Phil Pharmawealth
Full Prescribing Info
Clonidine (as hydrochloride).
Each mL contains: Clonidine (as hydrochloride) 150 mcg.
Pharmacology: Clonidine is an imidazoline antihypertensive that appears to act centrally to reduce sympathetic tone, resulting in a fall in diastolic and systolic blood pressure and a reduction in heart rate. The exact mechanism is unclear, clonidine stimulates α2 adrenoceptors and central imidazoline receptors, but it is not known which receptors mediate which effects. It also acts peripherally, and this peripheral activity may be responsible for the transient increase in blood pressure seen during rapid IV administration as well as contributing to the hypotensive effects during chronic administration. Peripheral resistance is reduced during continuous treatment. Cardiovascular reflexes remain intact so postural hypotension occurs infrequently.
Pharmacokinetics: About 50% of a dose is metabolized in the liver. It is excreted in the urine as unchanged drug and metabolites 40 to 60% of an oral dose being excreted in 24 hours as unchanged drug; about 20% of a dose is excreted in the feces, probably via enterohepatic circulation. The elimination half-life has been various reported between 6 and 24 hours, extended up to 41 hours in patients with renal impairment.
Clonidine is used in the management of hypertension, including hypertensive crises although other drugs with fewer side effects are now generally preferred. It may be given in conjunction with a thiazide diuretic, but combination with a beta-blocker should be avoided where possible. Clonidine has also been used in the prophylactic treatment of migraine or recurrent vascular headaches and in the treatment of menopausal flushing. It is used in conjunction with opioids in the management of cancer pain and has been tried for various other forms of pain. Other uses of clonidine have included the symptomatic treatment of opioid withdrawal, the diagnosis of phaeochromocytoma and administration as eye drops in the management of glaucoma. It has also been tried in Tourette's syndrome and numerous other disorders.
Dosage/Direction for Use
Clonidine hydrochloride may be given by slow intravenous injection over 10 to 15 minutes in hypertensive crises, usually in doses of 150-300 μg. The effect usually appears within 10 minutes, but transient hypertension may precede hypotension if the injection is administered too rapidly. The hypotensive effect reaches a maximum about 30 to 60 minutes after administration and the duration is about 3 to 7 hours; up to 750 μg may be given intravenously over 24 hours. Although oral administration does not produce a sufficiently rapid hypotensive effect for use in an emergency situation, a dose of 100 to 200 μg initially followed by 50 to 100 μg every hour until control of blood pressure is achieved or a maximum of 500 to 800 μg is reached, has been recommended for the control of severe hypertension.
In the prophylaxis of migraine or recurrent vascular headaches and in the treatment of menopausal flushing, a dose of 50 μg twice daily by mouth has been employed, increased if there is a remission after 2 weeks, to 75 μg twice daily.
In the management of severe cancer pain, clonidine hydrochloride may be given by continuous epidural infusion in combination with an opioid, in an initial dose of 30 μg per hour, adjusted according to response.
Special Precautions
Clonidine should be used with caution in patients with cerebrovascular disease, ischaemic heart disease including myocardial infarction renal impairment, occlusive peripheral vascular disorders such as Raynaud’s disease, or these with a history of depression.
Clonidine causes drowsiness and patients should not drive or operate machinery where loss of attention could be dangerous.
Systemic effects also occur following epidural clonidine administration and patients should be loosely monitored, particularly during the first few days of therapy.
Intravenous injections of clonidine should be given slowly especially in patients already receiving other antihypertensives such as guanethidine or reserpine.
Withdrawal of clonidine therapy should be gradual s sudden discontinuation may cause rebound hypertension, sometimes severe. Symptoms of increase catecholamine release such as agitation, sweating tachycardia, headache and nausea may also occur. Betablockers can exacerbate the rebound hypertension and if clonidine is being given concurrently with a beta blocking drug, clonidine should not be discontinued until several days after the withdrawal of the beta blocker. It has been suggested that patients should be warned of the risk of missing a dose or stopping the drug without consulting their doctor and should carry a reserve supply of tablets.
Although hypotension may occur during anesthesia in clonidine-treated patients clonidine should not be withdrawn; indeed, if necessary it should be given intravenously during the operation to avoid the risk of rebound hypotension.
Adverse Reactions
Drowsiness, dry mouth, dizziness and headache commonly occur during the initial stages of therapy with clonidine. Constipation is also common and other adverse effects which have been reported include depression, anxiety, fatigue, nausea, anorexia, parotid pain, sleep disturbances, vivid dreams, impotence and loss of libido, urinary retention or incontinence, slight orthostatic hypotension and dry itching or burning sensations in the eye.
Drug Interactions
The hypotensive effects of clonidine may be enhanced by diuretics, other antihypertensives and other drugs that cause hypotension. However, beta blockers may exacerbate rebound hypertension following clonidine withdrawal and tricyclic antidepressants may antagonize the hypotensive effect. The sedative effect of clonidine may be enhanced by CNS depressants.
Store at temperatures not exceeding 30°C.
MIMS Class
Other Antihypertensives
ATC Classification
C02AC01 - clonidine ; Belongs to the class of imidazoline receptor agonists, centrally-acting antiadrenergic agents. Used in the treatment of hypertension.
Soln for inj (amp) 150 mcg/mL x 1 mL x 10's.
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