Atropine for spinal muscular atrophy

Last updated Feb. 18, 2025, by Margarida Maia, PhD
Fact-checked by Jose Lopes, PhD

What is atropine for SMA?

Atropine, also known as atropine sulfate, is an anticholinergic medication available as eye drops that can also be applied under the tongue or as a solution for injection into a muscle or vein, or under the skin.

It is used in adults and children to reduce the amount of saliva that builds up in the respiratory tract during surgery, as an antidote to insecticide or mushroom poisoning, and in emergencies to restore a normal heartbeat when the heart slows or stops. Eye drops are used before eye examinations to dilate the pupil, the black opening in the center of the eye, and to relieve pain caused by eye inflammation.

Sublingual atropine, applied as drops under the tongue, may also sometimes be used off-label to reduce excessive drooling when a neuromuscular disease like spinal muscular atrophy (SMA) weakens the muscles around the mouth and throat, causing difficulty swallowing and leading to saliva pooling that overflows as drool. In SMA, muscle weakness gets progressively worse over time.

Atropine was once marketed in the U.S. by Meridian Medical Technologies as a single-dose auto-injector for into-the-muscle injection under the brand name AtroPen. The pen and its generic alternatives have been discontinued and are no longer available.

Therapy snapshot

How does atropine work?

SMA causes weakness in skeletal muscles, the muscles used for movement. It can also cause bulbar weakness, which affects the muscles around the mouth and throat. Bulbar weakness causes loss of control over the mouth, which can result in difficulty swallowing. This can lead to sialorrhea (excessive drooling), which occurs when saliva pools in the mouth and flows out. In some cases, excess saliva can be aspirated into the lungs, causing choking or pneumonia.

Like most other medications that reduce saliva production, atropine is an anticholinergic that works by blocking the effects of the parasympathetic nervous system, which controls bodily functions such as the heartbeat. It does this by competing with acetylcholine at its receptors. Acetylcholine is a chemical messenger that nerve cells release to communicate with other cells. When applied under the tongue, atropine is expected to prevent acetylcholine from activating its receptors on the glands that produce saliva, reducing excessive drooling.

How is atropine administered?

Atropine is available as eye drops that can also be applied under the tongue, or as a solution for injection into a muscle or vein or under the skin.

While atropine is not indicated as an SMA treatment, the recommended dose for use as an antisialagogue — that is, to reduce saliva — is 0.5 mg to 1 mg that may be given as an injection 30 to 60 minutes before surgery and repeated as needed every 4 to 6 hours up to a maximum total of 3 mg. The maximum total dose is 1 mg for children younger than 12, and twice as much (2 mg) for those 12 and older.

In the few studies reporting on the use of sublingual atropine to reduce excessive drooling in patients, doses ranged from 1 to 3 drops given at a time, and frequency ranged from every 4 to 24 hours, or as needed. In one study in children, including a 6-month-old boy with SMA type 2, sublingual atropine was given at 20 micrograms per kilogram of body weight, 4 to 6 times in a day, for seven days.

Common side effects of atropine

Common side effects occurring with long-term use of atropine at the prescribed doses for the approved indications may include:

• dry mouth
• blurred vision
• photophobia (light sensitivity)
• rapid heartbeat.

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