what amount of venlafaxine has been prescribed to patient 49140 for the first time until 12 months ago?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 49140 ) and prescriptions.drug = 'venlafaxine' and datetime(prescriptions.startdate) <= datetime(current_time,'-12 month') order by prescriptions.startdate asc limit 1