how many hours has passed since the last time on their current hospital visit that patient 42473 was prescribed buprenorphine?
select 24 * ( strftime('%j',current_time) - strftime('%j',prescriptions.startdate) ) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 42473 and admissions.dischtime is null ) and prescriptions.drug = 'buprenorphine' order by prescriptions.startdate desc limit 1