during this year, how many patients were prescribed sodium citrate/citric acid?
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select prescriptions.hadm_id from prescriptions where prescriptions.drug = 'sodium citrate/citric acid' and datetime(prescriptions.startdate,'start of year') = datetime(current_time,'start of year','-0 year') )