what was the name of the medication which was prescribed to patient 14990 the last time since 180 months ago?
select prescriptions.drug from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 14990 ) and datetime(prescriptions.startdate) >= datetime(current_time,'-180 month') order by prescriptions.startdate desc limit 1