until 28 months ago, what was the first drug patient 27172 was prescribed via the iv drip route?
select prescriptions.drug from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 27172 ) and prescriptions.route = 'iv drip' and datetime(prescriptions.startdate) <= datetime(current_time,'-28 month') order by prescriptions.startdate asc limit 1