INTRODUCTION
Clenbuterol , a selective β2 agonist used to treat asthma in many countries, is generally considered safe and has multiple mechanisms by which it could slow ALS progression. Patients with asthma, given 80 μg of clenbuterol , had a mild increase in the heart rate but no arrhythmia or significant electrocardiographic changes.1 2–4 Clenbuterol stimulates muscle hypertrophy by inducing the expression of insulin-like growth factor (IGF)-1 and IGF-2 and their receptors.5 Clenbuterol may also have a neuroprotection role by inducing neurotrophic growth factor biosynthesis and regulating glial function.6,7 8 clenbuterol in patients with ALS showed promising findings in improvements of limb muscle strength, forced vital capacity (FVC), and stabilization of ALS functional rating scales (ALS-FRS).4 clenbuterol -treated patients with late-onset Pompe disease, a muscle disease caused by mutation of gene encoding alpha acid glucosidase.9 clenbuterol in ALS.
METHODS
Study Design and Oversight
This was an open-label, 24-week pilot study of the safety and efficacy of oral clenbuterol in 25 patients with ALS under IND 145248. The study was approved by the Duke Institutional Review Board (Pro00103668) and conducted through the Duke ALS clinic. Clenbuterol hydrochloride (spiropent) was purchased from Boehringer Ingelheim. All the participants provided written informed consent before the screening. In-person study visits occurred at weeks 0, 4, 12 and 24, and phone visits were conducted at weeks 1, 6, 16, and 20. The drug was initiated at 40 μg daily at the week 0 visit and titrated to 40 μg twice daily at week 1. The dose was further increased to 80 μg/40 μg twice daily at the week 6 visits and 80 μg twice daily at week 7. Participants continued this dose until week 24. The selected target dose is based on the beneficial muscle effects in a Phase I/II clinical trial in patients with late-onset Pompe disease.9
Participants
The trial enrolled 25 patients with a diagnosis of possible, probable, or definite ALS according to the El Escorial criteria. There was no limitation as to the time of symptom onset. All participants were required to have FVC > 50% predicted for age, height and gender, and life expectancy of at least 6 months. If FVC testing was restricted due to COVID-19, then a most recent FVC within the past 6 months of 80% or greater was allowed. This is because most studies show FVC decline by about 2% per month in ALS and rarely at greater than 5% per month.10,11 Supplemental Digital Content (see Table 1 , https://links.lww.com/JCND/A54
Outcomes
Primary outcomes were the safety and tolerability of clenbuterol at 80 μg twice daily in patients with ALS. Safety laboratory results (complete blood count, chemistry panel, liver panel, creatinine kinase, and electrocardiogram) were obtained at in-person visits. Adverse events were systemically gathered at all times points.
Secondary outcomes included the rate of decline in the revised version of the ALS Functional Rating Score (ALSFRS-R),12,13 14,15
Statistical Analysis
Continuous data were summarized using means, medians, standard deviations, and ranges for each group and visit. Categorical data, including adverse event (AE) analysis, were summarized by using frequencies and distributions.
To test for efficacy, ALSFRS-R slopes during treatment were compared with slopes before treatment. Pretreatment slope for each participant was estimated as follows: (48-enrollment ALSFRS-R)/months since symptom onset. A similar analysis was performed for FVC, comparing the slopes of percent-predicted FVC during treatment versus the slopes before treatment. Pretreatment slope for each participant was estimated as follows: (100%-enrollment percent predicted FVC)/months since symptom onset. Slope comparisons included means (by t tests) as well as within-individual slopes (by paired t tests). Myometry scores were compared graphically between baseline and week 24.
