since 148 months ago, when was the first time that patient 16549 was prescribed both sterile water and sw at the same time?
select t1.startdate from ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'sterile water' and admissions.subject_id = 16549 and datetime(prescriptions.startdate) >= datetime(current_time,'-148 month') ) as t1 join ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'sw' and admissions.subject_id = 16549 and datetime(prescriptions.startdate) >= datetime(current_time,'-148 month') ) as t2 on t1.subject_id = t2.subject_id where datetime(t1.startdate) = datetime(t2.startdate) order by t1.startdate asc limit 1