Colidine
Brand name:- Catapres 150ug , Arkamine 100ug tab.
Clonidine is an alpha-2 agonist. It works by relaxing blood vessels which makes the heart more efficient at pumping blood around the body.
Pharmacodynamic:-
Clonidine functions through agonism of alpha-2 adrenoceptors which have effects such as lowering blood pressure, sedation, and hyperpolarization of nerves. It has a long duration of action as it is given twice daily and the therapeutic window is between 0.1mg and 2.4mg daily.
Pharmacokinetics:-
Colidine is well absorbed orally; peak occurs in 2-4 hours; ½ to⅔ of an oral dose is excreted unchanged in urine, the rest as metabolites. Plasma t½ is 8-12 hours . Effects of a single dose lasts for 6-24 hours .
Mechanism of action:-
Clonidine is primarily an alpha-2 adrenoceptor agonist which causes central hypotensive and anti -arrhythmogenic effects. The alpha-2 adrenoceptor is coupled to the G-proteins Go and Gi. Gi inhibits adenylyl cyclase and activates opening of a potassium channel that causes hyperpolarization.Clonidine binding to the alpha-2 adrenoceptor causes structural changes in the alpha subunit of the G-protein, reducing its affinity for GDP.Magnesium catalyzes the replacement of GDP with GTP. The alpha subunit dissociates from the other subunits and associates with an effector.
The stimulation of alpha-2 adrenoceptors in the locus coeruleus may be responsible for the hypnotic effects of clonidine as this region of the brain helps regulate wakefulness. Clonidine can also decrease transmission of pain signals at the spine.Finally clonidine can affect regulators of blood pressure in the ventromedial and rostral-ventrolateral areas of the medulla.
Used:-
Clonidine is used in the treatment of Hypertension (high blood pressure). It can also be used to prevent migraine attacks and hot flushes that may occur in women during the menopause.
Side effects:-
Dizziness, Dryness in mouth, Headache, Nausea, Fatigue, Orthostatic hypotension (sudden lowering of blood pressure on standing), Erectile dysfunction, Enlarged salivary gland.
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