what is the total dosage of chlorhexidine gluconate 0.12% oral rinse that patient 57050 has been prescribed in this month?
select sum(prescriptions.dose_val_rx) from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 57050 ) and prescriptions.drug = 'chlorhexidine gluconate 0.12% oral rinse' and datetime(prescriptions.startdate,'start of month') = datetime(current_time,'start of month','-0 month')