Insulin is a hormone that plays a fundamental role in managing blood sugar levels for individuals with diabetes. It helps glucose enter cells for energy. Insulin comes in various formulations, each designed to act differently.
While many insulin types are clear liquids, some are intentionally cloudy. This cloudiness is a normal characteristic for formulations designed to release insulin slowly over time. This article explores why some insulins are cloudy, identifies these types, and provides guidance on their proper handling and storage.
Understanding Insulin’s Appearance
The appearance of insulin is directly related to its chemical formulation and how it works. Clear insulins are solutions where the insulin protein is fully dissolved, often acting quickly or providing a steady, peakless release.
In contrast, cloudy insulins are suspensions, not true solutions. They contain insulin combined with substances like protamine and zinc, added to slow absorption from the injection site. These components create tiny, suspended particles that give the insulin its characteristic cloudy or milky appearance. For these types, cloudiness is an expected and functional attribute, indicating the formulation is correct and ready for use.
Identifying Cloudy Insulin Types
Specific types of insulin are formulated to be cloudy to achieve prolonged action. The primary intermediate-acting insulin that is uniformly cloudy is NPH (Neutral Protamine Hagedorn) insulin, also known as isophane insulin. NPH insulin provides a sustained release, typically working for up to 18-24 hours, with a peak effect several hours after injection.
Many premixed insulins also appear cloudy. These combine intermediate-acting NPH insulin with a rapid- or short-acting insulin in fixed ratios, such as 70/30 or 50/50. The cloudy appearance of these premixed insulins is due to the NPH component, which provides a longer-lasting effect to cover insulin needs between meals and overnight.
Proper Handling and Storage
Proper handling and storage are important for maintaining the effectiveness of cloudy insulin. Before each use, gently mix cloudy insulin to ensure the suspended particles are evenly distributed. This can be done by gently rolling the vial or pen between the palms or inverting it several times until the liquid appears uniformly milky. Avoid vigorous shaking, as this can create air bubbles that may affect accurate dosing and potentially damage the insulin protein.
Before injection, visually inspect the insulin. It should have a consistent, uniformly cloudy, or milky appearance without any clumps, “frosting” on the glass, or solid particles that do not mix. If the insulin appears clear, has lumps, flakes, or sticks to the glass, or if there is any discoloration, it should not be used and must be discarded.
Unopened vials or pens of insulin should be stored in the refrigerator until their expiration date. Once opened, insulin can generally be stored at room temperature for a specified period, often up to 28 days, but always check the manufacturer’s instructions for exact guidelines. Insulin should not be frozen or exposed to extreme heat or direct sunlight, as these conditions can damage the insulin and reduce its effectiveness.