How Do Muscarinics Like Atrovent Work?

In a previous post, I described how beta adrenergics like albuterol work. In this post I will describe how muscarinics like Atrovent and Spiriva work. Here’s what to know:

Autonomic Nervous System

This is a system controlled by your brain. It contains a series of nerves and neurotransmitters. It’s how your brain responds to your environment. It contains two parts.

  1. Sympathetic Nervous System (SNS). It’s often called the “Fight or Flight” system. It’s how your body responds to danger. It constricts blood vessels. It increases the rate and force of the heart. It opens airways. This is to increase the flow of oxygen and blood through your body. It’s to prepare you to respond to some stress in your environment. Medicines that mimic the SNS to open airways are albuterol (Ventolin) and levalbuterol (Xopenex). I describe this in more detail in my post, “How Does Albuterol Work?”
  2. Parasympathetic Nervous System (PNS). This is the system that returns everything back to normal. After the danger passes, your brain releases a hormone called acetylcholine. It’s a neurotransmitter. It travels by nerves to your heart and lungs. It attaches to muscarinic receptors. They are sometimes called cholinergic receptors because acetylcholine is attracted to them. Para means resemble. Sympathetic means to mimic. Atrovent and Spiriva are medicines that mimic this response. Read on and I shall explain. Don’t worry. I shall keep this short and sweet.

What are muscarinic receptors?

These are receptors lining various tissues of your body. Acetylcholine is attracted to them. So, when acetylcholine is released, it binds with muscarinic receptors. Many of these receptors line bronchial smooth muscles. When stimulated, these muscles are told to constrict or spasm. Airways narrow. This is a normal response. But, overstimulation of the PNS system can cause bronchospasm. This is what happens in asthma and COPD.

What are Muscarinics?

These are medicines that are attracted to muscarinic receptors. They sit in muscarinic receptor sites and prevent acetylcholine from doing so. In return, they are said to block the effects of acetylcholine. So, for this reason, they are often called anti-cholinergics. Sometimes they are also called “back door bronchodilators.”

What do studies show?

Studies show that muscarinics may work as well, and sometimes better, than beta agonists like albuterol in COPDers.

The reason is because COPD related bronchospasm is more likely to be caused by stimulation of the PNS system compared to bronchospasm in asthma. At least this the theory. This is why muscarinics are now considered top-shelf COPD medicines and second shelf asthma-medicines. They are usually prescribed together with inhaled corticosteroids.1-4

One more note worth mentioning. Medicines like albuterol are stronger bronchodilators when compared to muscarinics. For this reason, muscarinics are said to be mild bronchodilators. Regardless, COPDers are more likely to enjoy their benefits than asthmatics. At least according to the studies I’ve reviewed.1-4

What are some muscarinic medicines?

The fumes of the belladonna plant were inhaled by ancient Egyptians. Atropine was isolated from the belladonna plant in 1867. It was used for asthma and COPD back in the 1970s to 1990s. Ipatropium Bromide (Atrovent) is a modified version of the Atropine molecule. It needs to be taken four times a day. Tiotropium bromide (Spiriva) is another version. It lasts longer, and only needs to be taken once per day. Aclidinium bromide (Tudorza), umeclidinium (Incruse), and glycopyrrolate (Seebri) are newer long-acting muscarinic options.

Ipatropium bromide is combined with albuterol in Duoneb and Combivent. Tiotropium, umeclidinium and glycopyrrolate are combined with long-acting beta agonists in Stiolto, Anoro, and Utibron inhalers. So, there are a variety of muscarinic options available for the COPD community.

What to make of this?

Many COPDers today are prescribed a muscarinic. Now you know why.

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