when was patient 18757 prescribed medication via ih route, for the last time until 02/2105?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 18757 ) and prescriptions.route = 'ih' and strftime('%y-%m',prescriptions.startdate) <= '2105-02' order by prescriptions.startdate desc limit 1