what was the drug that was prescribed to patient 11579 in their last hospital visit via the ir route for the first time?
select prescriptions.drug from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 11579 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and prescriptions.route = 'ir' order by prescriptions.startdate asc limit 1