Anticholinergic Drugs

Anticholinergic Drugs

Anticholinergic drugs block the action of acetylcholine, a neurotransmitter. These drugs are used to treat various conditions, including overactive bladder, Parkinson’s disease, and certain respiratory disorders. These drugs have many side effects and contraindications particularly in older adults.

Functions of Acetylcholine in Our Body

Acetylcholine (ACh) is a vital neurotransmitter that controls muscle contraction, regulating both voluntary skeletal movements and involuntary smooth muscle activity in organs like the intestines and heart. It also plays a crucial role in the central nervous system, supporting functions like memory, learning, attention, and sleep cycles, particularly REM sleep. In the periphery, ACh stimulates glandular secretions such as tears, saliva, and digestive juices, and influences blood pressure and heart rate. 

Functions in the Peripheral Nervous System

• Muscle Contraction: ACh triggers the contraction of skeletal muscles, essential for voluntary movement. 
• Organ Function: It regulates the smooth muscles of internal organs, increasing activity in the digestive system (e.g., intestinal peristalsis) and bladder. 
• Heart and Blood Vessels: ACh can slow the heart rate and is involved in the dilation of blood vessels, affecting blood pressure. 
• Glandular Secretion: It stimulates various glands to release substances like tears, saliva, sweat, and digestive fluids. 
• Reproductive Functions: ACh plays a role in processes such as erection. 

Functions in the Central Nervous System

• Memory and Learning: ACh is critical for the formation and retrieval of memories, enhancing cognitive functions like attention. 
• Motivation: It is associated with motivation and drive in the brain. 
• Sleep: ACh is essential for initiating and maintaining REM (Rapid Eye Movement) sleep. 

Impact of Imbalances

• Low ACh levels: are linked to cognitive impairments like Alzheimer’s disease. 
• High ACh levels: can cause excessive muscle contraction, leading to symptoms such as muscle spasms, paralysis, increased saliva, and blurry vision. 

Anticholinergic Drug List

Examples of Anticholinergic Drugs: 

• Atropine: Used for various purposes, including treating bradycardia (slow heart rate), dilating pupils for eye exams, and as an antidote for nerve agent poisoning. 
• Scopolamine: Primarily used for motion sickness and postoperative nausea and vomiting. 
• Benztropine: Used to treat Parkinson’s disease symptoms and drug-induced movement disorders. 
• Glycopyrrolate: Used to reduce saliva and other secretions during surgery, and also for overactive bladder. 
• Trihexyphenidyl: Used to treat Parkinson’s disease and drug-induced movement disorders. 
• Diphenhydramine (Benadryl): A common antihistamine that can also be used to treat insomnia and allergies. 
• Oxybutynin: Used to treat overactive bladder. 
• Tricyclic antidepressants: Certain types, like amitriptyline, have anticholinergic effects. 
• Antipsychotics: Some, like quetiapine, also have anticholinergic effects. 
• Antihistamines (some): Such as chlorpheniramine, cyproheptadine, and doxylamine. 
• Other: Clidinium, flavoxate, orphenadrine, and many more. 

Indications of Anticholinergic Drugs

• Overactive Bladder: Anticholinergics help relax the bladder muscles, reducing urinary frequency and urgency. 
• Parkinson’s Disease: They can help manage tremors and rigidity associated with Parkinson’s. 
• Respiratory Disorders: Used to relax bronchial muscles, aiding breathing in conditions like COPD. 
• Gastrointestinal Issues: Can help with conditions like peptic ulcers and irritable bowel syndrome. 
• Ophthalmology: Used to dilate pupils for certain eye exams and procedures. 
• Allergies: Some antihistamines with anticholinergic properties can help with allergic rhinitis. 
• Excessive Sweating: Certain anticholinergics are used to reduce sweating. 

Contraindications of Anticholinergic Drugs

• Narrow-angle glaucoma: Anticholinergics can worsen this condition by increasing pressure in the eye. 
• Urinary retention: They can exacerbate difficulty urinating, especially in cases of bladder outlet obstruction. 
• Myasthenia gravis: Anticholinergics can worsen muscle weakness in this condition. 
• Severe gastrointestinal issues: Conditions like severe constipation or paralytic ileus should be avoided with anticholinergics. 
• Severe heart conditions: Use with caution in individuals with unstable heart conditions or postural hypotension (low blood pressure upon standing). 

Side Effects of Anticholinergic Drugs

• Central Nervous System: Confusion, memory problems, cognitive impairment, drowsiness, hallucinations, and delirium are potential CNS effects. 
• Peripheral Nervous System: Dry mouth, blurred vision, constipation, urinary retention, and increased heart rate are common peripheral side effects. 
• Other: Dry eyes, dizziness, difficulty urinating, heat intolerance, and potential for falls (especially in the elderly). 
• Cardiovascular: Tachycardia and potential worsening of heart failure or angina. 
• Gastrointestinal: Constipation is a common side effect. 
• Respiratory: In some cases, anticholinergics can cause respiratory depression. 
• Dementia: Long-term use of anticholinergics may be associated with increased risk of dementia. 

Antihistamines that are Anticholinergic

First-generation antihistamines have anticholinergic properties, meaning they can block the action of acetylcholine, a neurotransmitter. This can lead to various side effects, particularly in older adults. Examples of first-generation antihistamines with anticholinergic effects are Chlorphenieramine, Diphenhydramine, Doxylamine, and Promethazine.

Anticholinergic Effects of Antihistamine and Concerns

• Side Effects:Common side effects include dry mouth, blurred vision, constipation, urinary retention, and confusion. 
• Increased Risk in Older Adults:Older adults are more susceptible to these side effects and may experience cognitive impairment or an increased risk of dementia. 
• Alternative Options:Second-generation antihistamines like loratadine (Claritin), cetirizine (Zyrtec), and fexofenadine (Allegra) are generally preferred due to their reduced anticholinergic effects. 
• Medication Interactions:It’s crucial to be aware of potential interactions between anticholinergic medications, as their effects can be additive. 

Specific Antihistamines with Anticholinergic Properties

• Diphenhydramine (Benadryl): Widely used for allergies and insomnia, it has significant anticholinergic effects. 
• Chlorpheniramine (Chlor-Trimeton): Another first-generation antihistamine with anticholinergic properties. 
• Doxylamine (Unisom): Commonly found in sleep aids, it also possesses anticholinergic activity. 
• Promethazine: A first-generation antihistamine with sedative, anticholinergic, and antiemetic properties. 
• Cyproheptadine: An antihistamine with anticholinergic effects. 
• Dimenhydrinate (Dramamine): Used for motion sickness, it also has anticholinergic activity. 
• Hydroxyzine: An antihistamine with anticholinergic effects. 
• Meclizine: Used for vertigo and motion sickness, it also has anticholinergic properties.