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Insulin Glargine

Insulin glargine

Lantus Basaglar Toujeo

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Updated: December 06, 2025

Overview

Insulin glargine is a long-acting recombinant human insulin analog used to improve glycemic control in adults and children with diabetes mellitus. It provides a basal level of insulin over 24 hours with minimal peak activity, mimicking physiologic insulin secretion. This insulin analog is modified at position A21 (asparagine replaced by glycine) and has two arginines added to the B-chain C-terminus, resulting in a shift of the isoelectric point towards neutral pH. These structural changes cause the insulin to precipitate in subcutaneous tissue, creating a depot that slowly releases insulin into circulation.

Drug Class

Long-acting insulin analog Therapeutic category: Antidiabetic agent Pharmacologic class: Hormone

Mechanism of Action

Binds to insulin receptors on target cells (primarily liver, muscle, and adipose tissue) to: • Promote cellular glucose uptake • Inhibit hepatic glucose production • Promote lipogenesis and protein synthesis • Inhibit lipolysis and proteolysis The structural modifications create slow, prolonged absorption from subcutaneous tissue, providing a relatively constant concentration/time profile.

Pharmacokinetics

Absorption: Slow and prolonged due to precipitation at neutral pH in subcutaneous tissue Distribution: Similar to endogenous insulin (volume of distribution ~0.26 L/kg) Metabolism: Primarily in liver and kidneys via insulin-degrading enzyme Excretion: Minimal renal excretion (<1% unchanged) Half-life: Terminal half-life ~12 hours (duration of action up to 24 hours)

Pharmacodynamics

Produces a smooth, peakless glucose-lowering effect: • Onset: 1-1.5 hours • Maximum effect: No pronounced peak • Duration: Up to 24 hours Improves fasting plasma glucose and reduces HbA1c by 1.5-2% when used appropriately

Indications

• Treatment of type 1 diabetes mellitus (in combination with short-acting insulin) • Treatment of type 2 diabetes mellitus (as monotherapy or in combination with oral antidiabetic agents) • Long-term management of diabetes mellitus requiring basal insulin

Contraindications

Absolute: • Hypersensitivity to insulin glargine or any component • During episodes of hypoglycemia Relative: • Hypokalemia • Concurrent use with pioglitazone or other TZDs (increased risk of fluid retention and heart failure)

Dosage & Administration

Type 1 diabetes: Initial dose typically 1/3 of total daily insulin requirement as basal insulin Type 2 diabetes: Initial dose 0.2 units/kg or 10 units once daily All indications: • Administer subcutaneously once daily at the same time each day • Rotate injection sites (abdomen, thigh, or upper arm) • Dose adjustments should be made based on blood glucose monitoring

Special Populations

Pediatric: Safety and efficacy established for children ≥6 years with type 1 diabetes Geriatric: May require more conservative dosing due to increased hypoglycemia risk Renal impairment: Requires careful glucose monitoring and possible dose reduction Hepatic impairment: May require dose reduction due to reduced insulin clearance

Adverse Effects

Common (>10%): • Hypoglycemia (most frequent adverse effect) • Injection site reactions (pain, erythema) • Lipodystrophy with repeated injections Serious (<1%): • Severe hypoglycemia • Hypokalemia • Anaphylaxis • Fluid retention with heart failure (when used with TZDs)

Drug Interactions

• Beta-blockers: May mask hypoglycemia symptoms • Corticosteroids: May increase insulin requirements • Thiazides: May decrease insulin sensitivity • Alcohol: May increase hypoglycemia risk • MAO inhibitors: May increase hypoglycemia risk

Warnings & Precautions

• Risk of severe hypoglycemia (especially with renal/hepatic impairment) • Never administer intravenously or via insulin pump • May cause hypokalemia • Risk of lipodystrophy with repeated injections • Potential for medication errors (confusion with other insulins)

Pregnancy & Lactation

Pregnancy: Category C - Insulin requirements may decrease in first trimester and increase in second/third trimesters Lactation: Compatible - Insulin does not pass into breast milk in significant amounts

Monitoring Parameters

• Daily fasting blood glucose levels • Periodic HbA1c (every 3-6 months) • Serum potassium (especially in at-risk patients) • Signs/symptoms of hypoglycemia • Injection site reactions • Weight gain patterns

Patient Counseling

• Proper injection technique and site rotation • Recognition/treatment of hypoglycemia • Importance of consistent meal patterns • Never share insulin pens • Storage requirements • Importance of regular glucose monitoring • What to do if a dose is missed • Signs of allergic reactions

Storage & Stability

Unopened vials/pens: Refrigerate at 2-8°C (36-46°F) Opened vials/pens: Can be stored at room temperature (<30°C) for 28 days Do not freeze or expose to excessive heat/light

Clinical Pearls

• Do not mix with other insulins • More consistent absorption when injected in abdominal area • Patients may require dose increases during illness/stress • Consider concurrent short-acting insulin for prandial coverage • Titrate dose based on morning fasting glucose levels • Toujeo contains 300 units/mL (other formulations are 100 units/mL)

References

• American Diabetes Association. Standards of Medical Care in Diabetes - 2023 • Lantus® (insulin glargine) Prescribing Information • Nathan DM, et al. Diabetes Care. 2009;32(1):193-203 • Riddle MC, et al. Diabetes Care. 2003;26(11):3080-6