when they visited the hospital first time, when was patient 32592 prescribed a medication via pb route for the first time?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 32592 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and prescriptions.route = 'pb' order by prescriptions.startdate asc limit 1