RESULTS
Enrollment and Retention
Enrollment and protocol adherence were challenged by the COVID-19 pandemic; our institution would not allow new study enrollment between March 12, 2020, and June 15, 2020, and FVC measurements were deemed unsafe for several months as well. Nonetheless, 25 patients meeting eligibility criteria were enrolled between February 10, 2020, and September 1, 2020. Participants had a mean age of 59 years and a mean disease duration of 43 months. Forty-eight percent of participants were female. Sixty-eight percent of participants were taking riluzole, and none were taking edaravone (Table 1 ). Fourteen participants withdrew early from the study, and the withdrawal time was included in Supplemental Digital Content (see Table 2 , https://links.lww.com/JCND/A54
TABLE 1. -
Demographics and Characteristics of Participants
Mean (SD) or Frequency
Age (y)
59.20 (11.38)
% Female
48
Duration of ALS (mo)
42.56 (39.02)
ALSFRS-R (at enrolment)
34.08 (4.56)
FVC volume (at enrolment)
3.01 (0.96)
FVC % predicted (at enrolment)
76.99 (19.22)
Riluzole (% yes)
68
Adverse Events
Two participants experienced severe adverse events (SAEs), but neither was related to clenbuterol treatment. Among the SAEs, one participant had a near-drowning accident and the other participant had pulmonary emboli. Twenty-four participants experienced nonserious AEs. The most common AE were jitters, tremors, cramps and spasticity, and insomnia, which were the main reasons for the discontinuation of the trial. A complete list of AEs is provided in Table 2 . No concerning safety laboratory or electrocardiogram changes occurred over the course of the study.
TABLE 2. -
Severe Adverse Events and Adverse Events
Name
No. of Participants Experiencing
AE or SAE
Near drowning
1
SAE
Pulmonary emboli
1
SAE
Jitters/tremors
10
AE
Cramps/spasms
8
AE
Insomnia
7
AE
Stiffness/spasticity
6
AE
Elevated liver transaminases
3
AE
Increased work of breathing
2
AE
Decreased appetite/weight loss
2
AE
Gastrointestinal upset/nausea
2
AE
Headache
2
AE
Palpitations
1
AE
Elevated creatine kinase
1
AE
Hyperglycemia
1
AE
Elevated prostate-specific antigen
1
AE
Tooth removal
1
AE
Pruritus
1
AE
Foot pain
1
AE
Restless legs
1
AE
Tendinitis
1
AE
Nasal congestion
1
AE
Hot flashes
1
AE
Dizziness/instability
1
AE
Increased fasciculation
1
AE
Anxiety
1
AE
Electrocardiogram changes
1
AE
Elevated T4
1
AE
Tachycardia
1
AE
Constipation
1
AE
Urinary tract infection
1
AE
Accelerated disease progression
1
AE
Efficacy Per-Protocol
For the 11 patients who completed 24 weeks of treatment, all had slower ALSFRS-R progression during clenbuterol treatment compared with before it was started; one of these had no progression during 6 months of clenbuterol treatment, and 4 others regained lost points over the 6-month treatment period. The mean ALSFRS-R slope was −0.17 during the 24 weeks of treatment, which was significantly slower than the pretreatment mean slope −0.56 (P = 0.045) (Fig. 1 ). The pretreatment and post-treatment ALSFRS-R slopes of each patient were delineated in Table 3 . The within-individual ALSFRS-R slopes before treatment were also significantly different from the slopes during the 6 months of treatment (P = 0.0049).
FIGURE 1.: Compare the mean ALSFRS-R slopes preclenbuterol and postclenbuterol treatment of the 11 participants who completed all 24 weeks of the study. The mean ALSFRS-R slope post-treatment was significantly slower than the pretreatment mean slope (P = 0.045).
TABLE 3. -
Within-Individual ALS-FRSR Slopes Pretreatment and Post-treatment
Participant ID
Pretreatment Slope
During-Treatment Slope
Slope Difference
2*
−0.21
−0.10
0.11
3
−0.37
−0.13
0.24
5*
−0.20
0.12
0.32
6*
−1.13
−0.34
0.80
7
−0.19
0.00
0.19
8*
−0.29
−0.24
0.05
10*
−0.23
0.03
0.26
11*
−0.23
0.00
0.23
13
−0.11
−0.25
−0.14
14*
−0.24
−0.20
0.04
16*
−1.00
−0.59
0.41
18
−0.94
−0.63
0.31
19
- 0.63
−0.75
−0.12
20
−0.41
−1.50
−1.09
21
−0.50
−0.09
0.41
23
−0.50
−0.59
−0.09
24*
−1.88
−0.59
1.28
25*
−0.49
0.01
0.49
26*
−0.32
0.05
0.37
27
−0.57
−0.86
−0.29
* Eleven participants who completed 24 weeks of treatment.
