What are anticholinergic medications?
Anticholinergic medications are a class of drug that block the neurotransmitter acetylcholine in the central and peripheral nervous system. They are used to treat a wide variety of conditions. In dermatology, anticholinergics are used to help control hyperhidrosis.
The most commonly prescribed anticholinergics for hyperhidrosis are:
- oxybutynin (Ditropan®)
- glycopyrrolate (Robinul®)
- propantheline (Pro-banthine®).
Mechanism of action of anticholinergic medications
Anticholinergic drugs competitively inhibit binding of the neurotramsmitter, acetylcholine. They target either muscuranic acetylcholine receptors or, less commonly, nicotinic acetylcholine receptors.
- Muscuranic receptors are found on nerve endings to smooth muscles cells, secretory glands and the eye. They are also found in the central nervous system.
- Nicotinic acetylcholine receptors are located at the nerve endings of neuromuscular junctions and are the target of muscle relaxing drugs.
Adverse effects of anticholinergic medications
Side effects of anticholinergics include:
- Dry mouth
- Blurred vision
- Dry eyes
- Urinary retention
- Dizziness due to drop in blood pressure on standing up (postural hypotension)
- Cognitive problems (confusion)
- Heart rhythm disturbance
Side effects from anticholinergics are relatively common, especially in the elderly, and frequently lead to discontinuation of their use.
Anticholinergics should be used with caution in people with:
- Unstable heart conditions
- Postural hypotension
- Chronic constipation
- Atonic bowel
- Severe colitis
- Urinary obstruction
- Cognitive impairment (e.g., dementia)
Interactions of anticholinergic medications with other drugs
Anticholinergic medications have potential interactions with many other drugs, especially those with cholinergic actions or anticholinergic side effects.
- Antidepressants, such as amitriptyline (Amitrip®), nortriptyline (Norpress®), paroxetine (Aropax®), fluoxetine (Prozac®) and monoamine oxidase inhibitors (MAOI), have anticholinergic side effects. They are best avoided when taking an anticholinergic medication.
- Acetylcholinesterase inhibitors are used in myasthenia gravis and Alzeihmer disease. They can antagonise the action of anticholinergic medications.
- Antihistamines, used to treat asthma, hay fever and urticaria, also have anticholinergic side effects,
- Other drugs such as tiotropium (Spiriva®), ipratropium bromide (Atrovent®) and potassium chloride tablets can enhance the action of anticholinergic medications.
Anticholinergics in pregnancy
Most anticholinergics are pregnancy category B2. This means that safety in pregnancy has not been well established. Therefore, the drug should not be used in pregnant women or those likely to become pregnant, unless the expected benefits outweigh any potential risk.
Anticholinergics for hyperhidrosis
Oxybutinin is the best studied agent used for excessive sweating. It has proven to be effective for palmar and axillary hyperhidrosis in 50% of patients treated with 5mg twice daily. It is also effective for facial hyperhidrosis.
Glycopyrrolate is an ionized drug that targets the M3 receptors, a subset of muscuranic receptors found in glandular tissue. It has a lower incidence of neurological and ocular side effects compared with other anticholinergics. Glycopyrrolate is available as topical and oral formulations.
- Topical glycopyrrolate comes in a 0.5%, 1% or 2% strengths and is applied to the affected skin daily. Studies of patients with craniofacial and gustatory hyperhidrosis have shown this to be effective for most patients. Although well tolerated, the 2% strength was associated with headache and dizziness in some people.
- Oral glycopyrrolate is effective for palmar, plantar, axillary and craniofacial hyperhidrosis. Usual dosing is 1-2mg once or twice daily. In a retrospective study glycopyrrolate was effective in two thirds of patients although one quarter of patients had to discontinue the medication due to adverse effects.
Propantheline can be used topically and orally to treat hyperhidrosis. The dose is 15-30 mg four times per day. Introduced in the 1970s, there are no contemporary studies evaluating propantheline for hyperhidrosis.