Some insulin pens are designed to be used with an insulin cartridge. These pens are meant to be reused. Insulin pens that do not come with separate insulin cartridges are disposable, and the insulin is pre-filled inside the pen. When you prepare to take insulin, check the label on the bottle (vial) or cartridge for the:

• Expiration date of the insulin.
• Correct name and source of insulin (human or pig) prescribed for you.
• Correct type of insulin prescribed for you (rapid-, short-, intermediate-, or long-acting, or mixed).
• Correct concentration of insulin prescribed for you. (The most commonly used concentration is U-100, which contains 100 units of insulin per millilitre or cubic centimetre.) Sometimes insulin is produced in a less concentrated (diluted) form for babies. Make sure you give your baby the dilution your doctor prescribed.

Also, check the bottle or cartridge for cracks or chips. Look for changes in the appearance of the insulin that can indicate it will not work, such as:

• A coating of white crystals on the inside surface of the bottle.
• A grainy look or clumping or curdling of the insulin.
• Other changes in the insulin's clarity or colour.