Efficacy and Safety of XC8, Film-coated Tablets, in Children With Acute Respiratory Viral Infections

Inclusion Criteria:

1. Patient signing the Informed Consent Form and parent/adoptive parent signing theParent/Adoptive Informed Consent Form.
2. Male and female children between the ages of 6 and 17 years 10 months inclusive at thetime of screening.
3. Clinical diagnosis of acute respiratory viral upper respiratory tract infection (J00-J06 according to ICD-10) or acute bronchitis (J20, J21 according to ICD-10).
4. Onset of disease symptoms no more than 3 days prior to screening.
5. Presence of dry non-productive cough in the patient.
6. Frequency of cough attacks ≥10 in the last 24 h before the screening visit andrandomization.
7. Cough frequency rated by the patient (for patients 13-17 years of age) orparent/adoptive parent (for patients 6-12 years of age) as 3-4 points on the "daytimecough" section and 2-4 points on the "nighttime cough" Daytime and nighttime coughscales.
8. Patient (for patients 13-17 years of age) or parent/adoptive parent (for patients 6-12years of age) assessment of cough severity on the digital rating scale as ≥4 points.
9. No indication for therapy due to BHSA infection at the time of inclusion in the study:negative rapid test for group A β-hemolytic streptococcus.
10. For patients 14-17 years of age inclusive, consent to use reliable contraceptivemethods throughout study participation and for 3 weeks after the end of the study. Reliable contraceptive methods are: sexual rest, condom use in combination with spermicide. Non-inclusion Criteria:
11. Known or suspected hypersensitivity to the active substance or any of the excipientsof the study drug/placebo.
12. Known or suspected hypersensitivity to acetylcysteine.
13. Lactose intolerance, lactase deficiency, glucose-galactose malabsorption.
14. Trauma (including open wounds in the oral cavity and erosive desquamous lesions of theoral mucosa) and/or burns of the oropharynx, scarlet fever, rubella, measles, epidemicmumps at the time of screening or within 3 months before screening.
15. Acute obstructive laryngitis or suspected obstructive laryngitis.
16. Presence of signs of laryngeal stenosis (stridor, dyspnea).
17. Exacerbation of chronic bronchitis.
18. Bronchial asthma, including history.
19. Tuberculosis in the anamnesis.
20. Emphysema of the lungs in the anamnesis.
21. Acute or chronic pneumonia or suspected pneumonia.
22. Condition after intubation.
23. Gastroesophageal reflux being the primary cause of cough (in the opinion of theinvestigating physician).
24. Allergic rhinitis being the primary cause of cough (in the opinion of thephysician-researcher).
25. Body temperature > 39.0 °C.
26. Positive laboratory test result for SARS-CoV-2 antigen using an immunochromatographicassay at the time of screening1.
27. Need for systemic antibiotic therapy and/or other drugs/procedures on the prohibitedtherapy/procedure list.
28. Use of analgesics or antipyretics within 12 h prior to screening.
29. Use of glucocorticosteroids, β-adrenoblockers, ACE inhibitors, theophyllinepreparations, expectorants, cough suppressants, anesthetics, anti-allergic drugs (leukotriene receptor antagonists, H1-histamine receptor blockers, sodium cromoglycatepreparations), antiviral drugs, immunosuppressants, systemic antibacterial agentswithin 7 days before screening.
30. A history of smoking.
31. History of renal or hepatic impairment.
32. History of oncologic diseases.
33. Serious cardiovascular disease at the time of screening or within 12 months prior toscreening, including: severe arrhythmias requiring treatment with antiarrhythmicdrugs, unstable angina pectoris, heart and coronary artery surgery, stroke.
34. Other severe, decompensated or unstable somatic diseases (any disease or conditionthat threatens the patient's life or worsens the patient's prognosis and makes itimpossible for the patient to participate in the clinical trial).
35. Unwillingness or inability of the patient/parent/adoptive parent to comply with theprotocol procedures (in the opinion of the investigating physician).
36. Pregnancy or breastfeeding period (for female patients).
37. Alcoholism, drug dependence, substance abuse history and/or at the time of screening.
38. A history of schizophrenia, schizoaffective disorder, bipolar disorder, or otherpsychiatric pathology.
39. Participation in another clinical trial within 3 months prior to inclusion in thestudy.
40. Other conditions that, in the opinion of the investigating physician, preclude thepatient's inclusion in the study.

Exclusion criteria:

1. Identification of a confirmed case of COVID-19.
2. Ineffectiveness of therapy - persistence or increase in cough attack frequency ≥1 byVisit 3 (Day 8-9) compared to Visit 1 (Day 1).
3. Adverse events (AEs) requiring withdrawal of study drug/placebo.
4. Occurrence of any disease or condition during the study that, in the opinion of theinvestigator, worsens the patient's prognosis and makes it impossible for the patientto continue participating in the clinical trial.
5. Erroneous inclusion of a patient who does not meet the inclusion criteria and/or meetsthe criteria for non-inclusion.
6. Taking any of the drugs of prohibited therapy, performing a prohibited procedure.
7. Need to prescribe a prohibited concomitant therapy/procedure.
8. Pregnancy of the patient.
9. Willingness of the patient and/or his/her parent/adoptive parent to terminate thepatient's participation in the study.
10. Lack of adequate cooperation of the patient and/or his/her parent/adoptive parent withthe physician-researcher during the research process.
11. Other protocol violations that in the opinion of the physician-researcher aresignificant.
12. Other administrative reasons.