Actrapid FlexPen: Uses, Dosage & Side Effects
A rapid-acting human insulin in a convenient pre-filled disposable pen, used to control blood sugar in people with diabetes mellitus
Actrapid FlexPen is a rapid-acting human insulin supplied in a convenient pre-filled, disposable injection pen. It is used to lower high blood sugar in people with diabetes mellitus (type 1 and type 2). The FlexPen contains soluble human insulin produced by recombinant DNA technology and begins working approximately 30 minutes after subcutaneous injection, with a blood sugar-lowering effect lasting about 8 hours. Actrapid FlexPen comes ready to use and is discarded when empty, making it a practical choice for people who prefer not to load cartridges into reusable pens. Human insulin is classified as an essential medicine by the World Health Organization and is one of the most widely prescribed diabetes treatments worldwide.
Quick Facts: Actrapid FlexPen
Key Takeaways
- Actrapid FlexPen is a rapid-acting soluble human insulin in a disposable pre-filled pen that starts working within 30 minutes and lasts approximately 8 hours, ideal for mealtime blood sugar control.
- You must eat a meal or snack containing carbohydrates within 30 minutes of injecting to prevent dangerously low blood sugar (hypoglycemia).
- The FlexPen is a single-use device — it cannot be refilled. Discard the entire pen when empty or after 6 weeks of use, whichever comes first.
- Always rotate injection sites to prevent skin changes (lipodystrophy), and never share pens or needles with another person, even if the needle is changed.
- Store unopened FlexPens in the refrigerator (2–8°C); once in use, keep at room temperature (up to 30°C) for a maximum of 6 weeks.
What Is Actrapid FlexPen and What Is It Used For?
Actrapid FlexPen is a rapid-acting (soluble) human insulin manufactured by Novo Nordisk using recombinant DNA technology. The term “FlexPen” refers to the delivery device — a pre-filled, disposable injection pen that comes ready to use straight from the packaging. Unlike the Actrapid Penfill cartridge (which requires a separate reusable pen), the FlexPen is an all-in-one device that is simply discarded when empty. Both products contain the same active ingredient — unmodified human insulin at 100 IU/ml — and work identically once injected.
The FlexPen design offers several practical advantages. It eliminates the need to insert cartridges into a reusable pen device, reducing the risk of handling errors. The pen features a clear dose window and a simple dial mechanism that makes it straightforward to select the correct dose. It delivers doses from 1 to 60 units in increments of 1 unit. These features make the FlexPen particularly suitable for people who are new to insulin therapy, those with dexterity difficulties, or patients who travel frequently and prefer a device that requires minimal preparation.
Diabetes mellitus is a chronic metabolic condition characterised by the body's inability to produce sufficient insulin or to use insulin effectively. In type 1 diabetes, the immune system destroys the insulin-producing beta cells of the pancreas, leading to absolute insulin deficiency. These patients require lifelong insulin replacement from the time of diagnosis. In type 2 diabetes, the body becomes resistant to insulin's effects and may eventually lose the ability to produce adequate amounts. Many people with advanced type 2 diabetes require insulin therapy when oral medications alone no longer provide sufficient blood sugar control.
Actrapid FlexPen is designed for mealtime (prandial) use. When you eat food containing carbohydrates, your blood sugar rises. The soluble insulin in Actrapid provides a burst of insulin activity that helps your cells absorb this glucose, preventing dangerous post-meal blood sugar spikes. It begins to lower blood sugar approximately 30 minutes after subcutaneous injection, reaches its peak effect between 1.5 and 3.5 hours, and has a total duration of action of approximately 7 to 8 hours. Because of this 30-minute onset, patients should inject Actrapid approximately half an hour before eating.
Actrapid FlexPen is most commonly prescribed as part of a basal-bolus insulin regimen. In this approach, a longer-acting insulin (such as insulin glargine, insulin detemir, or isophane insulin) provides a steady background level of insulin throughout the day and night, while Actrapid is injected before each main meal to manage the post-meal blood sugar rise. This combination closely mimics the natural pattern of insulin secretion in people without diabetes. According to the International Diabetes Federation, approximately 537 million adults worldwide live with diabetes. Human insulin is included on the WHO Model List of Essential Medicines, reflecting its critical importance in global healthcare. Actrapid FlexPen is approved for use in adults, adolescents, and children requiring insulin treatment.
