what was the name of the medication patient 26398 was prescribed the first time a month before?
select prescriptions.drug from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 26398 ) and datetime(prescriptions.startdate,'start of month') = datetime(current_time,'start of month','-1 month') order by prescriptions.startdate asc limit 1