what's the name of the drug that was first prescribed to patient 3229 in 12/2105?
select prescriptions.drug from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 3229 ) and strftime('%y-%m',prescriptions.startdate) = '2105-12' order by prescriptions.startdate asc limit 1