Background Bromhexine is a potent inhibitor of transmembrane serine protease 2 and appears to have an antiviral effect in controlling influenza and parainfluenza infection; however, its efficacy in COVID-19 is controversial.

Methods A group of hospitalized patients with confirmed COVID-19 pneumonia were randomized using 1:1 allocation to either standard treatment lopinavir/ritonavir and interferon beta-1a or bromhexine 8 mg four times a day in addition to standard therapy. The primary outcome was clinical improvement within 28 days, and the secondary outcome measures were time to hospital discharge, all-cause mortality, duration of mechanical ventilation, the temporal trend in 2019-nCoV reverse transcription-polymerase chain reaction positivity and the frequency of adverse drug events within 28 days from the start of medication.

Results A total of 111 patients were enrolled in this randomized clinical trial and data from 100 patients (48 patients in the treatment arm and 52 patients in the control arm) were analyzed. There was no significant difference in the primary outcome of this study, which was clinical improvement. There was no significant difference in the average time to hospital discharge between the two arms. There were also no differences observed in the mean intensive care unit stay, frequency of intermittent mandatory ventilation, duration of supplemental oxygenation or risk of death by day 28 noted between the two arms.

Conclusion Bromhexine is not an effective treatment for hospitalized patients with COVID-19. The potential prevention benefits of bromhexine in asymptomatic postexposure or with mild infection managed in the community remain to be determined.