how many days have passed since the last 0.83% sodium chloride prescribed during the current hospital encounter for patient 55281?
select 1 * ( strftime('%j',current_time) - strftime('%j',prescriptions.startdate) ) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 55281 and admissions.dischtime is null ) and prescriptions.drug = '0.83% sodium chloride' order by prescriptions.startdate desc limit 1