instruction: count the number of patients who had been prescribed an heparin flush hickman (100 units/ml) since 2101.
response: SELECT COUNT(DISTINCT admissions.subject_id) FROM admissions WHERE admissions.hadm_id IN (SELECT prescriptions.hadm_id FROM prescriptions WHERE prescriptions.drug = 'heparin flush hickman (100 units/ml)' AND STRFTIME('%y', prescriptions.startdate) >= '2101')