Sprengers 2021.

Study characteristics
Methods	13‐week parallel trial of bumetanide versus placebo
Participants	Inclusion criteria: children 7‐15 years of age clinical diagnosis of autism IQ of at least 55 Exclusion criteria: IQ < 55 psychoactive medication use < 8 weeks prior to screening visit (except chronic melatonin treatment) start of any new therapy for developmental disorder problems (e.g. cognitive behavioral therapy) comorbid neurological disorders, chronic renal disease, unstable serious illness use of nonsteroidal anti‐inflammatory drugs documented history of hyper‐sensitivity reaction to sulphonamide derivatives Location/setting: a tertiary hospital in the Netherlands Mean age: 10.5 years Mean IQ: 101 Gender: bumetanide 68% male; placebo 69% male Sample size: 47 randomised to bumetanide group, 45 randomised to placebo group Reasons for dropouts: 4 participants (2 from each group) discontinued prior to collecting the first outcome data. "One participant in the placebo arm stopped because of nonspecific somatic complaints and another because of intractable resistance to venipunctures. The two discontinued treatments in the bumetanide arm were because of inability to adhere to potassium supplementation and one because of a school crisis requiring immediate psychiatric intervention." Baseline ABC‐Irritability scores: bumetanide 14.3 (8.2); placebo 14.5 (7.9) Concomitant medications: details not provided Previous medications: 30% had received stimulants and 6% antipsychotics in the bumetanide group while 24% and 11% from the placebo group had received stimulants and antipsychotics respectively.
Interventions	Intervention (bumetanide) for 13 weeks: twice daily bumetanide liquid with a concentration of 0.5 mg/mL for 91 days (13 weeks). The mean dose of bumetanide was 0.0482 mg/kg/day. Comparator (placebo) for 13 weeks: twice daily placebo liquid with a concentration of 0.5 mg/mL
Outcomes	Primary outcomes: ABC‐I (Aman 1985) AEs Secondary outcomes: none reported Timing of outcome assessments: baseline, day 4, day 7, day 14, day 28, day 56, day 91 (endpoint)
Notes	Study start date: June 2016 Study end date: December 2018 Funding: "The study was funded by the Netherlands Organisation for Health Research and Development (ZonMw; GGG ‐ #836041015)" Conflicts of interest: some study authors received grants for other studies. Trial registry: details not provided
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The sequence was generated with restricted randomisation using permuted block design with block sizes randomly varying from 2 to 4 to 6 participants
Allocation concealment (selection bias)	Low risk	Undistinguishable medication kits were numbered accordingly by Neurochlore, the company who provided the study medication, and were shipped to the local trial pharmacy where a sealed copy of the randomisation sequence was stored for emergency unmasking.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants, parents, healthcare providers, and outcome assessors were masked for randomisation.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	To secure masking of the outcome assessors for possible (diuretic) side effects of bumetanide, medical checks and handling of AEs during the treatment and wash‐out phase were performed by a team at the paediatric nephrology department of the nearby Wilhelmina Children’s Hospital who were also masked for randomisation.
Incomplete outcome data (attrition bias) All outcomes	High risk	Modified ITT with a high (relative) number of dubious exclusions. Quote: "Outcome measures of six participants had to be excluded from analysis. One participant appeared to have started extensive dyslexia training during the medication phase. The outcomes of the other five participants were excluded because parents explicitly mentioned unreliable reporting on outcome measures due to stress of, for example, pending divorce lawsuits or conflicts to obtain access to health care provisions."
Selective reporting (reporting bias)	Low risk	Prespecified primary outcomes reported (Social Responsiveness Scale‐2 at 91 days)
Other bias	Low risk	No obvious other sources of bias