what was the name of the drug prescribed to patient 22756, two times until 17 months ago?
select t1.drug from ( select prescriptions.drug, count( prescriptions.startdate ) as c1 from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 22756 ) and datetime(prescriptions.startdate) <= datetime(current_time,'-17 month') group by prescriptions.drug ) as t1 where t1.c1 = 2