What Should You Know Before Taking Actrapid FlexPen?
Contraindications
You should not use Actrapid FlexPen in the following circumstances:
- Allergy: If you are allergic (hypersensitive) to human insulin or any of the other ingredients in Actrapid (zinc chloride, glycerol, metacresol, sodium hydroxide, hydrochloric acid, or water for injections).
- Hypoglycemia: If you feel the onset of hypoglycemia (low blood sugar symptoms such as sweating, trembling, rapid heartbeat, confusion, or dizziness), do not inject additional insulin.
- Damaged product: If the FlexPen has been dropped, damaged, or crushed, do not use it as the dosing mechanism may be compromised.
- Improper storage: If the insulin has not been stored correctly or has been frozen, it must be discarded.
- Appearance: If the solution is not clear and colorless, or if visible particles or cloudiness are present, do not use it.
- Expiry date: Never use the FlexPen after the expiry date printed on the label and outer carton.
Warnings and Precautions
Before and during treatment with Actrapid FlexPen, discuss the following important considerations with your healthcare provider:
- Kidney, liver, or endocrine problems: If you have impaired kidney or liver function, or conditions affecting the adrenal glands, pituitary gland, or thyroid, your insulin requirements may change significantly. Your doctor may need to adjust your dose and increase the frequency of blood sugar monitoring.
- Physical activity changes: If you exercise more than usual or wish to change your diet significantly, your blood sugar levels can be affected and your insulin dose may need adjustment. Increased physical activity generally lowers blood sugar, potentially requiring a reduction in insulin dose or additional carbohydrate intake.
- Illness: If you become unwell with an infection, fever, or other illness, your insulin requirements may increase even if you are eating less. Continue taking your insulin and contact your healthcare provider for guidance on dose adjustments. Never stop insulin therapy without medical supervision.
- Travel: Travelling across time zones can affect your insulin schedule and requirements. Discuss adjustments with your doctor before travelling internationally. When flying, always carry your insulin in hand luggage — the cargo hold can reach freezing temperatures that permanently destroy insulin.
- Switching insulins: If you are changed from another type of insulin (e.g., animal insulin, a different brand, or an insulin analogue) to Actrapid, your dose may need to be adjusted. Only switch insulin types under medical supervision.
Repeatedly injecting in the same area can cause the fat tissue under the skin to thicken (lipohypertrophy), shrink (lipoatrophy), or develop lumps caused by amyloid protein deposits (cutaneous amyloidosis). Insulin may not work as effectively if injected into an area with these changes. Always rotate your injection site within the same body region to help prevent these skin changes. If you notice any changes at injection sites, inform your doctor before switching to a different area, as your blood sugar monitoring and insulin dose may need adjustment.
Pregnancy and Breastfeeding
If you are pregnant, believe you may be pregnant, or are planning to become pregnant, consult your doctor before using Actrapid. Insulin is the preferred treatment for diabetes during pregnancy because it does not cross the placenta in significant amounts and is considered safe for the developing baby. Maintaining careful blood sugar control during pregnancy is critically important to prevent complications for both mother and child, including pre-eclampsia, macrosomia (large baby), birth defects, and neonatal hypoglycemia.
Insulin requirements typically change throughout pregnancy. They may decrease during the first trimester and then increase significantly during the second and third trimesters as insulin resistance increases. After delivery, insulin needs usually drop rapidly and may require prompt adjustment. Careful monitoring by your healthcare team is essential throughout pregnancy and the postpartum period.
There are no restrictions on using Actrapid during breastfeeding. Insulin does not pass into breast milk in a way that could affect the nursing infant. However, your insulin dose and dietary plan may need to be adjusted during breastfeeding, as lactation can lower blood sugar levels.
