when was the first time isotonic sodium chloride was prescribed to patient 3125 in this hospital visit?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 3125 and admissions.dischtime is null ) and prescriptions.drug = 'isotonic sodium chloride' order by prescriptions.startdate asc limit 1