For these same 11 patients who completed all 6 months of the study, 10 had at least 2 FVC measurements (see Table 2 , Supplemental Digital Content , https://links.lww.com/JCND/A54 P = 0.22) (Fig. 2 ). The pretreatment and post-treatment FVC slopes of each patient were shown in Table 4 . The within-individual FVC slopes before treatment were not significantly different from the slopes during the 6 months of treatment (P = 0.22).
FIGURE 2.: Compare the mean percent predicted FVC slopes preclenbuterol and postclenbuterol treatment of the 10 participants who completed 24 weeks of the study and had at least 2 FVC measurements. The mean percent predicted FVC slope was slower post-treatment compared with pretreatment, but the difference was not statistically significant (P = 0.22).
TABLE 4. -
Within-Individual FVC Slopes Pretreatment and Post-treatment
Participant ID
Pretreatment Slope
During-Treatment Slope
Slope Difference
2*
−0.06
−0.56
−0.50
3
−1.40
−0.34
1.06
5*
−1.82
1.18
3.00
6*
−3.31
−0.85
2.46
7
0.03
0.75
0.72
8*
−0.69
−0.87
−0.18
10*
−0.77
0.92
1.69
14*
−0.71
0.46
1.17
16*
−1.50
−0.67
0.83
18
−2.31
−0.75
1.56
21
−0.10
0.88
0.98
23
−0.68
1.50
2.18
24*
0.32
−1.49
−1.82
25*
−0.24
−0.28
−0.04
26*
0.02
−0.38
−0.40
27
−0.87
−1.00
−0.13
* Ten participants who completed 24 weeks of treatment and had at least 2 FVC measurements.
Efficacy Intention to Treat
Intention-to-treat analyses were performed for 20 participants who had at least one ALSFRS-R measurement post-treatment (see Table 2 , Supplemental Digital Content , https://links.lww.com/JCND/A54 Table 4 ). The mean pretreatment ALSFRS-R slope was −0.52, and the mean post-treatment slope was −0.33. This difference was not statistically significant (P = 0.16) (Fig. 3 ). The within-individual ALSFRS-R slope differences were not statistically significant (P = 0.08).
FIGURE 3.: Compare the mean ALSFRS-R slopes preclenbuterol and postclenbuterol treatment of the 20 participants who had at least 1 ALSFRS-R score measured postbaseline. There was no significant difference between the mean pretreatment and post-treatment slopes (P = 0.16).
There were 16 patients who had at least 2 FVC measurements (see Table 2 , Supplemental Digital Content , https://links.lww.com/JCND/A54 P = 0.02) (Fig. 4 ). The within-individual FVC slopes before treatment were significantly different from the slopes during the 6 months of treatment (Table 4 ) (P = 0.02).
FIGURE 4.: Compare the mean percent predicted FVC slopes preclenbuterol and postclenbuterol treatment of the 16 participants who had at least 2 FVC measurements. The difference between mean pretreatment and post-treatment slopes was statistically significant (P = 0.02).
Myometry
Myometry data were highly variable between patients, both from a starting point and for how these changed over time. Graphical comparisons suggested that most participants became weaker over the 6-month trial. However, at least some participants appeared to get significantly stronger over time in the trial, which is unusual in the natural history of ALS (Fig. 5 ).
FIGURE 5.: Selected myometry graphs from the 11 participants who completed the 24-week study. These data show a lot of variability between participants, but some participants did seem to get stronger over the course of the study. LE, lower extremity; MVC, maximum voluntary contraction; UE, upper extremity.
DISCUSSION
Our study confirms clenbuterol is safe for selected patients with ALS, but it was less tolerable at the doses we chose compared with an earlier Italian case series, in which 16 patients were treated with 60 μg daily.4 8 4
Our study is limited by a small sample size, large dropout rate, lack of randomization, and blinding and placebo controls. Hence, a conclusion could not be drawn regarding the efficacy of clenbuterol . Our comparisons of ALSFRS-R and FVC slopes during treatment with those calculated before treatment assumes that disease progression on these measures is fairly linear over the observation periods; this is debatable.16 clenbuterol dosing, tolerability, and safety. A large-scale clinical trial is now warranted to determine its potential efficacy.
ACKNOWLEDGMENTS
This study was supported by donations from one patient's family for which the authors are grateful. The authors are also grateful for to the participants for their time and effort.
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