Use in Children and Adolescents
Actrapid FlexPen can be used in children and adolescents of all ages who require insulin therapy for diabetes. The FlexPen’s dose dial allows precise adjustments in 1-unit increments, which is particularly useful for children who often require smaller doses. Dosing must be individually determined by a paediatric endocrinologist based on the child's age, weight, blood sugar levels, physical activity, and growth stage. Parents and caregivers must be thoroughly trained in injection technique, blood sugar monitoring, and recognising and treating hypoglycemia. Insulin requirements may change during puberty and periods of rapid growth.
Driving and Operating Machinery
Your ability to concentrate and react may be impaired if you experience hypoglycemia (low blood sugar) or hyperglycemia (high blood sugar). This could put you and others at risk when driving or operating machinery. Ask your doctor whether it is safe for you to drive if you frequently experience low blood sugar episodes or if your warning symptoms of hypoglycemia are weakened or absent (hypoglycemia unawareness). Carry a source of fast-acting sugar in your vehicle at all times.
Sodium Content
Actrapid FlexPen contains less than 1 mmol sodium (23 mg) per dose, meaning it is essentially sodium-free. This is relevant for patients on a controlled sodium diet.
How Does Actrapid FlexPen Interact with Other Drugs?
Drug interactions with insulin are clinically significant because they can either increase or decrease blood sugar levels, sometimes unpredictably. Understanding these interactions is essential for safe diabetes management. Your doctor may need to adjust your Actrapid dose when you start, stop, or change the dose of another medication. Always inform your healthcare team about every medication you are taking.
Drugs That May Lower Blood Sugar (Increase Hypoglycemia Risk)
The following medications can enhance the blood sugar-lowering effect of Actrapid. When these drugs are used in combination with insulin, your risk of hypoglycemia increases and closer blood sugar monitoring is recommended:
| Drug/Class | Primary Indication | Interaction Mechanism |
|---|---|---|
| Other antidiabetic drugs (metformin, sulfonylureas, GLP-1 agonists) | Diabetes | Additive blood sugar-lowering effect |
| MAO inhibitors (e.g. moclobemide, phenelzine) | Depression | May potentiate insulin effect and reduce counter-regulatory response |
| Beta-blockers (e.g. atenolol, metoprolol, propranolol) | High blood pressure, heart conditions | May enhance insulin action; also mask hypoglycemia warning signs |
| ACE inhibitors (e.g. enalapril, ramipril, lisinopril) | High blood pressure, heart failure | May increase insulin sensitivity |
| Salicylates (e.g. aspirin, high doses) | Pain, inflammation, fever | Reduces hepatic glucose production |
| Anabolic steroids (e.g. testosterone) | Hormone replacement, muscle wasting | Increases insulin sensitivity and glucose uptake |
| Sulfonamide antibiotics | Bacterial infections | May enhance insulin secretion and effect |
Drugs That May Raise Blood Sugar (Decrease Insulin Effectiveness)
The following medications can counteract the effects of insulin and raise blood sugar levels. An increase in Actrapid dose may be required when starting these medications:
| Drug/Class | Primary Indication | Interaction Mechanism |
|---|---|---|
| Oral contraceptives (oestrogen/progestogen) | Contraception | Increases insulin resistance |
| Thiazide diuretics (e.g. hydrochlorothiazide) | High blood pressure, fluid retention | Impairs insulin secretion, potassium depletion |
| Glucocorticoids (e.g. prednisolone, dexamethasone) | Inflammation, autoimmune conditions | Increases insulin resistance and hepatic glucose output |
| Thyroid hormones (e.g. levothyroxine) | Hypothyroidism | Increases glucose absorption and production |
| Sympathomimetics (e.g. adrenaline, salbutamol, terbutaline) | Asthma, allergic reactions | Stimulates glycogenolysis and gluconeogenesis |
| Growth hormone (somatropin) | Growth hormone deficiency | Counter-regulatory to insulin; increases blood glucose |
| Danazol | Endometriosis, fibrocystic breast disease | Interferes with glucose metabolism |
Drugs with Variable Effects on Blood Sugar
Octreotide and lanreotide, used for acromegaly (a rare hormonal disorder involving excess growth hormone production), may either raise or lower blood sugar levels depending on the individual circumstances. These medications require particularly careful blood sugar monitoring when used alongside insulin therapy.
