Known brand names include Catapres.
A blood pressure pill that acts in the brain to turn down the nerve signals that tighten blood vessels and speed the heart. It treats high blood pressure, and stopping it suddenly can make blood pressure shoot back up.
Clonidine is not a first-line drug for primary hypertension; it is usually an add-on for resistant hypertension, because sedation, dry mouth, and rebound hypertension limit it. Avoid it in patients likely to miss doses. Other clonidine products and off-label uses cover ADHD, opioid and alcohol withdrawal symptoms, and pain, but none of these is part of this tablet label. Do not stop it while a beta blocker continues; withdraw the beta blocker first.
A centrally acting alpha-adrenergic agonist (an imidazoline derivative). It stimulates alpha-adrenoreceptors in the brain stem, cutting sympathetic outflow and lowering heart rate, peripheral and renal vascular resistance, and blood pressure. Renal blood flow and GFR stay essentially unchanged, and postural reflexes are preserved, so orthostatic symptoms are mild and infrequent. Plasma renin, aldosterone excretion, and catecholamine excretion also fall. After an oral dose, pressure falls within 30 to 60 minutes, with the maximum at 2 to 4 hours.
The label does not describe a narrow therapeutic index or direct dosing by measured blood levels of the drug; doses are adjusted to blood pressure response.
Sources: [1]
Doses come from the FDA label. Study tool, not for clinical decisions.
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Patients with renal impairment may benefit from a lower starting dose and need careful monitoring. Half-life rises to as long as 41 hours in severe renal impairment. Routine hemodialysis removes little clonidine, so no supplemental dose is needed after dialysis.
No labeled dose change. About half of an absorbed dose is metabolized in the liver, and much of the rest is excreted unchanged in the urine.
Sources: [1]
None on the current label. Withdrawal with rebound hypertension is a labeled warning instead.
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No specific antidote. Overdose can cause early hypertension, then hypotension, bradycardia, respiratory depression, hypothermia, drowsiness, reduced reflexes, and small pupils, usually within 30 minutes to 2 hours; as little as 0.1 mg has caused toxicity in children. Do not induce vomiting; consider gastric lavage or activated charcoal, and give atropine for bradycardia, IV fluids or vasopressors for hypotension, and vasodilators for hypertension. Naloxone may help respiratory depression, hypotension, or coma, but watch for paradoxical hypertension. Dialysis is unlikely to help much.
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Pregnancy Category C. Clonidine crosses the placenta, and no adequate, well-controlled human studies exist. Rabbit studies showed no teratogenic or embryotoxic effect, while some rat and mouse studies showed more resorptions. Use only if clearly needed.
Clonidine is excreted in human milk, so use caution when giving it to a nursing woman.
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Safety and effectiveness in children have not been established in adequate, well-controlled trials. Children with vomiting illnesses may be especially prone to hypertensive episodes from missed doses. In overdose, as little as 0.1 mg has caused toxicity in children, and CNS depression may be more frequent than in adults.
The label has no separate geriatric section. Older adults may benefit from a lower starting dose.
Sources: [1]