what was the bupivacaine 0.1% dose that patient 64136 was last prescribed in 09/2102?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 64136 ) and prescriptions.drug = 'bupivacaine 0.1%' and strftime('%y-%m',prescriptions.startdate) = '2102-09' order by prescriptions.startdate desc limit 1