Patients/parents/legal guardians will be advised that rescue medication will be available immediately on request at any time during or after the completion of the treatment. The rescue medication to be used will be at the discretion of the blinded clinician. The rescue medication is dependent on the standard practice at the participating site. For the purpose of being all inclusive, rescue analgesia will be intranasal fentanyl, intranasal diamorphine, intravenous morphine or oral morphine