instruction: how many patients have the procedure icd9 code 8968 and have been prescribed base drug type?
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 = "8968" AND prescriptions.drug_type = "BASE"