Clonidine: Effective Central Alpha-2 Agonist Therapy for Hypertension
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Synonyms
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Clonidine hydrochloride is a centrally acting alpha-2 adrenergic agonist, representing a cornerstone in the therapeutic management of hypertension and several off-label conditions. It functions by stimulating alpha-2 receptors in the brainstem, resulting in a reduction of sympathetic outflow from the central nervous system. This leads to a decrease in peripheral vascular resistance, heart rate, and blood pressure, offering a unique mechanism of action distinct from other first-line antihypertensives. Its utility extends beyond hypertension to include the management of attention deficit hyperactivity disorder (ADHD), opioid withdrawal symptoms, menopausal flushing, and certain pain conditions, making it a versatile agent in the clinical arsenal.
Features
- Active Pharmaceutical Ingredient: Clonidine Hydrochloride
- Drug Class: Centrally Acting Alpha-2 Adrenergic Agonist
- Available Formulations: Oral tablets (immediate and extended-release), transdermal patches
- Mechanism of Action: Stimulates pre-synaptic alpha-2 adrenoceptors in the brainstem, reducing sympathetic nervous system outflow
- Bioavailability: Approximately 75-95% for oral tablets; slow, continuous delivery via transdermal system
- Protein Binding: 20-40%
- Metabolism: Hepatic (approximately 50% of absorbed dose)
- Elimination Half-life: 12-16 hours (range 6-23 hours) for oral administration; 7-day delivery system for patches
- Excretion: Primarily renal (40-60% as unchanged drug)
Benefits
- Provides effective blood pressure control through a central mechanism, often used in combination therapy.
- Mitigates the neurovegetative symptoms of opioid withdrawal, such as anxiety, agitation, and sweating.
- Can reduce the frequency and severity of menopausal hot flashes where hormone therapy is contraindicated.
- Used as an adjunctive therapy for ADHD, particularly in cases with co-morbid tic disorders or sleep problems.
- Offers a non-opioid option for managing certain neuropathic and cancer-related pain syndromes.
- The transdermal patch formulation provides steady-state drug delivery, improving adherence and minimizing peak-to-trough fluctuations.
Common use
Clonidine is primarily indicated for the treatment of hypertension, either as monotherapy or, more commonly, as part of a combination regimen with a diuretic or other antihypertensive agents. Its use is well-established in resistant hypertension. Beyond this primary indication, it is frequently employed off-label. In psychiatry, it is used to manage symptoms of ADHD, Tourette syndrome, and anxiety. In addiction medicine, it is a key component of protocols for the detoxification from opioids and alcohol, helping to manage autonomic hyperactivity. It is also utilized in pain management clinics for conditions like diabetic neuropathy, migraine prophylaxis, and cancer pain. Furthermore, it is prescribed for the treatment of menopausal flushing, particularly in patients for whom estrogen therapy is not suitable.
Dosage and direction
Dosage must be individualized based on therapeutic response and tolerability.
Hypertension (Oral tablets):
- Initial dose: 0.1 mg orally twice daily.
- Maintenance dose: May be increased by 0.1 mg to 0.2 mg per day at weekly intervals. The therapeutic dosage range is typically 0.2 mg to 0.6 mg per day in divided doses. Doses exceeding 2.4 mg per day are not recommended.
- Extended-Release tablets: Dosed once daily. The recommended starting dose is 0.17 mg once daily.
Transdermal Patch:
- The patch is applied to a hairless, intact area of skin on the upper arm or torso.
- The initial system is usually the 0.1 mg/24 hr patch, replaced once every 7 days.
- Dosage may be increased after 1-2 weeks by using a larger patch or a combination of patches.
- The site of application should be rotated.
ADHD (Off-label):
- Immediate-Release: Dosing typically starts at 0.05 mg at bedtime, with gradual titration. The total daily dose usually ranges from 0.1 mg to 0.3 mg, given in divided doses (e.g., 3-4 times daily).
- Extended-Release (Kapvay®): Approved for ADHD. Initial dose is 0.1 mg at bedtime, titrated in increments of 0.1 mg per week. The recommended dose range is 0.2 mg to 0.4 mg daily, given either once at bedtime or in divided doses.
Opioid Withdrawal (Off-label):
- A typical regimen involves 0.1 mg to 0.3 mg orally every 4-6 hours, based on the severity of withdrawal symptoms, with a maximum daily dose often around 1.2 mg. The dose is then tapered over 5-7 days.
