Spinal muscular atrophy (SMA) is an inherited neurodegenerative disorder characterized by progressive muscle weakness and atrophy (shrinkage). One symptom of SMA is drooling, which is caused by jaw spasms, excessive saliva production, and difficulty swallowing.
Certain medications may help decrease drooling in SMA patients. These include amitriptyline (formerly marketed under the brand name Elavil in the U.S., where generic versions also are available), AtroPen (atropine), benztropine, Botox (onabotulinumtoxinA), Cuvposa (oral glycopyrrolate), Robinul (glycopyrrolate), and scopolamine (hyoscine). They all function by inhibiting the cholinergic system.
What is the cholinergic system?
The cholinergic system is part of the nervous system that uses the neurotransmitter, or chemical messenger, acetylcholine to transmit nerve signals. Nerve cells release neurotransmitters because of an incoming stimulus from the brain or another nerve cell.
These neurotransmitters then bind to receptors on the surface of a nearby cell. This can be another nerve cell, a muscle cell, or a gland cell. When neurotransmitters bind to muscle cells, they may trigger muscle contraction. When they bind to gland cells, they may cause the secretion of fluids such as saliva.
Amitriptyline is a medication for the treatment of depression, pain, and migraines. It acts through a number of different mechanisms. When taken orally, it blocks acetylcholine receptors in the glands that secrete saliva and thereby reduces drooling.
AtroPen is used to treat nerve agent poisoning, decrease saliva production, and reduce muscle spasms of the gastrointestinal tract, as well as urinary and gallbladder systems.
When injected into salivary glands, AtroPen blocks the action of acetylcholine by binding to its receptors on the glands and may reduce drooling.
Benztropine is an oral tablet that reduces the effectiveness of acetylcholine by blocking its receptors.
The U.S. Food and Drug Administration (FDA) approved it to treat Parkinson’s disease symptoms and tremors caused by other medications. It also is commonly used off-label to manage excessive saliva production.
Botox is a neurotoxic protein from the bacterium Clostridium botulinum. It inhibits the release of acetylcholine. When injected into the jaw or salivary glands, Botox can reduce jaw spasms and the secretion of saliva and subsequently drooling.
A recent study investigating Botox injections for drooling in patients with a number of different neuromuscular conditions found that the two patients with SMA (one with type 2 and one with type 3) had some of the most improvement in drooling on a subjective scale.
Botox is experimental in SMA patients and should be used cautiously in those with neuromuscular diseases as the neurotoxin can spread outside the injection site.
Cuvposa is an oral solution of glycopyrrolate. The FDA approved it to reduce drooling caused by neurological disorders in children, ages 3 to16.
Robinul is an anti-spasmodic agent, meaning it suppresses muscle spasms. It is also used to reduce secretions from the salivary glands, pharynx (part of the throat), trachea (windpipe), and bronchi (airways that lead to the lungs).
Robinul also acts as an anticholinergic, reducing the production of acetylcholine. In SMA patients, it is injected into salivary glands to reduce drooling.
Scopolamine, also known as hyoscine, is a patch that is normally placed on the skin behind the ear where the medication can diffuse slowly through the skin and into the bloodstream. It is another medication that blocks the activity of acetylcholine.
It is approved for preventing nausea and vomiting after surgery or from motion sickness, but may be prescribed for excessive drooling in patients with disabilities.
Last updated: March 5, 2021
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