To quickly calculate the number of vials necessary for a 90-day supply of insulin, take the total daily dose (TDD) and divide by 10. For example, if a patient is taking isophane insulin 30 units b.i.d., the TDD is 60 units per day; 60 divided by 10 is six. Therefore, six vials are needed to cover the patient’s basal needs for the 90-day period. Remember, opened insulin vials should be thrown out after 28 days.
—LEE ERBE, NP-BC, and JEREMY SOULE, MD, Charleston, S.C. (119-27)