Mepolizumab for the Treatment of Chronic Cough With Eosinophilic Airways Diseases

Inclusion Criteria: 1. Aged ≥18 2. Subjects with a history of chronic cough (cough lasting for \>8 weeks) 3. Evidence of airway eosinophilia (sputum eosinophilia\>2%) 4. Forced expiratory volume-1 ≥ 70% of predicted 5. Normal chest x-ray (within the last 6 months) 6. At least one dose of a COVID-19 vaccine a minimum of 2 weeks prior to enrollment Exclusion Criteria: 1. Symptoms of upper respiratory tract infection in the last 1 month which have not resolved. 2. Lower respiratory tract infection or pneumonia in the last 1 month. 3. Subjects with a positive covid-19 test within 2 weeks of screening 4. Subjects with seasonal allergic rhinitis that affects their asthma control 5. Current smoker or ex-smoker with ≥10 pack year smoking history and abstinence of ≤6 months 6. Symptoms of uncontrolled asthma at screening defined as: Asthma Control Questionnaire-5 \>1.5, or use of 3 or more puffs of a short acting beta-2 agonist per week, or an exacerbation in the previous month requiring oral prednisone or antibiotics. 7. Use of regular maintenance oral corticosteroids or long-acting muscarinic antagonist within 4 weeks prior to enrolment into the study. 8. A previous asthma exacerbation requiring Intensive Care Unit admission. 9. Significant other primary pulmonary disorders in particular; pulmonary embolism, pulmonary hypertension, interstitial lung disease, lung cancer, cystic fibrosis, emphysema or bronchiectasis. 10. Any history or symptoms of cardiovascular disease, particularly coronary artery disease, arrhythmias, hypertension, or congestive heart failure. 11. Any history or symptoms of significant neurologic disease, including transient ischemic attack, stroke, seizure disorder, or behavioural disturbances 12. Uncontrolled diabetes 13. End-stage kidney or liver disease 14. Clinically significant abnormalities in laboratory test results during the screening period (including complete blood count, coagulation, electrolytes, liver function tests) unless deemed not significant by the investigator. 15. Any history or symptoms of clinically significant autoimmune disease 16. History of anaphylaxis to any biologic therapy or vaccine 17. History of Guillain-Barre Syndrome 18. A helminth parasitic infection diagnosed within 24 weeks prior to the date of informed consent is obtained that has not been treated with or has failed to respond to standard of care therapy. 19. Positive hepatitis B surface antigen, or hepatitis C virus antibody serology, or a positive medical history for hepatitis B or C. Subjects with a history of hepatitis B vaccination without history of hepatitis B can enroll. 20. A history of immunodeficiency disorders including a positive human immunodeficiency virus test 21. Pregnancy or breast-feeding. 22. Women of childbearing potential must not be actively seeking pregnancy, and must use an effective form of birth control (confirmed by the Investigator). Effective forms of birth control include: true sexual abstinence, a vasectomized sexual partner, Implanon, female sterilization by tubal occlusion, any effective intrauterine device/ intrauterine system levonorgestrel Intrauterine system, Depo-Provera™ injections, oral contraceptive, and Evra Patch™ or Nuvaring™. Women of childbearing potential must agree to use an effective method of birth control, as defined above, from enrolment, throughout the study duration and within the 8 treatment weeks. They must demonstrate a negative serum pregnancy test at screening and demonstrate a negative urine pregnancy test immediately before each dose of study drug or placebo. Women not of childbearing potential are defined as women who are either permanently sterilized (hysterectomy, bilateral oophorectomy, or bilateral salpingectomy), or who are postmenopausal. Women will be considered postmenopausal if they have been amenorrheic for 12 months prior to the planned date of randomization without an alternative medical cause. The following age-specific requirements apply: i. Women \<50 years old would be considered postmenopausal if they have been amenorrheic for 12 months or more following cessation of exogenous hormonal treatment and follicle stimulating hormone (FSH) levels in the postmenopausal range. ii. Women ≥50 years old would be considered postmenopausal if they have been amenorrheic for 12 months or more following cessation of all exogenous hormonal treatment. 23. Male patients not using an acceptable method of contraception. All male patients who are sexually active must agree to use an acceptable method of contraception (condom with or without spermicide, vasectomy) from the first dose of study drug until their last dose. 24. Use of angiotensin-converting-enzyme inhibitors 25. Use of immunosuppressive medication (including but not limited to: methotrexate, cyclosporine, azathioprine, intramuscular long-acting depot corticosteroid, oral corticosteroid, or any experimental anti-inflammatory therapy) within 3 months prior to the date informed consent is obtained 26. Use of any other biological within 4 months or 5 half-lives prior to randomization, whichever is longer. 27. Any centrally acting medication within the last 2 weeks which in the view of the investigator could influence the coughing (Any participant who is taking amitriptyline, dextromethorphan, pregabalin, gabapentin or opioids will not be eligible to take part in this study unless they are willing and medically able to withdraw from such medication for the duration of the study. The reason for this is that centrally acting medications may influence coughing rates.) 28. History of psychiatric illness, drug or alcohol abuse which may interfere in the participation of the trial.