Clonidine
A central alpha-2 agonist used for high blood pressure, ADHD, opioid withdrawal, menopausal hot flashes and migraine prevention.
Drug card
- How it works
- Stimulating alpha-2 receptors in the brainstem to cut sympathetic outflow
- Used for
- High blood pressure
- ADHD, alone or added to a stimulant
- Opioid withdrawal symptoms
- Menopausal hot flashes
- Known for
- Dry mouth
- Drowsiness, sedation and tiredness
- Rebound hypertension if stopped suddenly
- Its name
- -onidine means a central alpha-2 agonist (clonidine type)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does clonidine work?
An imidazoline that acts directly, needing no conversion, on brainstem alpha-2 receptors; it also binds imidazoline I1 receptors, which may add to its effect on blood pressure. Plasma renin activity and catecholamine output fall. How it eases ADHD is not known, and it is not a stimulant.
Like other central alpha-2 agonists: They stimulate alpha-2 adrenergic receptors in the brainstem, which act as a brake on sympathetic nerve traffic. Less norepinephrine is released, so peripheral resistance, heart rate and blood pressure fall. Clonidine acts directly and also binds imidazoline I1 receptors; methyldopa is a prodrug whose metabolite, alpha-methylnorepinephrine, probably acts in the same way.
Uses
What is clonidine used for?
- High blood pressure
- ADHD, alone or added to a stimulant
- Opioid withdrawal symptoms
- Menopausal hot flashes
- Migraine prevention
- Severe cancer pain, by epidural infusion with opioids
Side effects
Side effects of clonidine
- Dry mouthKnown for
- Drowsiness, sedation and tirednessKnown for
- Rebound hypertension if stopped suddenlyKnown forSerious
- Dizziness or fainting on standing
- Constipation
- Slow heart rate, sometimes severeSerious
- Heart block (AV block)Serious
- Depression and nightmares
- Erectile dysfunction and low libido
- Dry eyes and blurred vision
- Hallucinations and confusion
- Colonic pseudo-obstruction (rare)Serious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Taper over 2 to 4 days rather than stopping; if a beta blocker is also taken, withdraw that several days first.
- With digoxin, verapamil, diltiazem or a beta blocker it can cause severe bradycardia or AV block.
- Sedation adds up with alcohol and other CNS depressants; tricyclic antidepressants can weaken its effect.
- Avoid with sick sinus syndrome or second- or third-degree AV block; severe kidney disease prolongs its half-life.
Good to know: Unlike methyldopa it needs no conversion to work. It comes as tablets, a skin patch and an epidural infusion for cancer pain, and even small amounts swallowed by a child can be toxic.
Remember it
A way to remember it
Alpha-2 is the brake: press it to slow down, but never let go suddenly.
Brainstem alpha-2 receptors work as a brake on sympathetic outflow. Clonidine and methyldopa's metabolite press it, so heart rate and blood pressure fall and people feel drowsy. Stop clonidine abruptly and the brake comes off: catecholamines surge and blood pressure rebounds, which is why it is always tapered.
Written for biofideX
Its name
-onidine means central alpha-2 agonist (clonidine type)
Clonidine stimulates central alpha-2 receptors and cuts sympathetic outflow; moxonidine and brimonidine share the stem. WHO writes it -(o)nidine, part of -nidine.
- Every drug name stem
Its class
Central alpha-2 agonists
Other central alpha-2 agonists with a card:
Easily mixed up with alpha-1 blockers, noradrenergic and specific serotonergic antidepressants and beta blockers.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Clonidine hydrochloride tablets: label (DailyMed)
- Clonidine hydrochloride extended-release tablets: label (DailyMed)
- Clonidine hydrochloride injection for epidural use: label (DailyMed)
- Clonidine 25 microgram tablets: SmPC (emc)
- Clonidine (NCI Thesaurus)
- Clonidine (NHS)
- Common questions about clonidine (NHS)
- Guidelines for the psychosocially assisted pharmacological treatment of opioid dependence (WHO)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Blood pressure
Clonidine is one of 27 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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