what is the dose of neo*iv*gentamicin that is first prescribed to patient 59707?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 59707 ) and prescriptions.drug = 'neo*iv*gentamicin' order by prescriptions.startdate asc limit 1