how much neo*iv*gentamicin is prescribed the last time the previous month to patient 40435?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 40435 ) and prescriptions.drug = 'neo*iv*gentamicin' and datetime(prescriptions.startdate,'start of month') = datetime(current_time,'start of month','-1 month') order by prescriptions.startdate desc limit 1