Beta-blockers deserve special attention because, in addition to potentially lowering blood sugar, they can mask the typical warning signs of hypoglycemia — particularly the rapid heartbeat and trembling that normally alert patients to falling blood sugar levels. If you take a beta-blocker, you may need to rely on other symptoms (such as sweating or hunger) and more frequent blood glucose testing to detect low blood sugar.
Pioglitazone (an oral diabetes medication) used in combination with insulin has been associated with heart failure in some patients with long-standing type 2 diabetes and pre-existing heart disease or previous stroke. If you take pioglitazone with insulin, inform your doctor immediately if you experience signs of heart failure such as unusual shortness of breath, rapid weight gain, or localised swelling (oedema).
Alcohol
Alcohol can affect your insulin requirements unpredictably. It may initially raise blood sugar (particularly sweet or mixed drinks) but can cause a delayed and prolonged drop in blood sugar levels, especially when consumed without food. The liver prioritises metabolising alcohol over releasing glucose, impairing the body's ability to correct low blood sugar. If you choose to drink alcohol, do so in moderation, always eat food alongside it, monitor your blood sugar more frequently, and be aware that symptoms of hypoglycemia can be mistaken for intoxication by others.
Always tell your doctor or pharmacist about all medications you are taking, including prescription drugs, over-the-counter medicines, herbal supplements, and vitamins. Never start or stop a medication without discussing the potential impact on your blood sugar control with your healthcare provider.
What Is the Correct Dosage of Actrapid FlexPen?
The dosage of Actrapid FlexPen is highly individualised and there is no single dose that works for everyone. Your doctor will determine your starting dose and make adjustments over time based on regular blood sugar monitoring, HbA1c levels, your diet, physical activity, body weight, other medications, and any concurrent illnesses. The overall aim of insulin therapy is to maintain blood sugar levels as close to normal as possible while minimising the risk of hypoglycemia.
Adults
Standard Mealtime Dosing
Actrapid FlexPen is injected subcutaneously 30 minutes before a meal containing carbohydrates. The FlexPen can deliver doses from 1 to 60 units in increments of 1 unit. In a typical basal-bolus regimen, mealtime insulin (such as Actrapid) accounts for approximately 50–60% of the total daily insulin dose, divided across main meals, while the remaining 40–50% is provided by a longer-acting basal insulin given once or twice daily.
Combination with Basal Insulin
Actrapid FlexPen is most often used together with an intermediate-acting insulin such as Insulatard (isophane/NPH insulin) or a long-acting insulin analogue such as insulin glargine (Lantus) or insulin detemir (Levemir). If your doctor changes you from one type of insulin to another, your dose may need to be adjusted. Only switch insulin types under medical supervision.
Children and Adolescents
Paediatric Dosing
Actrapid FlexPen can be used in children and adolescents of all ages. The 1-unit increment dial makes it well suited for the precise dosing that children often require. The dose is individually determined by the child's paediatric endocrinologist based on age, weight, blood sugar levels, physical activity, and growth stage. Insulin requirements may change significantly during puberty and periods of rapid growth. Parents and caregivers must be trained in injection technique, blood sugar monitoring, and hypoglycemia management.
Elderly Patients
Older Adults (65+ years)
In elderly patients, progressive deterioration of kidney function may lead to a gradual decrease in insulin requirements. If you are over 65, you should monitor your blood sugar more regularly and discuss any changes in your insulin dose with your doctor. Blood sugar targets may be less strict in older adults to reduce the risk of hypoglycemia, which can be particularly dangerous in this population due to increased fall risk and cardiovascular vulnerability. The FlexPen’s clear dose window and simple dial mechanism can be helpful for elderly patients.
Kidney or Liver Impairment
If you have impaired kidney or liver function, your insulin requirements may be reduced because insulin is metabolised and cleared more slowly. More frequent blood sugar monitoring is essential, and your doctor may need to adjust your dose accordingly.
How and Where to Inject
Actrapid FlexPen is injected subcutaneously (under the skin) only. It must never be injected into a vein (intravenously) or a muscle (intramuscularly), as this would dramatically alter its absorption and could cause severe and unpredictable blood sugar changes. The FlexPen is compatible with NovoFine and NovoTwist injection needles.
