A 35-year-old type 1 diabetic, weighing 80 kg, on isophane insulin 100 units/mL in 3 mL pens, daily dose 0.9 units/kg. How many pens are needed for 30 days?

A 35-year-old type 1 diabetic, weighing 80 kg, on isophane insulin 100 units/mL in 3 mL pens, daily dose 0.9 units/kg. How many pens are needed for 30 days?

• A. 6 pens
• B. 7 pens
• C. 8 pens
• D. 9 pens

Answer: (C)

Convert the dose from weight-based to daily units, then scale up to a month and divide by the insulin in each pen. Daily dose = 0.9 units/kg × 80 kg = 72 units per day. Over 30 days: 72 × 30 = 2160 units needed. Each pen contains 3 mL × 100 units/mL = 300 units. Pens required = 2160 ÷ 300 = 7.2, so you round up to a full pen, giving eight pens. Seven pens would provide 2100 units (not enough), while eight pens provide 2400 units (sufficient).

Convert the dose from weight-based to daily units, then scale up to a month and divide by the insulin in each pen.

Daily dose = 0.9 units/kg × 80 kg = 72 units per day. Over 30 days: 72 × 30 = 2160 units needed. Each pen contains 3 mL × 100 units/mL = 300 units. Pens required = 2160 ÷ 300 = 7.2, so you round up to a full pen, giving eight pens. Seven pens would provide 2100 units (not enough), while eight pens provide 2400 units (sufficient).