instruction: What is the total number of patients who were treated with drug code levo750 and had clinical chemistry tests?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id INNER JOIN lab ON demographic.hadm_id = lab.hadm_id WHERE prescriptions.formulary_drug_cd = "LEVO750" AND lab."CATEGORY" = "Chemistry"