Active Ingredients

Clonidine – Effect, Application & Risks


Clonidine is a sympathomimetic from the group of imidazolines. It is mainly used to treat arterial hypertension ( high blood pressure ). Due to severe side effects , it is considered a reserve therapeutic agent.

What is clonidine?

The drug clonidine is a sympathomimetic that belongs to the group of imidazolines. It can be used to treat hypertension, help with drug withdrawal, as part of the so-called clonidine inhibition test, in hypertensive crisis , against chronic open-angle glaucoma and for sedation.

It can also be used to a limited extent for sedation and analgesia . Due to relatively strong side effects, however, it is only used as a reserve therapeutic agent in the treatment of hypertension and drug withdrawal.

Pharmacological action

With clonidine, several mechanisms of action can be distinguished through which the substance acts. On the one hand, the activation of presynaptic α2-adrenoceptors, furthermore the activation of postsynaptic α2-adrenoceptors, as well as the inhibition of adrenaline release in the adrenal medulla .

Clonidine binds to presynaptic α2-adrenoceptors in the central nervous system as well as in the periphery. This binding leads to a reduced release of norepinephrine via the G protein-coupled signaling cascade . This reduced release of norepinephrine leads to a reduction in sympathetic tone .

Furthermore, clonidine also activates the postsynaptic α2-adrenoceptors. This occurs particularly in the area of ​​the nucleus tractus solitarii , the switching point of the baroreceptor reflex ( reaction to changes in blood pressure triggered by the baroreceptors ). The already mentioned inhibition of adrenaline release in the adrenal medulla, together with the stimulation of central imidazoline receptors, leads to a further increase in the sympatholytic effect.

Clonidine has an effect even in very small doses of a few micrograms. The plasma half-life is about nine to eleven hours, the LD50 dose when administered orally to mice is 108 mg·kg^-1. It is partially metabolized in the liver , but 65% of the active substance is excreted unchanged via the kidneys .

Clonidine can be administered either orally in the form of a tablet or intravenously. Clonidine crosses the blood-brain barrier and is excreted in breast milk . The bioavailability is about 75%. The volume of distribution is 2 l kg^−1.

Medical Application & Use

Clonidine can be used to treat the following conditions: arterial hypertension; therapy-refractory gestational hypertension ; Hypertensive crisis; chronic open-angle glaucoma; migraine ; opioid withdrawal syndrome; Alcohol Withdrawal Syndrome and Postoperative Shivering.

Due to high side effects, clonidine is mainly used as a reserve therapy in combination therapy for the treatment of arterial hypertension and for the supportive treatment of withdrawal syndromes.

Overall, the following effects are present: lowering of blood pressure, reduction of heart rate , lowering of sympathetic tone in withdrawal, sedation (minor) and pain relief.

The main area of ​​application for clonidine – the therapy of arterial hypertension – goes back to a rather accidental discovery in the 1960s. Various substances, including clonidine, were tested for their ability to decongest the nasal mucosa . In the course of these tests, the sharp reduction in heart rate and blood pressure were noticeable. Medicine then used these effects therapeutically. Clonidine thus became primarily a therapeutic agent in arterial hypertension. In animal experiments, sedative and analgesic effects were also later determined.

However, it should be noted that clonidine has relatively strong side effects and for this reason other drugs with fewer side effects should be preferred.

Risks & side effects

The strong side effects already mentioned exist in the form of dry mouth , constipation (constipation), reduced saliva and gastric juice production, fatigue , depressive mood , sedation and erectile dysfunction .

Clonidine should not be used concomitantly with diuretics , hypnotics , vasodilators or alcohol , as these substances lead to an increase in the effect of clonidine. Even when taking neuroleptics , clonidine should not be used. After intravenous administration, an initial increase in blood pressure is possible.

Clondin should not be used if hypersensitivity ( allergy ) to clonidine is known. Other contraindications are sinus node syndrome , bradycardia (heart rate below 50/minute), endogenous depression, certain cardiac arrhythmias , coronary heart disease , acute myocardial infarction , advanced arterial occlusive disease (pAVK), Raynaud’s syndrome , thromboangiitis obliterans , in cerebrovascular insufficiency, in renal insufficiency and in constipation. Also duringClonidine is contraindicated during pregnancy and lactation .

Lisa Newlon
 | Website

Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.