what was the first dose of pantoprazole until 15 months ago, prescribed to patient 31169?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 31169 ) and prescriptions.drug = 'pantoprazole' and datetime(prescriptions.startdate) <= datetime(current_time,'-15 month') order by prescriptions.startdate asc limit 1