Review study evaluates botulinum for treating excessive drooling

Botulinum was safe, effective when injected into salivary glands to prevent sialorrhea

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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Botulinum toxin was found to be relatively safe and effective for treating excessive drooling in people with Parkinson’s disease, according to a recent systematic review and meta-analysis of previous clinical trials.

While side effects usually were mild, the researchers believe larger and longer studies are needed to establish the safety of this treatment approach.

The study, “The effectiveness and safety of botulinum toxin injections for the treatment of sialorrhea with Parkinson’s disease: a systematic review and meta-analysis,” was published in BMC Pharmacology and Toxicology.

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In Parkinson’s, difficulty controlling the muscles in the face and mouth can cause symptoms of excessive drooling, or sialorrhea. Studies indicate that more than 80% of patients may experience this symptom, according to researchers.

Botulinum is a substance that blocks the release of a chemical called acetylcholine from the nerve cells involved in muscle contractions. It is a potent neurotoxin, but various forms of it are used in small doses for cosmetic and medical purposes.

While its best-known use is a cosmetic one — injections help relax the face muscles and prevent wrinkles — the toxin also can prevent excessive drooling when injected into the salivary glands, and that’s why it is used to treat sialorrhea, including in people with Parkinson’s.

Brands approved in the U.S. for sialorrhea include Myobloc (rimabotulinumtoxinB) and Xeomin (incobotulinumtoxinA).

Still, the evidence backing the use of the medication for sialorrhea in Parkinson’s comes from a number of small studies, each involving a low number of patients.

“Many studies now show that Botulinum toxin has value in treating Parkinson-related saliva, while others suggest that it is less effective,” the researchers wrote.

Review included eight smaller studies

In the recent study, researchers conducted a systematic review and pooled analysis of previous placebo-controlled clinical trials in an effort to get a broader sense of botulinum’s safety and efficacy for these people.

The eight included studies were conducted in the U.S., Italy and Estonia, cumulatively involving 259 Parkinson’s patients. Botulinum type A was evaluated in five studies, whereas type B was tested in three.

Types A and B, with a similar mechanism, are the two forms of the toxin approved for use in humans. The doses of either varied, and most studies evaluated the effects on drooling after one month, using the Drooling Severity Frequency Scale (DSFS).

Analyses indicated a significant reduction in DSFS scores — reflecting a reduction in drooling — with botulinum toxin compared to placebo across evaluable studies, with no significant difference in effect between types A and B.

Overall, “the results provide a new understanding of the effectiveness of [botulinum] injection on sialorrhea with [Parkinson’s],” the researchers wrote.

The scientists believe the findings support the use of botulinum for this indication, particularly in light of the fact that physical therapy is time-consuming and other medications, such as acetylcholine blockers, have significant side effects.

Most side effects mild or moderate

A higher rate of side effects was observed with botulinum than placebo, but most side effects were mild or moderate in severity. No serious side effects were considered related to the treatment.

Dry mouth was the most common side effect associated with the treatment, with others including neck pain, diarrhea, and worsened gait. Recovery time from side effects ranged from one to six weeks.

Still, it is important to consider the safety of botulinum, the scientists emphasized, especially considering the short-term nature of the studies. Long-term use of botulinum has been associated with a reduction in salivary gland size, difficulty swallowing, and oral health deteriorations.

“Larger samples and more scientifically designed randomized controlled trials are needed to explore the safety of botulinum toxin as a potential alternative treatment for sialorrhea caused by [Parkinson’s],” the researchers wrote.

More work also is needed to understand the best dose, treatment duration, and mode of delivery for botulinum, as well as the mechanisms through which sialorrhea arises in Parkinson’s.