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Felix Ratjen

Title: Paediatric Respirologist, Division of Respiratory Medicine
Designations: MD, PhD, FRCP(C), FERS
Pronouns: he/him
Phone: 416-813-6167
Fax: 416-813-6246
Alternate Contact Name: Anna Odina
Alternate Phone: 416-813-7654 ext. 409192, Clinic: 416-813-5826
Alternate Email:
Alternate Fax: (Clinic) 416-813-5821
U of T Positions: Professor, Department of Paediatrics

Research Positions

Program Head and Senior Scientist
Translational Medicine


Dr. Felix Ratjen is a Paediatric Respirologist in the Division of Respiratory Medicine at The Hospital for Sick Children (SickKids) and Professor of Paediatrics at the University of Toronto. He is also Program Head and Senior Scientist in the Translational Medicine research program at SickKids Research Institute. He is co-leading the Cystic Fibrosis (CF) Centre at SickKids with Christine Bear, another Senior Scientist in the Molecular Medicine Program.

Dr. Ratjen completed a majority of his medical education in Germany, along with a research fellowship at the Children's Hospital in Boston. He subsequently worked at the University of Essen, where he was appointed Deputy Chief of the Department of Paediatrics in 1998 and Professor of Paediatrics in 2001. Until 2005 he was the chief executive of the scientific board of the German CF Foundation before relocating in Canada in the same year. From 2005 to 2022, he was appointed Division Chief of Respiratory Medicine at SickKids. He is also involved in the organizing committees of major respiratory meetings (American Thoracic Society, European Respiratory Society and the North American CF conference), works on multiple grant review panels and is a member of several editorial boards, including the American Journal of Respiratory and Critical Care Medicine, Thorax, Pediatric Pulmonology Lancet Respiratory Medicine and the Journal of Cystic Fibrosis.


Dr. Ratjen is conducting multiple clinical trials addressing cystic fibrosis lung disease, including new therapeutic strategies to target the underlying defect, treatment of airway infections such as first infection with Pseudomonas aeruginosa, airway inflammation and other important aspects of the disease. While some of these studies are single centre studies within the CF Centre at SickKids or in collaboration with the adult centre at St. Michael’s Hospital, many of them include both national and international collaborations with centres in Canada, the U.S., Europe and Australia. In addition, he is involved in developing and validating new outcome measures to quantify important aspects of CF lung disease that can be utilized in clinical trials. He also studies other lung diseases, including Hereditary Hemorrhagic Telangiectasia (HHT), for which he is leading one of the largest dedicated paediatric clinics.

Education and experience

  • 2009: Leadership Training, University of Toronto, Rotman School of Business
  • 1996: PhD, Habilitation Paediatrics, University of Essen, Germany
  • 1988–1993: Paediatric training, Children’s Hospital, University of Essen
  • 1987–1989: Research Fellowship, Pediatric Pulmonary Medicine, Children's Hospital, Harvard Medical School, Boston, Massachusetts
  • 1986: Doctor of Medicine, Johann Wolfgang Goethe University in Frankfurt a.M, Germany


  • 2018: Maestro de Pulmonologica Pediatricia Latinamericana
  • 2014: Fellowship of the ERS (FERS)
  • 2012: Queen Elizabeth II Diamond Jubilee Medal for service to Cystic Fibrosis Patients
  • 2005–2020: SickKids Foundation, H.E Sellers Chairholder
  • 2005: Adolft-Windorfer Prize for Outstanding Research in CF

Associate Editor

  • Journal of Cystic Fibrosis
  • Canadian Journal Respiratory and Critical Care Medicine
  • Cochrane: CF and Rare Disease Group
  • Canadian Respiratory Journal

Editorial Boards

  • American Journal of Respiratory and Critical Care Medicine
  • Lancet Respiratory Medicine
  • Pediatric Pulmonology
  • Thorax


