NovoRapid Flexpen100 IU/ml

NovoRapid Flexpen is a premixed (biphasic) insulin formulation combining a protamine-crystallized, intermediate-acting insulin aspart component with a rapid-acting soluble insulin aspart component. It is FDA-approved and widely used for the following indication:

• Glycemic control in diabetes mellitus: Indicated to improve glycemic control in adults with type 1 or type 2 diabetes mellitus who require insulin therapy.

Limitations of use: NovoRapid Flexpen is not recommended for treatment of diabetic ketoacidosis, and because the two components are fixed in a set ratio, the rapid-acting and intermediate-acting portions cannot be dosed independently of one another.

Each mL of Protamine Crystallised Insulin Aspart suspension (100 units/mL, U-100) typically contains 70% insulin aspart protamine crystals (intermediate-acting) and 30% soluble insulin aspart (rapid-acting), produced by recombinant DNA technology using Saccharomyces cerevisiae (baker's yeast). Inactive ingredients commonly include protamine sulfate, zinc, phenol, metacresol, glycerol, disodium hydrogen phosphate dihydrate, sodium chloride, and water for injection, with hydrochloric acid or sodium hydroxide added as needed to adjust pH.

NovoRapid Flexpen is a biphasic (premixed) human insulin analogue suspension. It combines a rapid-acting insulin aspart fraction, which begins lowering blood glucose within minutes of injection, with a protamine-crystallized insulin aspart fraction that dissolves and acts more slowly, providing intermediate-duration glucose control. This dual action allows a single injection to cover both a meal-related glucose rise and a longer background insulin requirement. It appears as a white, uniformly cloudy suspension that must be resuspended before each use.

NovoRapid Flexpen belongs to the therapeutic class of premixed (biphasic) rapid- and intermediate-acting insulin analogues, used in the pharmacologic management of diabetes mellitus.

Mechanism of Action

Protamine Crystallised Insulin Aspart works primarily through regulation of glucose metabolism. Insulin aspart binds to insulin receptors on target tissues (skeletal muscle and adipose tissue), promoting cellular uptake of glucose and inhibiting hepatic glucose output. It also inhibits lipolysis and proteolysis while enhancing protein synthesis.

Pharmacodynamics

The rapid-acting (soluble) fraction has an onset of action within 10-20 minutes, while the protamine-crystallized fraction dissolves gradually to provide an intermediate-acting effect. Following a 0.3 unit/kg subcutaneous dose, peak activity occurs at approximately 2.7 ± 0.9 hours, with a total duration of action of up to 24 hours.

Pharmacokinetics

A single amino acid substitution (proline to aspartic acid at position B28) in the rapid-acting fraction of Protamine Crystallised Insulin Aspart reduces self-association (hexamer formation), allowing faster subcutaneous absorption of that portion compared with regular human insulin. Mean peak serum concentration is reached at approximately 85 minutes, and serum insulin levels return to baseline by 16-20 hours after injection. Plasma protein binding is low (less than 10%).

NovoRapid Flexpen is for subcutaneous injection only (abdomen, thigh, buttock, or upper arm). It must never be given intravenously or through an insulin pump. Resuspend thoroughly before each dose and rotate injection sites. See Dosage and Administration for complete instructions.

Many medicines can alter the glucose-lowering effect of NovoRapid Flexpen, increasing the risk of hypoglycemia or hyperglycemia. Report all medicines, including over-the-counter drugs and herbal products, to the prescribing physician.

Drugs that may increase hypoglycemia risk

Other antidiabetic agents, ACE inhibitors, angiotensin receptor blockers, disopyramide, fibrates, fluoxetine, monoamine oxidase inhibitors (MAOIs), pentoxifylline, pramlintide, salicylates, somatostatin analogues, and sulfonamide antibiotics.

Drugs that may decrease glucose-lowering effect (risk of hyperglycemia)

Corticosteroids, thiazide diuretics, atypical antipsychotics, danazol, estrogens/progestogens (including oral contraceptives), glucagon, isoniazid, niacin, protease inhibitors, somatropin, sympathomimetics (e.g., epinephrine, albuterol), and thyroid hormones.

Drugs with variable effect

Alcohol, beta-blockers, clonidine, and lithium may either potentiate or weaken the blood-glucose-lowering effect.

Drugs that mask hypoglycemia symptoms

Beta-blockers, clonidine, guanethidine, and reserpine can blunt the warning signs of hypoglycemia (such as tremor and palpitations), delaying recognition and treatment.

The most common and most serious adverse effect of NovoRapid Flexpen is hypoglycemia, which can range from mild to severe and, if untreated, may result in seizure, unconsciousness, or death.

