What is an anticholinergic medication?
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 associated with activation of the parasympathetic nervous system.
In dermatology, anticholinergics are used to help control hyperhidrosis.
The most commonly prescribed anticholinergics for hyperhidrosis are:
Mechanism of action of anticholinergic medications
Anticholinergic drugs competitively inhibit binding of the neurotransmitter, acetylcholine. They target either muscarinic acetylcholine receptors or, less commonly, nicotinic acetylcholine receptors.
- Muscarinic 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 (for example, dementia).
Interactions of anticholinergic medication with other drugs
Anticholinergic medications have potential interactions with many other drugs, especially those with cholinergic actions or anticholinergic side effects. They are best avoided when taking another anticholinergic medication.
Anticholinergic effect is enhanced by:
- Antidepressants, including amitriptyline, nortriptyline, paroxetine, fluoxetine and monoamine oxidase inhibitors (MAOI)
- Antihistamines used to treat asthma, hay fever and urticaria
- Tiotropium, ipratropium bromide and potassium chloride tablets.
Acetylcholinesterase inhibitors used in myasthenia gravis and Alzheimer disease can antagonise 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. They 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 5 mg twice daily. It is also effective for facial hyperhidrosis.
Glycopyrrolate is an ionised drug that targets the M3 receptors, a subset of muscarinic 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 1–2 mg 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.