Synonyms in a broader sense
Catapresan®
Introduction
Clonidine is a drug substance that is mainly used in intensive care medicine. In addition to high blood pressure, especially very high dangerous blood pressure values, clonidine is also used for restlessness. A special feature is its use in the treatment of withdrawal syndromes, for example opioid or alcohol withdrawal.
Clonidine acts on the autonomic nervous system. The autonomic nervous system consists of two parts. The sympathetic nervous system is the invigorating part, which is mainly active during excitement, stress and struggle.
The parasympathetic nervous system, which in many cases has exactly the opposite function and is active during rest, sleep and digestion, for example. The regulation of blood pressure is an essential task of the autonomic nervous system. Normally there is a balance between these two parts.
In special situations, however, there can be shifts in balance. To prevent or suppress an overshooting of the sympathetic part, this system has a brake. Clonidine enhances this brake by activating the same receptors (?2-receptors). As so-called ?2-mimetics (also ?2-agonist) they suppress the release of certain excitatory messenger substances (neurotransmitters or catecholamines such as norepinephrine), which are essential for the regulation of blood pressure. ?2- receptors are thus braking receptors and also involved in the transmission of pain stimuli, which explains the pain-inhibiting effect of clonidine.
Application
Clonidine is of little importance today for the usual high blood pressure therapy because the side effects for the patient are considerable. The main target of clonidine is the nervous system, which is of great importance for symptom relief in withdrawal therapy, including alcohol or opioid withdrawal. Withdrawal is associated with problems caused by a flooding of excitatory messenger substances (catecholamine flooding), which the clonidine reduces by activating the inhibitory receptors, which then reduces the release of the excitatory substances (especially norepinephrine).
Clonidine reaches the nervous system well in this process. In intensive care medicine, clonidine can be used for post-operative sedation and in pain therapy (as a coanalgesic). Its use is also important in cases of a strong rise in blood pressure, which is associated with life-threatening blood pressure values (hypertensive crisis).
The baroreceptor reflex is also important in the regulation of blood pressure. These pressure-sensitive receptors, which are located at specific sites in the arterial vascular system, react more sensitively to changes in blood pressure due to clonidine. This results in a slowed heartbeat with reduced blood ejection volume and dilation of vessels (vasodilation).
As a result, blood pressure drops. It is usually administered as an infusion through the veins (intravenously, i.v.). However, clonidine is also available as an injection which is given under the skin (subcutaneously, see c.).