  1. Efficacy and safety of lumacaftor and ivacaftor in patients aged 6-11 years with cystic fibrosis homozygous for F508del-CFTR: a randomised, placebo-controlled phase 3 trial. Ratjen F, Hug C, Marigowda G, Tian S, Huang X, Stanojevic S, Milla CE, Robinson PD, Waltz D, Davies JC; VX14-809-109 investigator group.Lancet Respir Med. 2017 Jul;5(7):557-567. 
  2. Hyperpolarised 129Xe magnetic resonance imaging to monitor treatment response in children with cystic fibrosis. Rayment JH, Couch MJ, McDonald N, Kanhere N, Manson D, Santyr G, Ratjen F.Eur Respir J. 2019 May 2;53(5):1802188.
  3. Changes in Lung Clearance Index in Preschool-aged Patients with Cystic Fibrosis Treated with Ivacaftor (GOAL): A Clinical Trial. Ratjen F, Klingel M, Black P, Powers MR, Grasemann H, Solomon M, Sagel SD, Donaldson SH, Rowe SM, Rosenfeld M.Am J Respir Crit Care Med. 2018 Aug 15;198(4):526-528. 
  4. Inhaled hypertonic saline in preschool children with cystic fibrosis (SHIP): a multicentre, randomised, double-blind, placebo-controlled trial. Ratjen F, Davis SD, Stanojevic S, Kronmal RA, Hinckley Stukovsky KD, Jorgensen N, Rosenfeld M; SHIP Study Group. Lancet Respir Med. 2019 Sep;7(9):802-809. doi: 10.1016/S2213-2600(19)30187-0. Epub 2019 Jun
  5. The future of cystic fibrosis care: a global perspective. Bell SC, Mall MA, Gutierrez H, Macek M, Madge S, Davies JC, Burgel PR, Tullis E, Castaños C, Castellani C, Byrnes CA, Cathcart F, Chotirmall SH, Cosgriff R, Eichler I, Fajac I, Goss CH, Drevinek P, Farrell PM, Gravelle AM, Havermans T, Mayer-Hamblett N, Kashirskaya N, Kerem E, Mathew JL, McKone EF, Naehrlich L, Nasr SZ, Oates GR, O'Neill C, Pypops U, Raraigh KS, Rowe SM, Southern KW, Sivam S, Stephenson AL, Zampoli M, Ratjen F.  Lancet Respir Med. 2020 Jan;8(1):65-124. 

  • 2022–2025: Inflammatory and Immune Biomarkers of Response to Elexacaftor/Tezacaftor/Ivacaftor in People with CF, Co-Principal Investigator, Cystic Fibrosis Canada, $295,100 CAD.
  • 2022–2024: Multi-site collaboration to validate use of patient-derived nasal cultures for expanding access to CFTR Modulators, Co-Investigator, Cystic Fibrosis Canada, $200,000 CAD
  • 2021–2023: LITE study, Principal Investigator, Cystic Fibrosis Foundation, $87,539 CAD.
  • 2020–2025: Magnetic Resonance Imaging Toolbox Lung Structure and Function in the Early Years of Life, Co-Investigator, Canadian Institutes of Health Research, $164,088 CAD.
  • 2020–2024: PROMISE study, Co-Principal Investigator (Paediatric Substudy), $5,000,000 USD (total).
  • 2020–2023: North American Multiple Breath Washout Center, Principal Investigator, $438,215 USD.
  • 2018–2024: Personalized Therapy for Individuals with Cystic Fibrosis, Principal Investigator, Genome Canada – LSARP, $10,073,757 CAD ($5,000,000 GC contribution).
  • 2015–2024: Program for Individualized CF Therapy, Co-Principal Investigator, SickKids Foundation – Cystic Fibrosis Canada, $7,500,000 CAD.

Relevant pages

Ratjen Lab

The Ratjen Lab's research focuses on evaluating novel treatments, designing new ways to conduct research and investigating how we can better measure and monitor lung function in young children.

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