what was the last time patient 5866 was prescribed senna and syringe (0.9% sodium chloride) until 19 months ago, 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 = 'senna' and admissions.subject_id = 5866 and datetime(prescriptions.startdate) <= datetime(current_time,'-19 month') ) as t1 join ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'syringe (0.9% sodium chloride)' and admissions.subject_id = 5866 and datetime(prescriptions.startdate) <= datetime(current_time,'-19 month') ) as t2 on t1.subject_id = t2.subject_id where datetime(t1.startdate) = datetime(t2.startdate) order by t1.startdate desc limit 1