Sympatholytics: Drugs that Antagonize the Sympathetic Nervous System

Sympatholytics

Sympatholytics, also known as antiadrenergics, are a class of drugs that antagonize the effects of endogenously released epinephrine and norepinephrine, as well as exogenously administered drugs. They act on the sympathetic nervous system, which is responsible for the body's "fight or flight" response, by blocking the actions of adrenergic postganglionic fibers.

The sympathetic nervous system is a part of the autonomic nervous system and plays a crucial role in controlling various physiological processes, such as heart rate, blood pressure, and respiration. When the body is under stress or in danger, the sympathetic nervous system activates the "fight or flight" response, increasing heart rate, blood pressure, and respiration, and diverting blood flow away from the digestive system to the muscles.

Sympatholytics are used to treat conditions where excessive activity of the sympathetic nervous system is problematic. For example, in hypertension, excessive sympathetic outflow can contribute to high blood pressure. By blocking the actions of adrenergic postganglionic fibers, sympatholytics can help reduce blood pressure and restore normal physiological function.

There are several types of sympatholytics, including drugs that act on different types of adrenergic receptors. For instance, beta-blockers, such as propranolol, bind to beta-adrenergic receptors and block the effects of adrenaline on the heart, reducing heart rate and blood pressure. Alpha-blockers, such as phenylephrine, act on alpha-adrenergic receptors and are used to treat hypertension and urinary incontinence.

In addition to their use in hypertension, sympatholytics are also used in anesthesia to control blood pressure during surgery. They may also be used to manage the "fight or flight" response in certain clinical conditions, such as sepsis, where excessive sympathetic activity can exacerbate the inflammatory response and worsen the patient's condition.

However, it's important to note that sympatholytics can have side effects and interact with other medications. For example, beta-blockers can cause bradycardia (slow heart rate) and may worsen asthma symptoms. Alpha-blockers can cause hypotension (low blood pressure), dizziness, and syncope (fainting). Therefore, it's crucial to monitor patients closely and adjust the dosage and type of sympatholytic appropriately.

In summary, sympatholytics are a class of drugs that antagonize the effects of adrenergic postganglionic fibers, helping to manage excessive sympathetic nervous system activity in various conditions, such as hypertension and sepsis. They are used to control blood pressure during surgery and can have side effects that require careful monitoring.