instruction: what's the last prescription time for vancomycin hcl for patient 5364 in the first hospital encounter?
response: SELECT prescriptions.startdate FROM prescriptions WHERE prescriptions.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 5364 AND NOT admissions.dischtime IS NULL ORDER BY admissions.admittime LIMIT 1) AND prescriptions.drug = 'vancomycin hcl' ORDER BY prescriptions.startdate DESC LIMIT 1