when was the last time that patient 47460 was prescribed medication during the last hospital encounter via iv route?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 47460 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and prescriptions.route = 'iv' order by prescriptions.startdate desc limit 1