Drug information of Clonidine


Drug group:

Clonidine belongs to a class of drugs (central alpha agonists) that act in the brain to lower blood pressure .Clonidine is used alone or with other medications to treat high blood pressure (hypertension) . Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems.

Mechanism of effect

Clonidine treats high blood pressure by stimulating α2 receptors in the brain, which decreases peripheral vascular resistance, lowering blood pressure. It has specificity towards the presynaptic α2 receptors in the vasomotor center in the brainstem. This binding decreases presynaptic calcium levels, thus inhibiting the release of norepinephrine (NE).
The net effect is a decrease in sympathetic tone. It has also been proposed that the antihypertensive effect of clonidine is due to agonism on the I1 receptor (imidazoline receptor), which mediates the sympatho-inhibitory actions of imidazolines to lower blood pressure.
Its mechanism of action in the treatment of ADHD is to increase noradrenergic tone in the prefrontal cortex (PFC) directly by binding to postsynaptic α2A adrenergic receptors and indirectly by increasing norepinephrine input from the locus coeruleus.


Clonidine stimulates alpha-adrenoreceptors in the brain stem. This action results in reduced sympathetic outflow from the central nervous system and in decreases in peripheral resistance, renal vascular resistance, heart rate, and blood pressure .


Well absorbed following oral administration.
The absolute bioavailability of clonidine on oral administration is 70% to 80%. Peak plasma clonidine levels are attained in approximately 1 to 3 hours.Bioavailability following chronic administration is approximately 65%.
Following intravenous administration, clonidine displays biphasic disposition with a distribution half-life of about 20 minutes and an elimination half-life ranging from 12 to 16 hours. The half-life increases up to 41 hours in patients with severe impairment of renal function. Clonidine crosses the placental barrier.
Protein binding
20-40%, primarily to albumin
About 50% of the absorbed dose is metabolized in the liver. Metabolized via minor pathways. The major metabolite, p-hydroxyclonidine, is present in concentrations less than 10% of those of unchanged clonidine in urine. Four metabolites have been detected, but only p-hydroxyclonidine has been identified.
40-60% is excreted in urine unchanged, 20% is excreted in feces. Less than 10% is excreted by p-hydroxyclonidine.

Drug indications

Analgesic Activity


usual Adult Dose for Hypertension
-Initial dose: 0.1 mg orally 2 times a day (morning and bedtime)
-Titration: Increments of 0.1 mg orally per day may be made at weekly intervals to desired response
-Maintenance dose: 0.2 to 0.6 mg orally per day in divided doses
-Maximum dose: 2.4 mg orally per day in divided doses
Usual Adult Dose for Pain
Epidural infusion:
-Initial dose: 30 mcg/hr as a continuous infusion
-Titration: May be titrated up or down depending on pain relief and occurrence of adverse events
Maximum dose 40 mcg/hr as a continuous infusion
Usual Pediatric Dose for Attention Deficit Disorder
Extended release:
6 years and older:
-Initial dose: 0.1 mg orally at bedtime
-Titration: Increase in 0.1 mg/day increments every 7 days until desired response; doses should be administered twice daily (either split equally or with the higher split dosage given at bedtime)
-Maximum dose: 0.4 mg/day in 2 divided doses

Drug contraindications

heart failure , heart block , Hypotension


- This medicine may cause dryness of the eyes. If you wear contact lenses, this may be a problem for you.
- Clonidine may cause dryness of the mouth. For temporary relief, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute.
- Clonidine will add to the effects of alcohol and other central nervous system (CNS) depressants.
- This medication affects blood pressure, which may cause dizziness and increase your risk of falling.
- This includes low blood pressure, low heart rate, and heart disease. This medication decreases blood pressure and heart rate . You may be at risk for more serious side effects if you already have low blood pressure or a low heart rate.
- Move slowly when sitting up or standing, to avoid dizziness or light-headedness. Dangle your legs briefly before getting out of bed.
- The sympatholytic action of Clonidine may worsen sinus node dysfunction and atrioventricular (AV) block, especially in patients taking other sympatholytic drugs.

Points of recommendation

- Patients should be instructed not to discontinue therapy without consulting their physician. Sudden cessation of Clonidine treatment has, in some cases, resulted in symptoms such as nervousness, agitation, headache, and tremor accompanied or followed by a rapid rise in blood pressure and elevated catecholamine concentrations in the plasma.
- Taking the larger portion of the oral daily dose at bedtime may minimize transient adjustment effects of dry mouth and drowsiness.

Pregnancy level


Related drugs

Ceftizoxime , Guanabenz

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