instruction: when is the last time patient 002-13510 was prescribed medication via po in the first hospital visit?
response: SELECT 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 = '002-13510' AND NOT patient.hospitaldischargetime IS NULL ORDER BY patient.hospitaladmittime LIMIT 1)) AND medication.routeadmin = 'po' ORDER BY medication.drugstarttime DESC LIMIT 1