Anticholinergics: Definition, Examples & Side Effects

Anticholinergics: Definition, Examples & Side Effects
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Lesson Transcript
Instructor: Amanda Robb
In this lesson we'll learn what anticholinergics are and how they work. We'll also go over some examples of anticholinergic drugs and the diseases they are used to treat, as well as the side effects of each.

Definition of Anticholinergics and Acetylcholine

Imagine your body becoming completely rigid. You've ingested a fatal poison from eating some mushrooms during a walk in the woods. You're unable to relax any of your muscles, as if your entire body has cramped up. Even your diaphragm starts to freeze in place and you can no longer breathe. As your vision starts to fade, a doctor who happens to be hiking with you gives you a shot of an anticholinergic to save your life.

The poison you ingested works on a natural chemical in your body called acetylcholine, which makes your muscles contract. Luckily, you had an anticholinergic to reverse the effects. Before we get into more uses for anticholinergics, let's review what acetylcholine does in the body.

Acetylcholine is a neurotransmitter inside your body that allows your brain to communicate with your muscles. All muscles - even the ones you don't actively move, like your diaphragm, which controls your lungs - need acetylcholine to keep contracting. Nerve cells called motor neurons form connections with your muscles. These nerve cells release acetylcholine, which attaches to small proteins called receptors on the outside of the muscle cells. When the acetylcholine reaches the receptors, the receptors initiate a chain reaction inside the cell to cause muscle contraction. When the acetylcholine goes away, the muscle cells stop contracting.

Small spheres called vesicles release neurotransmitters to talk to muscle cells
neurotransmitter

Anticholinergics are a type of drug designed to inhibit the signals of acetylcholine, preventing muscles from contracting. Although in excess this can be a bad thing, anticholinergics can be used to treat a variety of diseases.

Treating Lung Disorders

Anticholinergics are a second-tier drug to fight chronic lung disease, like chronic obstructive pulmonary disease (COPD) and some severe cases of asthma. The lungs are composed of two large tubes called bronchi that branch into smaller tubes called bronchioles and eventually end at the tiny air sacs called alveoli. When someone is suffering from the previously-mentioned lung disease called COPD, their bronchioles are clogged with mucus and, along with their alveoli, lose their shape and function. The bronchi also become constricted, with the muscle bands around them cinching unnecessarily. As you can see, part of the problem in this disease is overactive muscle - the muscle around the bronchi. Since we need the muscle to relax, anticholinergics can be of service.

Airways in COPD over constrict
COPD symptoms

Short-term anticholinergics, like ipratropium bromide and oxitropium bromide, are named this way because they only work for about 6 to 8 hours at a time, but with them patients can expect to feel relief in about 15 minutes. There's one long-term anticholinergic used for COPD, called tiotropium, which lasts for 24 hours and is taken as a tablet. Patients can take one tablet per day.

Treating Intestinal and Toxic Problems

Irritable bowel syndrome (IBS) and other diseases that lead to severe diarrhea can be treated with anticholinergics as well. Anticholinergics like hyoscyamine relax the smooth muscle of the intestines, relieving cramps and preventing excess movement of food, which is what causes diarrhea. Diarrhea may not sound dangerous, but in excess it can cause severe dehydration.

Anticholinergics can be used to counteract poisons that over activate the acetylcholine receptors. These poisons cause the muscles to stay in a contracted position, and the patient dies from suffocation because the diaphragm can't relax enough to let the lungs release carbon dioxide. These poisons can come from mushrooms, nerve gases, or some pesticides, and are mostly treated with atropine, an anticholinergic isolated from the deadly nightshade plant.

Atropine is an anticholinergic isolated from the deadly nightshade plant
deadly nightshade

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