The recommended injection sites include:
- Abdomen (front of the waist): Provides the fastest and most consistent absorption. This is the preferred site when rapid onset is desired.
- Buttocks: Good alternative injection site with reliable absorption.
- Front of thighs: Slightly slower absorption compared to the abdomen.
- Upper arms: Suitable but may be difficult to self-inject.
Rotate injection sites within the same body region at each injection to reduce the risk of lipodystrophy (skin thickening, shrinking, or lumps at injection sites). Always use a new needle for every injection. After inserting the needle, hold it under the skin for at least 6 seconds with the injection button fully pressed to ensure the complete dose is delivered. Remove and safely discard the needle after each injection — never store the FlexPen with a needle attached, as this can cause leakage, air bubbles, and inaccurate dosing.
The Actrapid FlexPen is a disposable, pre-filled pen designed for single use only. It must not be refilled. When the pen is empty, discard it properly and start using a new one. If you use both Actrapid FlexPen and another insulin pen, keep them clearly separated to prevent mix-ups — always check the label and insulin colour before every injection. Always carry a spare FlexPen in case the one in use is lost or damaged.
Missed Dose
If you forget to take your Actrapid before a meal, your blood sugar may rise too high (hyperglycemia). Do not take a double dose to make up for a forgotten injection. Check your blood sugar more frequently and contact your doctor or diabetes nurse for guidance if your blood sugar remains elevated. For information on managing hyperglycemia, see the side effects section below.
Overdose
If you inject too much Actrapid, your blood sugar may drop to dangerously low levels (hypoglycemia). For mild symptoms (sweating, trembling, hunger), immediately consume 15–20 grams of fast-acting carbohydrates such as glucose tablets, fruit juice, or sugar-sweetened drinks. Recheck your blood sugar after 15 minutes and repeat if necessary. Severe hypoglycemia — where you are unable to treat yourself or become unconscious — is a medical emergency. Someone nearby should administer a glucagon injection and call emergency services immediately. Do not give food or drink to an unconscious person.
Stopping insulin therapy abruptly, especially in type 1 diabetes, can lead to diabetic ketoacidosis (DKA) — a life-threatening condition where the body breaks down fat instead of sugar for energy, causing a dangerous build-up of acids (ketones) in the blood. Symptoms include excessive thirst, frequent urination, nausea, vomiting, abdominal pain, rapid deep breathing, facial flushing, and drowsiness. DKA requires immediate hospital treatment. Very high blood sugar and ketoacidosis can lead to diabetic coma and, if untreated, death. Never stop or reduce your insulin without your doctor's guidance.
What Are the Side Effects of Actrapid FlexPen?
Like all medicines, Actrapid FlexPen can cause side effects, although not everyone experiences them. Understanding the potential side effects and their frequency helps you recognise them early and take appropriate action. The side effects listed below are classified by how commonly they occur according to international pharmacovigilance standards:
Very Common
May affect more than 1 in 10 people
- Hypoglycemia (low blood sugar) — The most frequent and potentially most serious side effect. Can occur if you inject too much insulin, eat too little, skip a meal, exercise more than usual, or drink alcohol. Symptoms include cold sweating, cool pale skin, headache, rapid heartbeat, nausea, intense hunger, temporary visual disturbances, drowsiness, unusual tiredness and weakness, anxiety, trembling, nervousness, confusion, and difficulty concentrating. Severe hypoglycemia can lead to loss of consciousness, seizures, brain damage, and — if prolonged and untreated — death.
Uncommon
May affect up to 1 in 100 people
- Local allergic reactions — Pain, redness, hives (urticaria), inflammation, bruising, swelling, and itching at the injection site. These reactions usually resolve within a few weeks of continued treatment. If they persist or spread beyond the injection site, contact your doctor immediately.
- Visual disturbances — At the start of insulin treatment or when blood sugar control changes rapidly, temporary changes in vision may occur. These are usually transient and resolve as blood sugar levels stabilise.
