Â¾ The vial can be used for more than one dose because it contains a preservative called benzyl alcohol to keep it clean (sterile) between uses. Â¾ Check with your pharmacist to ensure that the strength of methotrexate is 50 mg/2 mL and that it contains the preservative. Â¾ The vial comes with a coloured protective cap that indicates the vial is new. This cap is removed before use and does not re-attach.