instruction: when was the last time that patient 1902 was prescribed a medication via iv during the current hospital visit?
response: SELECT prescriptions.startdate FROM prescriptions WHERE prescriptions.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 1902 AND admissions.dischtime IS NULL) AND prescriptions.route = 'iv' ORDER BY prescriptions.startdate DESC LIMIT 1