- Swollen joints — When starting insulin therapy, the body may temporarily retain fluid, causing swelling around the ankles and other joints. This usually resolves on its own; if it persists, consult your doctor.
- Painful neuropathy — If blood sugar levels improve very rapidly, nerve-related pain (acute painful neuropathy) may occur. This is typically temporary and self-limiting.
- Lipodystrophy — Changes in fat tissue at injection sites, including thickening (lipohypertrophy) or shrinking (lipoatrophy). These can affect insulin absorption and are prevented by rotating injection sites consistently.
Very Rare
May affect up to 1 in 10,000 people
- Severe allergic reactions (systemic anaphylaxis) — Life-threatening allergic reactions that can include widespread skin reactions, swelling of the face or throat, difficulty breathing, rapid heartbeat, sweating, nausea, vomiting, and a drop in blood pressure. This is a medical emergency — seek immediate medical help and call emergency services.
- Diabetic retinopathy worsening — In patients with pre-existing diabetic retinopathy (diabetic eye disease), very rapid improvement in blood sugar control can paradoxically cause a temporary worsening of retinopathy. Discuss this risk with your eye doctor if you have diabetic eye disease.
Not Known (Frequency Cannot Be Estimated)
Reported from post-marketing experience
- Cutaneous amyloidosis — Lumps under the skin caused by accumulation of amyloid protein. If you inject into an area with lumps, insulin may not be absorbed effectively. Change injection sites regularly to help prevent this condition.
Recognising and Managing Hypoglycemia
Because hypoglycemia is the most important side effect of Actrapid, understanding how to recognise and manage it is crucial for every person using insulin:
Step 1: Do not inject more insulin. Immediately consume 15–20 grams of fast-acting sugar: glucose tablets, sugar cubes, fruit juice, or a sugar-sweetened drink. Artificial sweeteners do NOT help.
Step 2: Follow up with a slower-acting carbohydrate (bread, crackers, or a meal) to prevent blood sugar from dropping again.
Step 3: Check your blood sugar after 15 minutes. If it is still low, repeat step 1.
Step 4: When symptoms have resolved and blood sugar has stabilised, resume your normal insulin treatment.
If unconscious: Someone nearby must administer a glucagon injection and call emergency services immediately. Do NOT attempt to give food or drink to an unconscious person. Once consciousness is regained, give glucose or a sugary snack. If there is no response to glucagon, hospital treatment is required.
Inform people around you — family, friends, colleagues — that you have diabetes and what the consequences of hypoglycemia can be. Tell them that if you become unconscious, they should place you on your side (recovery position) and call emergency services immediately. They must not give you food or drink, as there is a risk of choking.
Recognising and Managing Hyperglycemia
Hyperglycemia (high blood sugar) can occur if you have not injected enough insulin, if you forget a dose, if you eat more than usual, or if you exercise less than planned. Warning symptoms develop gradually and include: increased urination, thirst, loss of appetite, nausea or vomiting, drowsiness or fatigue, facial flushing, dry skin, dry mouth, and a fruity-smelling breath (acetone). These symptoms may indicate diabetic ketoacidosis — a serious, life-threatening condition that occurs when the body breaks down fat instead of sugar because of insufficient insulin. If you experience these symptoms, test your blood sugar and urine for ketones immediately and contact your doctor or seek emergency medical care urgently.
How Should You Store Actrapid FlexPen?
Proper storage of insulin is critical for maintaining its effectiveness. Insulin that has been stored incorrectly may lose its potency without any visible changes, leading to unexpectedly poor blood sugar control. Follow these guidelines to ensure your Actrapid FlexPen remains safe and effective:
Unopened (Not Yet in Use)
- Store in a refrigerator at 2–8°C
- Do not place near the freezer compartment — freezing permanently damages insulin
- Do not freeze — frozen insulin must be discarded and never used
- Keep in the outer carton to protect from light
- Check the expiry date (EXP) before use — the expiry date refers to the last day of the stated month
In Use or Carried as a Spare
- Store at room temperature up to 30°C
- Do not refrigerate or freeze once in use
- Can be kept at room temperature for up to 6 weeks
- Always keep the pen cap on when not in use to protect from light
- Discard after 6 weeks of first use, even if insulin remains in the pen
- Do not leave the FlexPen in direct sunlight, in a car on a warm day, or near a heat source
Inspect the insulin before use. Actrapid should be a clear, colorless, water-like solution with no visible particles or cloudiness. Do not use if the solution appears cloudy, discoloured, or contains any solid particles. If you notice unexpectedly poor blood sugar control, your insulin may have lost effectiveness due to improper storage — replace it with a fresh FlexPen.
