what was the drug that was prescribed to patient 66411 via the os route on the first hospital visit for the first time?
select prescriptions.drug from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 66411 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and prescriptions.route = 'os' order by prescriptions.startdate asc limit 1