when was the first time a drug was prescribed to patient 61500 until 11/2105?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 61500 ) and strftime('%y-%m',prescriptions.startdate) <= '2105-11' order by prescriptions.startdate asc limit 1