how many total doses of syringe (iv room) was prescribed to patient 77980 until 50 months ago?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 77980 ) and prescriptions.drug = 'syringe (iv room)' and datetime(prescriptions.startdate) <= datetime(current_time,'-50 month')