Is an antimuscarinic (antimuscarinic) the same as an anticholinergic (anticholinergic)?

From the Guidelines

No, an antimuscarinic is not exactly the same as an anticholinergic, though they are closely related. Antimuscarinics specifically block muscarinic acetylcholine receptors, while anticholinergics are a broader class that includes antimuscarinics but also encompasses drugs that block nicotinic acetylcholine receptors. Common antimuscarinic medications include atropine, scopolamine, ipratropium, tiotropium, oxybutynin, and tolterodine, as noted in the treatment of overactive bladder 1. These drugs are used to treat conditions like overactive bladder, COPD, asthma, and motion sickness. The distinction matters clinically because antimuscarinics produce specific side effects like dry mouth, blurred vision, urinary retention, and constipation due to their selective blockade of muscarinic receptors. Understanding this difference helps clinicians predict drug effects and side effects. For example, when treating overactive bladder with oxybutynin (an antimuscarinic), patients should be warned about potential dry mouth and constipation, while a broader anticholinergic might have additional effects on nicotinic receptors affecting skeletal muscle function.

Key differences and considerations in clinical practice are highlighted by the potential risks associated with anticholinergic medications, especially in older adults, where they can contribute to cognitive decline, increased risk of falls, and other adverse effects 1. Therefore, it's crucial to approach the use of these medications with caution, considering the specific needs and vulnerabilities of the patient population.

Some of the key points to consider include:

• Antimuscarinics are used for specific conditions and have a more targeted mechanism of action compared to broader anticholinergics.
• The side effect profiles of antimuscarinics and anticholinergics can differ significantly, with antimuscarinics typically causing dry mouth, constipation, and urinary retention.
• In older adults, the use of anticholinergic medications, including antimuscarinics, should be carefully evaluated due to the potential for adverse effects on cognition and physical function.
• Clinicians should be aware of the anticholinergic burden and its implications for patient care, particularly in managing polypharmacy in older patients 1.

From the FDA Drug Label

Oxybutynin chloride exerts a direct antispasmodic effect on smooth muscle and inhibits the muscarinic action of acetylcholine on smooth muscle. Oxybutynin chloride exhibits only one fifth of the anticholinergic activity of atropine on the rabbit detrusor muscle, but four to ten times the antispasmodic activity

• Antimuscarinic and anticholinergic are related but not exactly the same thing.
• Anticholinergic refers to the blocking of the action of the neurotransmitter acetylcholine in the central and peripheral nervous system.
• Antimuscarinic refers to the specific blocking of muscarinic acetylcholine receptors.
• The provided text suggests that oxybutynin chloride has both anticholinergic and antimuscarinic activity, but the antimuscarinic activity is more prominent 2.

From the Research

Definition and Comparison

• An antimuscarinic is a type of drug that blocks the action of the neurotransmitter acetylcholine at muscarinic receptors in the body 3, 4, 5.
• An anticholinergic, on the other hand, is a broader term that refers to any drug that blocks the action of acetylcholine at any type of cholinergic receptor, including both muscarinic and nicotinic receptors 4.
• In other words, all antimuscarinic drugs are anticholinergic, but not all anticholinergic drugs are antimuscarinic.

Mechanism of Action

• Antimuscarinic drugs work by inhibiting the binding of acetylcholine to muscarinic receptors, which are found in various tissues such as the bladder, smooth muscle, and exocrine glands 3, 5.
• This inhibition can lead to a range of effects, including relaxation of smooth muscle, reduction of secretions, and decreased bladder contractions.

Clinical Use

• Antimuscarinic drugs are commonly used to treat overactive bladder, a condition characterized by urinary urgency, frequency, and incontinence 3, 5, 6.
• They are also used to treat other conditions such as gastrointestinal disorders, respiratory disorders, and eye disorders.

Side Effects

• Antimuscarinic drugs can cause a range of side effects, including dry mouth, constipation, blurred vision, and cognitive impairment 3, 6, 7.
• The risk of cognitive impairment is a particular concern in older patients, as antimuscarinic drugs can cross the blood-brain barrier and affect cholinergic receptors in the central nervous system 6, 7.