Remove and safely discard the injection needle after every use. Keep insulin and all medicines out of the sight and reach of children. Do not dispose of FlexPens or needles via household waste or sewage. Use a sharps disposal container for needles and return unused or expired FlexPens to your pharmacy for safe, environmentally responsible disposal.
What Does Actrapid FlexPen Contain?
Active Ingredient
The active substance is human insulin (insulinum humanum). Each millilitre of solution contains 100 IU (international units) of human insulin. Each FlexPen contains 3 ml, providing a total of 300 IU per pen. The human insulin in Actrapid is produced by recombinant DNA technology in Saccharomyces cerevisiae (baker's yeast) and is structurally identical to the insulin produced naturally by the human pancreas. This ensures high purity and consistent quality with minimal risk of immunological reactions compared to older animal-derived insulin preparations.
As a soluble (neutral) insulin, the insulin molecules in Actrapid are fully dissolved in the solution, which is why the preparation appears clear and colorless. This soluble form enables rapid absorption after subcutaneous injection, providing the quick onset of action that characterises mealtime insulin coverage.
Inactive Ingredients (Excipients)
| Ingredient | Purpose |
|---|---|
| Zinc chloride | Stabilises insulin hexamers and assists in prolonging action |
| Glycerol | Tonicity agent (makes the solution isotonic with body fluids) |
| Metacresol | Preservative (antimicrobial agent to prevent bacterial growth) |
| Sodium hydroxide | pH adjustment |
| Hydrochloric acid | pH adjustment |
| Water for injections | Solvent (vehicle for the active ingredient) |
Actrapid FlexPen contains less than 1 mmol sodium (23 mg) per dose, meaning it is essentially sodium-free. This is relevant for patients on controlled sodium diets.
Available Forms and Pack Sizes
Actrapid FlexPen is available as a clear, colorless solution for injection in a 3 ml pre-filled, disposable pen (FlexPen). Each pen contains 300 IU of human insulin and can deliver doses from 1 to 60 units in 1-unit increments. The pens are packaged in cartons containing 1, 5, or 10 pens. Not all pack sizes may be available in all countries. The FlexPen is compatible with NovoFine and NovoTwist injection needles, which are sold separately.
Manufacturer
Actrapid FlexPen is manufactured by Novo Nordisk A/S, Novo Allé, DK-2880 Bagsværd, Denmark. Novo Nordisk is one of the world's leading producers of insulin and diabetes care products, with over 100 years of experience in insulin development and manufacturing. They also operate manufacturing facilities in Chartres, France, and other locations worldwide to ensure reliable global supply.
Frequently Asked Questions About Actrapid FlexPen
Both contain the same active ingredient — soluble human insulin at 100 IU/ml — and work identically once injected. The difference is in the delivery device. The FlexPen is a pre-filled, disposable pen that comes ready to use and is discarded when empty. The Penfill is a cartridge that must be loaded into a separate Novo Nordisk reusable injection pen. The FlexPen is often preferred for its convenience, especially for people who travel frequently, are new to insulin injections, or prefer a simpler device with fewer assembly steps.
Actrapid begins lowering blood sugar approximately 30 minutes after injection. If you do not eat a meal or snack containing carbohydrates within this timeframe, the insulin will continue to lower your blood sugar without the incoming glucose from food to balance it, leading to hypoglycemia (low blood sugar). The timing of the injection relative to your meal is important for safe and effective blood sugar control. If circumstances prevent you from eating within 30 minutes, contact your healthcare provider for guidance.
