Which of the following is a typical appearance of intermediate-acting insulin?

• A. Clear
• B. Colorless
• C. Opaque
• D. Cloudy

Answer: (D)

Insulin formulations differ in appearance based on whether they’re a clear solution or a suspension. Intermediate-acting insulin is a suspension of insulin crystals with additives like protamine and zinc, which gives it a cloudy, milky look. Because it’s a suspension, you roll or gently invert the vial to resuspend the crystals before drawing up a dose, rather than shaking it. Rapid-acting and regular insulins are clear solutions, and long-acting insulins are also clear. So the typical appearance of intermediate-acting insulin is cloudy.