The aim of this study is to evaluate the efficacy and safety of Elixirium thymi compositum (Formulae Normales (FoNo) VIII.) compared to a placebo in children between 6 and 17 years old to treat their acute bronchitis. The main question it aims to answer is: Is Elixirium thymi compositum (FoNo VIII.) safe and effective in the treatment of acute bronchitis compared to placebo?

Acute bronchitis is a common disease caused mainly by viral infections. Although there is a standard symptomatic therapy for it, antibiotics are often prescribed, which contributes to an increase in antibiotic resistance. Elixirium thymi compositum (FoNo VIII.) might be an alternative therapeutic option.

The aim is to establish the role of this product by evaluating its clinical efficacy and safety, meanwhile reducing the misuse of antibiotics in treating this condition.

This is a randomized, controlled, double-blinded, two-arm multicenter phase 4 trial. Eligible patients will be pediatric individuals between 6 and 17 years old diagnosed with acute bronchitis. The trial will enroll at least 56 eligible participants with a Total Bronchitis Severity Score (BSS) ranging from 5 to 12 points. Participants will be assigned randomly in a 1:1 ratio to receive either Elixirium thymi compositum at an age-dependent dosage (18-30 ml daily) for 5 days or a placebo with the same concentration and duration.

The trial's primary endpoint is the assessment of symptom improvement in acute bronchitis, as indicated by changes in the BSS score on Day 7. Secondary endpoints include evaluating use of concomitant medications and dietary supplements, safety and tolerability through reported adverse events, and the necessity of antibiotic usage. These secondary endpoints will provide deeper insights into the differences between the treatment and placebo groups. The primary and secondary endpoints will be monitored throughout a follow-up period of 7 days.

Inclusion Criteria:

1. age 6-17 years,
2. diagnosis of acute bronchitis and the Total Bronchitis Severity Score of the patient is between 5-12 points,
3. informed consent form and patient information leaflet signed by the patient and the parent or legal guardian, and
4. no pregnancy, no planned pregnancy, and no breastfeeding.

Exclusion Criteria:

1. allergy to the active ingredients or any other components of Elixirium thymi compositum,
2. hypersensitivity to plants of the Lamiaceae family,
3. chronic respiratory diseases such as asthma, chronic bronchitis, and chronic obstructive pulmonary disease,
4. pneumonia in the last year,
5. a history of recurrent or severe laryngotracheal stenosis due to inflammation,.
6. active or chronic inflammatory bowel disease (e.g., Crohn's disease, ulcerative colitis) or infectious enterocolitis,
7. heart failure (New York Heart Association Class II-IV),
8. smoking (the patient currently smokes or has smoked at least one cigarette, cigar, or pipe daily),
9. a diagnosis or history of lung cancer,
10. a history of lung or chest surgery,
11. epilepsy,
12. any viral infection in the last 6-8 weeks,
13. immunostimulant medications, antibiotics, or systemic steroid treatments in the past month,
14. antihistamines, expectorants, or local steroids applied in the last two weeks,
15. hereditary fructose intolerance, glucose-galactose malabsorption, or sucrase-isomaltase deficiency,
16. taking or planning to take hormonal contraceptives within the next 2 weeks
17. chronic liver disease (e.g., cirrhosis) or acute hepatitis.

There is not a plan to make individual participant data (IPD) available for this study. The informed consent form, in compliance with the EU General Data Protection Regulation (GDPR) and relevant Hungarian laws, specifically informs participants that their data will be handled confidentially, stored anonymously, and presented only in aggregate, anonymized form in any resulting publications. The consent does not include permission for broader sharing of individual-level data outside the study team or approved data processors.