OBJECTIVES Minimizing waste of the use of drugs allows optimization of available resources in a scarce environment. Grouping patients may be an alternative to reduce drug waste in oncology. The aim of this study is to evaluate the economic impact of streamlined form of dispensation and percentage of drug wastage of the total drug expenditure in supplementary health system. METHODS Patients receiving antineoplasic treatment for stomach, colon, rectosigmoid, rectum, lung and breast cancer were eligible and selected retrospectively from the private market administrative claims database (Evidencias database). Name and any other personal identification were not available at the database. Prescription and date of administration were collected from 3 selected private institutions considering large to small size in terms of patients. Waste of drug was calculated and it was defined as unavoidable or inappropriate clearance of partially drug use.  All analyses were performed according to regimen and disease.  Saving costs were calculated assuming minimization of waste by optimizing fully drug among group patients. Costs were derived from Simpro table. Exchange rate used was 1.00USD = 2.20BRL. RESULTS Seventeen drugs were identified among reported chemotherapy regimens in which 11 were analyzed due to potential of saving costs. From these, only 6 drugs could be rationalized. The optimization of drug dispensing would lead to a year savings of US$ 83.587,88, US$ 17.592,22 and US$ 8.225,24 to a large, medium and small clinic, respectively.Calculated drug wastage represented from 2% to 8% of the total drug expenditure, regarding on the antineoplastic used. Five of the 11 drugs did not cause savings due to small number of patients receiving those treatments.  CONCLUSIONS Grouping patients for  drug wastage minimization is an effective way to reduce costs. Furthermore, savings can be increased by gathering patients of different diseases.