Clonidines

Clonidine is a medication that acts as an alpha-2 adrenergic agonist. It is available in oral tablet forms and as a transdermal patch, and it has been marketed under brand names including Catapres and Dixarit. The drug reduces sympathetic outflow from the brain, lowering peripheral vascular resistance and heart rate.

It is used to treat hypertension, including certain cases of resistant hypertension, and as part of perioperative sedation. It is commonly used off-label as a non-stimulant treatment for attention-deficit/hyperactivity disorder in children and adolescents. It can also alleviate withdrawal symptoms from opioids, alcohol, and nicotine, and is sometimes used to aid sleep or sedation in medical settings.

Mechanism: clonidine binds to presynaptic alpha-2 adrenergic receptors in the CNS, reducing norepinephrine release and sympathetic tone, which lowers blood pressure. The patch delivers continuous low-dose exposure for several days.

Pharmacokinetics: oral clonidine is well absorbed, with a half-life of about 12 to 16 hours in adults and subject to hepatic metabolism with renal excretion of metabolites. The transdermal patch provides a steady dose over 7 days, with slower onset but sustained effect.

Adverse effects: common include sedation, drowsiness, dizziness, dry mouth, constipation, and orthostatic or symptomatic hypotension. Bradycardia can occur, particularly in older adults or those with heart disease. Abrupt discontinuation may cause rebound hypertension and tachycardia. Caution with other CNS depressants, beta-blockers, or monoamine oxidase inhibitors.