reduce the dose and extend the interval, since roughly half of the drug is cleared unchanged by the kidney.

Clinical pearls

• Clonidine sedates far more than guanfacine; put the bigger share of the dose at bedtime.
• Never stop it abruptly, and stop any beta-blocker first to avoid rebound hypertension.
• A toddler who swallows one tablet can look opioid-poisoned; treat every ingestion as serious.