The Actrapid FlexPen can deliver from 1 to 60 units per injection in increments of 1 unit. If your prescribed dose exceeds 60 units, you will need to give yourself two or more injections. The dose selector on the FlexPen will click back to 0 if you try to dial more units than remain in the pen, which serves as a helpful safeguard. Always check the dose window before injecting to confirm you have selected the correct number of units.
No, you must never share your FlexPen with another person, even if you change the needle. Sharing pens carries a serious risk of cross-contamination and transmission of blood-borne infections, including hepatitis and HIV. Each person using insulin must have their own individual pen device. Your FlexPen is prescribed specifically for your dose and treatment plan.
If your Actrapid FlexPen has been frozen, you must discard it immediately and use a fresh pen. Freezing permanently damages the insulin protein, rendering it ineffective even though the solution may still appear clear after thawing. Using frozen-and-thawed insulin can lead to unpredictable blood sugar control and potentially dangerous hyperglycemia. To prevent accidental freezing, do not store FlexPens directly against the back wall of the refrigerator (which is often the coldest area) or in contact with the freezer compartment. When travelling in cold weather, keep insulin close to your body for warmth rather than in outer bags or luggage compartments.
Actrapid contains unmodified human insulin, which is structurally identical to the insulin your body naturally produces. Rapid-acting insulin analogues (such as insulin lispro, insulin aspart, and insulin glulisine) have been chemically modified to be absorbed more quickly. Analogues typically start working in 10–15 minutes (versus 30 minutes for Actrapid) and can be injected immediately before or even during a meal. However, Actrapid has a slightly longer duration of action. Your doctor will choose the most appropriate insulin type for your individual circumstances, considering factors such as lifestyle, meal patterns, and blood sugar control targets.
References
- World Health Organization. WHO Model List of Essential Medicines – 23rd List. Geneva: WHO; 2023. Human insulin is classified as an essential medicine for diabetes management worldwide.
- European Medicines Agency. Actrapid (Soluble Human Insulin) – Summary of Product Characteristics. EMA; 2024. Official European prescribing information for soluble human insulin.
- American Diabetes Association. Standards of Care in Diabetes – 2025. Diabetes Care. 2025;48(Suppl 1). Comprehensive evidence-based clinical practice recommendations for diabetes management.
- Davies MJ, Aroda VR, Collins BS, et al. Management of Hyperglycemia in Type 2 Diabetes, 2022. A Consensus Report by the ADA and EASD. Diabetes Care. 2022;45(11):2753-2786. doi:10.2337/dci22-0034
- International Diabetes Federation. IDF Diabetes Atlas, 10th edition. Brussels: IDF; 2021. Global epidemiological data on diabetes prevalence and projections.
- Novo Nordisk A/S. Actrapid FlexPen – Patient Information Leaflet. Bagsværd, Denmark: Novo Nordisk; 2020. Official patient information for Actrapid FlexPen pre-filled pens.
- Hirsch IB. Insulin analogues. New England Journal of Medicine. 2005;352(2):174-183. doi:10.1056/NEJMra040832. Comprehensive review of insulin pharmacology and clinical applications.
- DeWitt DE, Hirsch IB. Outpatient insulin therapy in type 1 and type 2 diabetes mellitus: scientific review. JAMA. 2003;289(17):2254-2264. doi:10.1001/jama.289.17.2254
- Holman RR, Thorne KI, Farmer AJ, et al. Addition of biphasic, prandial, or basal insulin to oral therapy in type 2 diabetes. New England Journal of Medicine. 2007;357(17):1716-1730. doi:10.1056/NEJMoa075392
- U.S. Food and Drug Administration. Insulin Human Injection – Prescribing Information. FDA; 2024. Official U.S. prescribing information for soluble human insulin products.
Editorial Team
This article has been written and reviewed by the iMedic medical editorial team according to our strict editorial standards. Our team consists of licensed physicians, pharmacists, and medical researchers with expertise in endocrinology, diabetology, and clinical pharmacology.
Content developed by iMedic's medical writing team based on current international guidelines (WHO, EMA, FDA, ADA, EASD) and peer-reviewed endocrinological research.
Independently reviewed and fact-checked by the iMedic Medical Review Board, comprising board-certified specialists in endocrinology, diabetology, and clinical pharmacology.
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