instruction: give me the number of patients taking additive type drug prescription who have procedure icd9 code 4105.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN procedures ON demographic.hadm_id = procedures.hadm_id INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE procedures.icd9_code = "4105" AND prescriptions.drug_type = "ADDITIVE"