Salbutamol may improve upper limb strength in SMA children: Study
Treatment offers low-cost option for patients in underdeveloped regions
The use of salbutamol may safely improve upper limb strength, as well as provide other benefits, in people with spinal muscular atrophy (SMA), particularly among young children, according to data from a new meta-analysis — though the researchers noted that controlled studies are needed to confirm these findings.
Two children with SMA given the oral medication reached new milestones, the team found, with the researchers noting that “salbutamol has been shown to improve respiratory function and contribute to weight gain in certain younger individuals.”
These analysis findings suggest that use of salbutamol offers a “cost-effective and viable option” for patients where newer, more expensive treatments aren’t available, the researchers wrote in a “What is New” section of the study’s abstract.
“Salbutamol represents a safe therapeutic option that holds considerable promise in the management of SMA,” the researchers wrote, noting the medication’s relevance for “patients in underdeveloped regions who lack access to or cannot afford disease-modifying treatments.”
The resulting study, “Salbutamol in 5q spinal muscular atrophy: a systematic review and meta-analysis of efficacy and safety,” was published in the European Journal of Pediatrics by researchers in China.
SMA is mainly caused by mutations in the SMN1 gene, which codes for a protein called SMN. Without enough of this protein, motor neurons — the specialized nerve cells that control voluntary movement — become damaged. As a result, muscles stop receiving proper signals from motor neurons, gradually weakening over time.
Salbutamol is a medication that helps muscles relax. While commonly used to treat asthma, it has also been prescribed to support breathing in children with SMA.
It is thought that salbutamol increases production of SMN from the SMN2 gene. Normally, SMN2 produces only about 10% as much functional SMN protein as the SMN1 gene due to a slight difference in the genetic sequence. Patients with more copies of SMN2 usually have milder disease symptoms.
Analysis looked at safety, efficacy of salbutamol in SMA children, adults
In this study, researchers from three Chinese institutions sought to better understand how safe and effective salbutamol is for children and adults with SMA. The team combined data from eight studies involving 154 patients. One patient was diagnosed with SMA type 1, 106 with SMA type 2, and 47 with SMA type 3. All were prescribed oral salbutamol at a daily dose of 6 to 12 mg.
Many of these patients reported that they felt better while using salbutamol, with benefits that included less fatigue, increased endurance, and improved swallowing. Fewer respiratory infections also were found to occur among patients. Further, two studies noted weight gain in younger individuals.
Two children experienced improvements in motor milestones after one year of salbutamol treatment. One was able to sit independently and the other to walk unassisted. Before treatment, they could only do so with assistance.
A closer look at two studies found that children younger than age 6 showed clear gains in upper limb strength. This was measured using a standard clinical scale called the Revised Upper Limb Module (RULM). The average improvement was 3.89 points, which was significant, according to the researchers.
The increases in RULM scores were maintained at both the 12-month and 18-month follow-up assessments, which was particularly notable in younger patients. One study also found more pronounced increases in Hammersmith Functional Motor Scale – Expanded scores of motor function among patients younger than 6.
Gains in motor function seen among treated patients
Across four studies, salbutamol therapy did not improve lung function over six to 12 months. However, in another study, treatment for at least one year did improve measures of respiratory function and of respiratory muscle strength in patients with type 2 SMA.
Salbutamol also increased the levels of full-length SMN2 transcripts, the genetic instructions for producing the SMN protein, the researchers noted. The increase was statistically significant at six months and stayed high after 12 months of treatment, the data showed.
Overall, the “meta-analysis … revealed that motor function of SMA patients improved following salbutamol treatment,” the researchers wrote, noting “statistically significant improvements” on some assessments.
Three patients discontinued salbutamol treatment due to adverse reactions, namely hand tremors, dizziness, and skin redness. Generally, side effects during treatment were mild and resolved spontaneously.
Salbutamol, given its accessibility, affordability, and favorable safety profile, offers notable value to SMA patients.
Given the “lifelong necessity” of treatments, “medications that enhance muscle strength hold considerable research potential,” the team wrote.
The researchers also noted that, in many regions, new — and higher-priced — disease-modifying treatments for SMA may not be available to many patients.
“Salbutamol, given its accessibility, affordability, and favorable safety profile, offers notable value to SMA patients,” they wrote.
Still, “further studies are essential to rigorously validate [salbutamol’s] efficacy and safety, elucidate its biological effects, and determine personalized application strategies for different SMA subgroups,” the researchers concluded.
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