Understanding insulin

Disclaimer: This information is for educational purposes only and should not replace medical advice. Always follow your healthcare provider’s instructions regarding insulin therapy.

Insulin therapy is a cornerstone of diabetes management, helping maintain stable blood glucose levels. Understanding the characteristics of different types of insulin—including their onset, peak, duration, and mixing guidelines—is essential for safe and effective use.

Key Terms

• Onset: How quickly the insulin begins to lower blood glucose after injection.
• Peak: The time period when insulin is at its maximum strength, having the greatest glucose-lowering effect.
• Duration: How long the insulin continues to have any glucose-lowering activity.

Types of Insulin

Rapid-Acting Insulins

Examples: Insulin lispro (Humalog), insulin aspart (NovoLog), insulin glulisine (Apidra)

• Onset: Approximately 10–20 minutes after injection
• Peak: About 1–3 hours
• Duration: 3–5 hours
• Use: Taken just before or with a meal to manage postprandial (after-meal) blood sugar spikes.

Short-Acting (Regular) Insulin

Examples: Humulin R, Novolin R

• Onset: 30 minutes to 1 hour
• Peak: 2–4 hours
• Duration: 5–8 hours
• Use: Often taken about 30 minutes before a meal. May be used in combination with intermediate or long-acting insulins.

Intermediate-Acting Insulin (NPH)

Examples: Humulin N, Novolin N

• Onset: 1–2 hours
• Peak: 4–8 hours
• Duration: 10–18 hours
• Use: Provides basal insulin coverage for about half a day or overnight. Often taken twice daily. May be mixed with short or rapid-acting insulins in the same syringe (if guidelines allow).

Long-Acting Insulins

Examples: Insulin glargine (Lantus, Basaglar), insulin detemir (Levemir), insulin degludec (Tresiba)

• Onset: About 1–2 hours (glargine, detemir), 1 hour (degludec)
• Peak: No pronounced peak; relatively steady action.
• Duration:
  • Glargine (Lantus, Basaglar): ~24 hours
  • Detemir (Levemir): ~12–24 hours (dose-dependent)
  • Degludec (Tresiba): ~42 hours
• Use: Provides a consistent “basal” level of insulin throughout the day and night. Typically taken once daily (sometimes twice with detemir). Not usually mixed with other insulins in the same syringe.

Premixed Insulins

Examples: 70/30 (NPH/Regular), 75/25 (NPL/Lispro), 70/30 (Aspart Protamine/Aspart)

• Onset, Peak, Duration: Vary depending on proportions. Usually the onset and peak reflect the shorter-acting component, while the duration is influenced by the intermediate component.
• Use: Simplify regimens by combining basal and bolus insulins in one injection. Typically taken before meals.

Mixing Guidelines

• Which Insulins Can Be Mixed?
  Typically, only NPH (intermediate-acting, cloudy) can be mixed with a short- or rapid-acting insulin (clear) in the same syringe. Long-acting insulins such as glargine, detemir, or degludec must NOT be mixed with other types of insulin.
• Mixing Order (Cloudy and Clear):
  • Always draw up the clear (rapid-acting or regular) insulin first, then the cloudy (NPH) insulin.
  • The common mnemonic is “Clear before Cloudy.” This prevents contamination of the rapid/short-acting vial with NPH.
• Procedure for Mixing:
  1. Wash hands and gather supplies.
  2. Roll the NPH insulin vial gently between your palms to mix the suspension (do not shake vigorously).
  3. Inject air into the NPH (cloudy) vial first, then inject air into the regular or rapid-acting (clear) vial.
  4. Draw up the required dose of the clear insulin.
  5. Draw up the required dose of the cloudy (NPH) insulin into the same syringe.
  Make sure to confirm total units drawn and avoid introducing air bubbles.

Additional Tips

• Storage:
  Keep unopened insulin vials or pens in the refrigerator. Once opened, many can be stored at room temperature for a specified number of days (check the manufacturer’s instructions).
• Appearance Check:
  Rapid-acting, short-acting, and long-acting insulins are typically clear. NPH (intermediate-acting) insulin and insulin mixtures often appear cloudy. Do not use insulin that has clumps, frosting, or particles.
• Timing and Meal Planning:
  Understanding onset and peak times helps in timing insulin doses with meals or snacks to best control post-meal blood glucose levels.
• Monitoring and Adjusting:
  Blood glucose monitoring is essential. Your healthcare provider may adjust your insulin type, dose, and timing based on your glucose readings, lifestyle, and dietary patterns.

In Summary:
Each type of insulin differs in how quickly it starts working, when it peaks, and how long it lasts. Proper mixing (when applicable) and timing around meals are crucial for optimal blood glucose control. By understanding these differences, patients can work more effectively with their healthcare team to achieve their diabetes management goals.

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