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.
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.
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.
Treating Parkinson’s Disease
Parkinson’s disease is a neurodegenerative disease, meaning that it causes the neurons in the brain to die off. In particular, motor neurons in the brain die off, creating tremors and difficulty moving in the patient. Anticholinergics like benztropine and trihexyphenidyl can be used to address the tremors.
Since tremors occur due to excessive acetylcholine activity, anticholinergics can relieve these symptoms, but only in patients with mild tremors. It’s important to note that the treatment only relieves the symptoms associated with Parkinson’s, and unfortunately doesn’t cure or even slow the disease.
Anticholinergic Side Effects
Although anticholinergics have some great benefits, they do have serious side effects that can affect both the body and brain. Let’s first take a look at the side effects anticholinergics might have on the body.
Side Effects in the Body
Constipation, decreased urination, and decreased salivation can occur. These are sometimes the effects desired in a patient, such as when treating diarrhea, but if not they can be unwanted side effects. In addition, pupils, which are controlled by muscles in the eye, can be overly dilated due to a lack of contraction. Blurred vision, decreased sweating, or increased heart rate can also occur.
Side Effects in the Brain
Now let’s take a look at some of the possible side effects of anticholinergics on the brain. Long-term anticholinergic use has been linked to increase risk for dementia, where brain tissue breaks down faster than usual, like during Alzheimer’s disease. Symptoms of dementia side effects include confusion, dizziness, and trouble remembering things. Older patients should not be exposed to long-term anticholinergic use because of this risk. Although acetylcholine works to control muscle movement in the body, in the brain it is involved in memory and learning. Thus, overuse of anticholinergics can lead to problems with memory, increasing the risk for dementia.
Anticholinergics are a class of drugs that block acetylcholine messages between the brain and body, preventing muscles from contracting. Acetylcholine is a neurotransmitter inside your body that allows your brain to communicate with your muscles, so when it’s being overused, anticholinergics are used when muscles contract too much. Anticholinergics can be used to treat lung disease like COPD in which their bronchioles are clogged with mucus and, along with their alveoli, lose their shape and function; irritable bowel syndrome and diarrhea; poisonings with cholinergic drugs; and light tremors in Parkinson’s disease, which is a neurodegenerative disease, meaning that it causes the neurons in the brain to die off. Side effects include decreased muscle contraction resulting in constipation, trouble urinating, dilated pupils, decreased sweating, and blurred vision.
They may also cause memory loss and confusion by increasing risk for dementia in the elderly.Medical Disclaimer: The information on this site is for your information only and is not a substitute for professional medical advice.