Other reported side effects

• Injection site reactions (redness, swelling, itching)
• Lipodystrophy (thickening or pitting of fat) at injection sites with repeated use in the same spot
• Weight gain
• Peripheral edema (fluid retention), especially when starting insulin or intensifying therapy
• Headache
• Upper respiratory tract infection, pharyngitis, rhinitis
• Diarrhea and dyspepsia
• Allergic reactions ranging from mild local rash to rare severe generalized hypersensitivity/anaphylaxis

Pregnancy

Poorly controlled diabetes during pregnancy increases the risk of complications to both mother and fetus, so good glycemic control is important. Data specific to this exact combination product in pregnancy are limited; published data on insulin aspart itself have not shown an association with major birth defects. NovoRapid Flexpen should be used in pregnancy only under close medical supervision, with the dose individualized and adjusted as insulin requirements typically change during pregnancy.

Lactation

Insulin is a normal component of human milk, and limited data suggest it does not pose a specific risk to the breastfed infant. However, insulin requirements may need adjustment during breastfeeding, and use of NovoRapid Flexpen while breastfeeding should be guided by a physician, weighing the benefits of breastfeeding against any potential effects.

Use NovoRapid Flexpen only under medical supervision, with the following precautions:

• Hypoglycemia: The principal risk of therapy; patients and caregivers must be educated to recognize and promptly treat low blood glucose. Risk increases with changes in meal timing/content, unusual physical activity, alcohol intake, renal or hepatic impairment, and certain concomitant medications (see Interactions).
• Never share insulin pens or needles between patients, even after a needle change, due to risk of transmitting blood-borne infections.
• Medication errors: Always confirm the insulin product and dose before each injection to avoid mix-ups with other insulin products.
• Do not switch to a different insulin product/brand or strength without medical supervision, as this may require dose adjustment.
• Hypersensitivity reactions: Discontinue immediately and seek medical attention if signs of a generalized allergic reaction (rash over the whole body, shortness of breath, wheezing, hypotension, rapid pulse, or sweating) occur.
• Hypokalemia: Insulin therapy can cause a shift of potassium into cells and lower serum potassium; monitor in patients at risk (e.g., those on potassium-lowering medicines or with reduced renal function).
• Fluid retention/heart failure: Using thiazolidinediones (TZDs) together with insulin, including this product, can cause fluid retention and heart failure, particularly in patients with pre-existing heart failure risk factors.
• Renal and hepatic impairment: May reduce insulin clearance and increase hypoglycemia risk; monitor glucose closely and adjust dose as needed.
• Do not use if the suspension has failed to resuspend to a uniform, cloudy white appearance, or if clumps or particles remain visible.

Overdose of NovoRapid Flexpen causes hypoglycemia, which may also be accompanied by hypokalemia. Mild hypoglycemic episodes can usually be managed with oral glucose or sugary food/drink. Severe hypoglycemia, associated with confusion, seizures, or unconsciousness, is a medical emergency and requires immediate medical attention — treatment may include glucagon injection or intravenous glucose administered by trained personnel, along with monitoring and correction of potassium levels. Anyone who has overdosed or is unable to take oral glucose should be taken to the nearest emergency department or have emergency medical services contacted immediately; do not attempt to manage severe hypoglycemia at home alone.

Unopened vials/pens of NovoRapid Flexpen should be stored in a refrigerator (2°C to 8°C), protected from light, and must not be frozen; discard if frozen. Once in use (opened), vials and pens may be kept at room temperature (below 30°C), away from direct heat and light, and should be discarded after 28 days even if insulin remains, whether refrigerated or kept at room temperature. Keep out of reach of children.

Pediatric Use

Safety and efficacy of NovoRapid Flexpen have not been established in children.

Geriatric Use

Elderly patients may have reduced ability to recognize hypoglycemia; conservative initial dosing and cautious dose titration are recommended, with close glucose monitoring.

Renal Impairment

Insulin requirements may be reduced in renal impairment due to decreased insulin clearance; monitor blood glucose closely and adjust dose to reduce hypoglycemia risk.

Hepatic Impairment

Insulin requirements may be reduced in hepatic impairment; monitor blood glucose closely and adjust dose as needed.

Diabetes mellitus is a chronic condition, and NovoRapid Flexpen is generally used long-term (often lifelong) as part of ongoing diabetes management. Duration and regimen should be reviewed regularly by the treating physician and adjusted according to glycemic control, changes in health status, and any transition to other therapies.

Premixed (biphasic) rapid-acting/intermediate-acting insulin analogue.

Protamine Crystallised Insulin Aspart lowers blood glucose by binding insulin receptors, thereby stimulating peripheral glucose uptake by muscle and fat tissue and suppressing hepatic glucose production; it also inhibits lipolysis and proteolysis and promotes protein synthesis. The soluble (rapid-acting) fraction acts quickly after injection, while the protamine-crystallized fraction dissolves more slowly to extend the duration of glucose-lowering action.

Safety and effectiveness of NovoRapid Flexpen have not been established in pediatric patients. Use in children should occur only under specialist medical supervision if considered clinically necessary, with careful individualized dosing and monitoring.