instruction: how many days have passed since last ascorbic acid 500 mg tab was prescribed to patient 013-28507 in this hospital visit?
response: SELECT 1 * (STRFTIME('%j', CURRENT_TIME()) - STRFTIME('%j', medication.drugstarttime)) FROM medication WHERE medication.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '013-28507') AND patient.hospitaldischargetime IS NULL) AND medication.drugname = 'ascorbic acid 500 mg tab' ORDER BY medication.drugstarttime DESC LIMIT 1