The study has been approved by the Western Norway Regional Committee for Medical and Health Research Ethics (REKVEST 2014/1885) and by the Norwegian Medicines Agency; European Union Drug Regulating Authorities Clinical Trials (EUDRACT) No. 2014-000302-34 (enclosed). The study will be performed under the guidance of the Paediatric Clinical Trial Unit at Haukeland University Hospital, a unit that has extensive experience in running clinical trials in children.