Administration Note: Abrupt discontinuation of clonidine, especially at higher doses, can cause a rapid rise in blood pressure and elevated catecholamine levels. Therapy should be tapered gradually over 2 to 4 days to avoid rebound hypertension.
Precautions
Patients should be closely monitored, especially at initiation of therapy and during dosage adjustments. Blood pressure and pulse should be measured routinely. Caution is advised in patients with severe coronary insufficiency, recent myocardial infarction, cerebrovascular disease, or chronic renal failure, as the drug can cause bradycardia and hypotension. The transdermal patch can cause skin sensitization (redness, itching); rotating application sites is necessary. Patients should be advised that clonidine may cause drowsiness or sedation, which can impair mental and physical abilities required for tasks such as driving or operating machinery. This sedative effect is often most pronounced during the initial phase of therapy. Alcohol and other CNS depressants may potentiate this effect.
Contraindications
Clonidine therapy is contraindicated in patients with a known hypersensitivity to clonidine hydrochloride or any component of the formulation. The transdermal system is additionally contraindicated in patients with a history of hypersensitivity to any component of the adhesive layer of the patch.
Possible side effect
The most common adverse reactions are dry mouth (approximately 40% of patients), drowsiness (approximately 33%), and sedation. Dizziness is also frequently reported. Other common side effects include:
- Constipation
- Fatigue
- Headache
- Orthostatic hypotension
- Sexual dysfunction Less common but more serious side effects can include:
- Severe bradycardia
- Atrioventricular (AV) block
- Sinus node dysfunction
- Vivid dreams or nightmares
- Depression
- Rebound hypertension upon abrupt withdrawal
- Localized skin reactions (erythema, pruritus) with the transdermal patch
Drug interaction
Clonidine has the potential for significant interactions:
- Tricyclic Antidepressants (e.g., amitriptyline, imipramine): May inhibit the antihypertensive effect of clonidine.
- Beta-Blockers (e.g., propranolol): Concomitant use can potentiate bradycardia. Abrupt clonidine withdrawal during beta-blocker therapy is particularly dangerous, as it can lead to severe rebound hypertension. Beta-blockers should be discontinued several days before slowly tapering clonidine.
- Calcium Channel Blockers (e.g., verapamil, diltiazem): May increase the risk of AV block or severe bradycardia.
- CNS Depressants (e.g., alcohol, benzodiazepines, opioids, barbiturates): Additive sedative effects.
- Levodopa: Possible reduced efficacy of levodopa.
- Other Antihypertensives: Additive hypotensive effects.
Missed dose
If a dose is missed, it should be taken as soon as possible. However, if it is almost time for the next scheduled dose, the missed dose should be skipped. The regular dosing schedule should be resumed. Patients should never take a double dose to make up for a missed one.
Overdose
Manifestations of clonidine overdose include early hypertension (which may be transient), followed by hypotension, bradycardia, respiratory depression, hypothermia, drowsiness, diminished or absent reflexes, and vomiting. Apnea, seizures, and transient cardiac conduction defects may occur. Lethargy can progress to coma. Management is supportive and symptomatic. Atropine may be used for bradycardia. IV fluids and vasopressors (e.g., dopamine or norepinephrine) may be required to treat hypotension. Tolazoline, an alpha-adrenergic blocking agent, has been used as an antidote but is not commonly available. Dialysis is not likely to be effective due to clonidine’s extensive distribution.
Storage
Store at controlled room temperature, 20°C to 25°C (68°F to 77°F). Tablets should be kept in their original container, tightly closed, and protected from light and moisture. Transdermal patches should be kept in their sealed pouches until immediately before use. Keep all medications out of the reach of children and pets.
Disclaimer
This information is for educational and informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned.
Reviews
“Clonidine has been an invaluable tool in our clinic for managing complex hypertension cases, particularly when a central mechanism of action is desired. Its utility in mitigating autonomic hyperactivity during opioid withdrawal is unparalleled.” – Clinical Pharmacologist
“As a child and adolescent psychiatrist, the extended-release formulation has provided a valuable non-stimulant option for treating ADHD, especially in patients with co-morbid tics or significant sleep-onset problems. The sedative effect can be beneficial at night.” – Board-Certified Psychiatrist
“The transdermal delivery system is a game-changer for adherence in our elderly population with hypertension. The once-weekly application simplifies regimens significantly, though dermatological reactions require careful monitoring.” – Geriatrician