when did patient 7524 get a norepinephrine bitartrate prescription for the last time until 06/2105?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 7524 ) and prescriptions.drug = 'norepinephrine bitartrate' and strftime('%y-%m',prescriptions.startdate) <= '2105-06' order by prescriptions.startdate desc limit 1