Magnesium spray for refractory or unexplained chronic cough in adults

Inclusion Criteria:

1. Males and females between 18 and 80 years.
2. Capable of giving signed informed consent.
3. Diagnosed with RCC (including unexplained chronic cough) for at least 6 months.
4. At least 8 coughs per hour, 24-hour cough frequency during the 14-day Run-In Period.
5. Score ≥ 40 mm on cough severity VAS at Screening.
6. Normal FEV1/FVC ratio of greater than 70% at Screening
7. A negative test for COVID-19.
8. Women of child-bearing potential and men must agree to use a highly effective contraception method during the study and for at least 14 days after the last dose.
9. Willing to carry study-related equipment as required for the study (e.g. cough monitor, phone).

Exclusion Criteria:

1. Current smoker/vaper (all forms of smoking and inhaled substances, including cannabis/tobacco smoke and nicotine vapours) or individuals who have given up smoking within the past 6 months, or those with \>20 pack-year smoking history.
2. Diagnosis of Chronic Obstructive Pulmonary Disease (COPD), bronchiectasis, idiopathic pulmonary fibrosis, uncontrolled asthma or other serious pulmonary disease.
3. Respiratory tract infection within 4 weeks before screening.
4. History of malignancy in the last 5 years, unless it is a non-serious skin cancer.
5. History of moderate or severe alcohol or drug use disorder within the last 3 years.
6. Opioid use with in the 7 days prior to screening.
7. History of a positive serologic test for hepatitis B virus surface antigen, or hepatitis C virus.
8. Previous participation in a clinical trial in the last 30 days or 6-half half-lives of test drug activity.
9. Current participation in or completion of speech language therapy intervention therapy for chronic cough within 8 weeks prior to screening.
10. Use of Prohibited medications within 4 weeks prior to screening and at any time during the study: anti-tussive therapy, systemic corticosteroids, ACE inhibitors, opioids.
11. Gabapentin and pregabalin are prohibited unless they are being administered for treatment of a condition other than RCC and have been on a stable dose of that medication for at least 6 weeks prior to screening and plan to remain on that dose for the duration of the study.
12. Tricyclic antidepressants are prohibited unless they are being administered for treatment of a condition other than RCC and have been on a stable dose of that medication for at least 12 weeks prior to screening and plan to remain on that dose for the duration of the study.
13. Beta blockers are prohibited unless they are on a stable dose for at least 6 weeks prior to screening.
14. Use of dietary supplements containing magnesium for the duration of the study.
15. History of myocardial infarction or other cardiac disorders as follows:

    * History of any of the following within 6 months prior to screening, myocardial infarction, stroke or transient ischemic attack, coronary revascularization (PCI or CABG), or heart failure.
    * History of clinically significant arrhythmias, poorly controlled hypertension.
    * Any condition that, in the opinion of the investigator, places the participant at high risk for an acute cardiovascular event including but not limited to: angina symptomatic peripheral arterial disease, severe valvular heart disease, planned cardiovascular intervention or surgery during the study period, baseline QTc interval \>450 ms (men) or \>470 ms (women), or any clinically significant ECG abnormality as determined by the Investigator.
16. History of any clinically significant or psychiatric condition that, in the eyes of the Investigator or designee, would not be suitable for this study. Or if, in the eyes of the Investigator or designee may prove non-compliant to study procedures.
17. Spouses or other family members with a chronic cough in the household.
18. Living and working in an excessively loud workplace (e.g. building site).