Guanethidine is a drug used in the therapy of hypertension (high blood pressure) and in local anesthesia to numb certain nerves. The main pharmaceutical producer of guanethidine is the company Alcon, which markets the active ingredient under the name Thilodigon. Thus, guanethidine represents both an antihypertensive and an antisympathotonic agent.
What is guanethidine?
Guanethidine is a medication that is used in the treatment of high blood pressure. In addition, the medical agent guanethidine is able to block nerves, so it can be used for local anesthesia. In addition, guanethidine affects the sympathetic nervous system, making it suitable as an antisympathotonic. The drug guanethidine belongs to the group of active substances known as antihypertensives. Guanethidine is also known by the synonymous terms guanethidine monosulfate, guanethidinum, and guanethidine sulfate. However, drugs containing guanethidine are currently no longer commercially available in many countries, such as Switzerland. Previously, doctors often prescribed the active ingredient guanethidine in the form of tablets with the trade name Ismelin. When used in medications, guanethidine comes in the form of guanethidine monosulfate. This is a crystalline powder of white color. Guanethidine is relatively soluble in water and is one of the derivatives of guanidine. Guanethidine mainly influences the noradrenergic system. Thus, it inhibits the production of the neurological transmitter norepinephrine and reduces the storage capacity of certain neurons for the neurotransmitter.
Pharmacologic effects on the body and organs
The effect of guanethidine is due to the fact that the substance reduces the production of norepinephrine. This is a neurological messenger that plays an important role in the transmission of stimuli. At the same time, ingestion of guanethidine causes neurons to store less norepinephrine. Thus, guanethidine has similarities to the active ingredient reserpine. In addition, the drug guanethidine stabilizes the membranes of the axon and reduces depolarizability. In this way, the drug guanethidine is well suited for use in local anesthesia. In principle, guanethidine has a strong affinity for the systems and processes that transport the neurotransmitter norepinephrine in the nervous system. In medical jargon, these processes are also referred to as norepinephrine pumps. The transport processes take place primarily in the membranes of the salivary vesicles and axons. Thus, guanethidine reduces the removal of extraneuronal catecholamines so that epinephrine and norepinephrine have a longer systemic effect. For this reason, the drug guanethidine is used especially in people with high blood pressure, in whom other therapeutic measures show little or no success. In principle, the ends of the nerve cells release less norepinephrine under the influence of guanethidine, so that a lower proportion of the neurotransmitter is present in the synaptic cleft. Initially, the release of norepinephrine increases as a result of taking guanethidine. However, under the influence of the drug, the responsible structures are unable to reabsorb the noradrenaline produced. This is because the nervous system now stores the substance guanethidine. In the context of local anesthesia, physicians take advantage of the fact that guanethidine reduces the sympathetic conduction of the nerves. However, guanethidine only blocks nerves in the area of the limbs. Patients are first given a tourniquet, and then the doctor injects the guanethidine into the vein. The drug has a duration of action of between one and three days. Helpful here is the fact that guanethidine does not act in the central nervous system.
Medical use and use for treatment and prevention.
The drug guanethidine is mainly used for the treatment of hypertension. In addition, guanethidine is also suitable for local anesthesia, especially in the limbs. In the meantime, however, drugs containing guanethidine have disappeared from the market in numerous countries. Guanethidine is mainly available in the drug Ismelin. The dosage of the tablets depends on the severity of the hypertension as well as the age of the patient. When guanethidine is used in local anesthesia, physicians consider the dose required in each individual case, which can be determined based on the procedure required.
Risks and side effects
Taking guanethidine may cause some side effects that should be weighed by the physician before prescribing it. For example, it increases sensitivity to so-called catecholamines, which include, for example, the neurotransmitter epinephrine. In stress situations, patients sometimes suffer a blood pressure crisis as a result. Some male patients experience ejaculation difficulties as a result of taking guanethidine. This is specifically aspermatism, whereby ejaculation fails to occur due to a lack of production of seminal fluid. In this case, the active ingredient guanethidine affects the sex glands such as the prostate gland, thereby preventing the production of secretions. However, this is basically a reversible side effect of the active ingredient guanethidine. In addition to potential side effects, the interactions of guanethidine with other substances should also be noted. The active ingredient methylphenidate may reduce the hypotensive effect of the drug. However, in some cases, methylphenidate also increases the sympathomimetic effect of the drug guanethidine at the beginning of its use. For pregnant and lactating women, special rules apply to the administration of guanethidine to avoid side effects to the child.
