when was patient 77177 first prescribed the medication via the ou route in the first hospital encounter?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 77177 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and prescriptions.route = 'ou' order by prescriptions.startdate asc limit 1