how much phenytoin sodium was prescribed for the last time until 01/2101 to patient 62977?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 62977 ) and prescriptions.drug = 'phenytoin sodium' and strftime('%y-%m',prescriptions.startdate) <= '2101-01' order by prescriptions.startdate desc limit 1