Clonidine is a sympathomimetic from the group of imidazolines. It is mainly used to treat arterial hypertension (high blood pressure). Due to strong side effects, it is considered a reserve therapeutic.
What is clonidine?
The drug clonidine is a sympathomimetic that belongs to the group of imidazolines. It can be used to treat hypertension, to support drug withdrawal, in the context of the so-called clonidine inhibition test, for hypertensive crisis, against chronic open-angle glaucoma and for calming.
It can also be used to a limited extent for sedation and analgesia. Due to the relatively strong side effects, however, it is only used as a reserve therapeutic in the treatment of hypertension and drug withdrawal.
Pharmacological effect
In the case of clonidine, several mechanisms of action can be distinguished through which the substance works. On the one hand the activation of presynaptic α2-adrenoreceptors, on the other hand the activation of postsynaptic α2-adrenoreceptors as well as the inhibition of the adrenaline release in the adrenal medulla.
Clonidine binds to presynaptic α2-adrenoreceptors both in the central nervous system and in the periphery. This binding leads to a reduced release of norepinephrine via the G-protein coupled signal cascade. This reduced release of noradrenaline leads to a reduction in sympathetic tone.
Furthermore, clonidine also activates the postsynaptic α2-adrenoreceptors. This happens especially in the area of the nucleus tractus solitarii, the switching point of the baroreceptor reflex (reaction to the change in blood pressure triggered by the baroreceptors). The aforementioned inhibition of the release of adrenaline in the adrenal medulla leads, together with the stimulation of central imidazoline receptors, to a further strengthening of 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 for oral administration to mice is 108 mg kg ^ -1. It is partially metabolized in the liver, but 65% of the active ingredient 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 approx. 75%. The volume of distribution is 2 l kg ^ −1.
Medical application & use
Clonidine can be used to treat the following conditions: arterial hypertension; refractory pregnancy hypertension; Hypertensive crisis; chronic open-angle glaucoma; Migraine; Opioid withdrawal syndrome; Alcohol withdrawal syndrome and postoperative shivering.
Due to the high side effects, clonidine is mainly used as a reserve therapeutic in combination therapy for the treatment of arterial hypertension and for the supportive treatment of withdrawal syndromes.
Overall, the following effects are present: lowering blood pressure, lowering the heart rate, lowering the sympathetic tone in withdrawal, sedation (less pronounced), and pain relief.
The main area of application of clonidine - the therapy of arterial hypertension - goes back to a rather accidental discovery in the 1960s. Various substances, including Clonidine was tested for its ability to make the lining of the nose swell. In the course of these tests, the sharp drop in heart rate and blood pressure were noticed. Medicine then made therapeutic use of these effects. The clonidine thus became mainly a therapeutic agent for arterial hypertension. In animal experiments, sedating and analgesic effects were also found later.
It should be noted, however, that clonidine has relatively strong side effects and for this reason other active ingredients with fewer side effects should be preferred.
Risks & side effects
The strong side effects already mentioned exist in the form of dry mouth, constipation, decreased saliva and gastric juice production, fatigue, depressive mood, sedation and erectile dysfunction.
Clonidine should not be used at the same time as diuretics, hypnotics, vasodilators or alcohol, as these substances increase the effectiveness of clonidine. Even when taking neuroleptics, clonidine should not be used. An initial increase in blood pressure is possible after intravenous administration.
Clondin must not be used if you are known to be hypersensitive (allergic) to clonidine. Further 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 (PAOD), Raynaiterud's syndrome, and thrombo angiitis , cerebrovascular insufficiency, renal insufficiency and constipation (constipation). Clonidine is also contraindicated during pregnancy and breastfeeding.
