Limosilactobacillus reuteri DSM‐17938 for preventing cough in adults with mild allergic asthma: A double‐blind randomized placebo‐controlled cross‐over study

Abstract Background Cough is a common troublesome symptom in asthma which is neuronally mediated. Limosilactobacillus reuteri DSM‐17938 ( L . reuteri DSM‐17938) is a probiotic shown to be effective in pre‐clinical models at suppressing neuronal responses to capsaicin, a transient receptor potential vanilloid agonist (TRPV1). Objective Investigate the effects of DSM‐17938 versus matched placebo on capsaicin‐evoked coughs in mild allergic asthmatics. Methods We performed a 4‐visit, randomized, double‐blind, placebo‐controlled, two‐way cross‐over study comparing full dose cough responses with inhaled capsaicin in mild allergic asthmatics after 1 month of treatment with DSM‐17938 compared with matched placebo. Randomization and allocation to trial group were carried out by a central computer system. Histamine skin prick testing, airway hyper‐responsiveness and inflammatory cells in induced sputum were measured at every visit. Blood was collected to extract PBMCs and stimulated with CD3/CD28 to ascertain the effects of DSM‐17938 /placebo on T‐cell cytokine responses. Results Seventeen subjects were recruited and 15 completed the study (8 females, mean age 27.3 years). There was no difference in the change in maximum capsaicin‐evoked coughs (Emax) after treatment with L . reuteri DSM‐17938 compared with placebo [mean difference 2.07 coughs (95% CI −2.77 to 6.91, p = .38) or relative changes in geometric mean ratios for the dose evoking at least half the Emax (ED50) [1.05 (95% CI 0.31–3.58, p = .94)], concentration evoking 2 coughs (C2) [0.63 (0.26–1.53), p = .28] and 5 coughs (C5) [0.79 (0.25–2.50), p = .67]. There was no effect on histamine skin prick wheal size, intensity of itch sensation, methacholine PC20, airway inflammation or T‐cell responses after stimulation with CD3/CD28. There were no serious adverse events. One subject developed a mild upper respiratory tract infection and another mild transient nausea whilst on DSM‐17938. Conclusion In this small study in adults with mild allergic asthma, we found no evidence that L . reuteri DSM‐17938 has any systemic effects on airway nerves, smooth muscle, sputum inflammatory cells, skin responses or T‐cell responses after oral consumption. Trial Registration Clinicaltrials.gov Identifier: NCT03603522.