when did patient 81461 receive the last prescription in their current hospital visit for vecuronium bromide?
select prescriptions.startdate from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 81461 and admissions.dischtime is null ) and prescriptions.drug = 'vecuronium bromide' order by prescriptions.startdate desc limit 1