Insulin Glargine

Insulin Glargine is prescribed to treat:

• Diabetes mellitus (type 1 and type 2) • Various related conditions in the diabetes category • Associated symptoms and complications

It is an important medication that helps manage these conditions effectively.

Insulin glargine (Lantus, Basaglar, Toujeo) is a long-acting basal insulin analogue used in type 1 and type 2 diabetes. It provides the background insulin the body needs continuously, independent of meals, and it was the first analogue to deliver that reliably enough to displace older intermediate-acting preparations.

Mechanism of Action

Insulin glargine is human insulin modified so that it is soluble at the acidic pH of the injection solution but precipitates into microcrystals in subcutaneous tissue at physiologic pH. Those microcrystals dissolve slowly, releasing insulin gradually over roughly 24 hours.

The result is a relatively flat, peakless profile — which is the entire point. Physiologic basal insulin secretion is continuous and low-level, suppressing hepatic glucose production between meals and overnight. Older intermediate-acting insulins such as NPH have a pronounced peak several hours after injection, which frequently landed overnight and caused nocturnal hypoglycemia. Glargine's flatter profile substantially reduces that risk, particularly at night, and is why it became standard.

Basal insulin does not cover meals. In type 1 diabetes it must be paired with rapid-acting insulin at meals such as insulin lispro. In type 2 diabetes, basal insulin alone is often sufficient initially, because residual endogenous insulin secretion still handles some of the post-meal load.

Toujeo is a more concentrated formulation with an even flatter, longer profile. Concentrated insulins are not interchangeable unit-for-unit with standard preparations by volume, and mixing them up is a recognised source of serious dosing error.

Clinical Use

In type 2 diabetes, basal insulin is typically added when oral agents and non-insulin injectables no longer achieve glycemic targets. It is titrated against fasting glucose, since that is what basal insulin controls — a simple and often patient-led adjustment: increase the dose every few days until fasting glucose reaches target, then stop.

The most common error is over-basalisation: pushing the basal dose ever higher to control glucose readings that are actually post-meal elevations. Basal insulin cannot fix post-meal excursions, and continuing to raise it produces overnight and between-meal hypoglycemia while daytime readings stay high. A rising basal dose that is not improving fasting glucose signals that the problem is elsewhere — mealtime coverage, or a need for a GLP-1 agonist such as semaglutide rather than more insulin.

Insulin is also the point at which weight gain and hypoglycemia enter a regimen that may have been free of both, which is why current guidance places GLP-1 receptor agonists ahead of insulin for most patients with type 2 diabetes who need injectable therapy. Where insulin is genuinely needed, combining it with a GLP-1 agonist allows lower insulin doses. The understanding your A1C article covers targets, and our endocrine team manages insulin initiation and titration.

Injection Technique and Practical Issues

Technique determines absorption more than most patients realise. Rotating injection sites prevents lipohypertrophy — thickened, rubbery subcutaneous tissue that develops where injections are repeatedly given in the same spot. Insulin absorbed from lipohypertrophic tissue is erratic and typically reduced, which produces unexplained glucose variability that looks like a dosing problem and is not.

Lipohypertrophy is common, easy to find by examining and palpating injection sites, and routinely missed because nobody looks. A patient with unexplained swings whose sites have never been examined is a patient whose sites should be examined.

Needles are single-use; reusing them blunts the tip and contributes to lipohypertrophy. Insulin in use can be kept at room temperature for a limited period, while unopened supplies are refrigerated — insulin should never be frozen, and it degrades at high temperatures, which matters in a Florida car or an unairconditioned room.

Pens and vials are not interchangeable in technique, and the different glargine products are not automatically substitutable at the pharmacy. A patient switched between them without dose review is a common source of unexpected glucose change. The MedlinePlus insulin glargine entry covers administration in detail.

Monitoring and Follow-Up

Fasting glucose guides basal titration; A1c every three months until stable and every six months thereafter tracks overall control. Continuous glucose monitoring, where available, reveals overnight patterns and hypoglycemia that fingerstick testing misses entirely, and it changes management more often than any other single addition.

Hypoglycemia should be asked about specifically at every visit, including nocturnal symptoms — night sweats, vivid dreams, waking with headache — which patients rarely connect to their insulin. Hypoglycemia unawareness, where the adrenergic warning symptoms are lost after repeated episodes, is dangerous and warrants relaxing targets to allow recovery.

Glycemic targets should be individualised. A tight A1c target in an older patient with hypoglycemia risk trades a distant microvascular benefit for immediate risk of falls and hospitalisation. The American Diabetes Association publishes patient-level guidance on how targets are set.

Special Populations

In older adults, hypoglycemia risk is higher, symptoms are more often atypical — confusion or a fall rather than sweating and tremor — and consequences are more severe. Simpler regimens and looser targets are frequently the safer choice, and deintensification is an active decision worth revisiting.

In kidney impairment, insulin requirements fall as the kidney contributes to insulin clearance, and doses often need reducing as function declines. In pregnancy, insulin is the preferred glucose-lowering therapy and requirements change substantially across trimesters. Illness raises requirements even when eating less — the sick-day rule is that basal insulin is generally continued, not stopped, in type 1 diabetes, because stopping it precipitates ketoacidosis.

When to Contact Your Doctor

Learn to recognise and treat hypoglycemia: shakiness, sweating, confusion, irritability, palpitations, or hunger. Treat immediately with fast-acting carbohydrate and recheck. Seek emergency care for severe hypoglycemia with confusion, seizure, or loss of consciousness, and ensure someone close to you knows how to use glucagon.

Report recurrent hypoglycemia, which means the regimen needs changing rather than more vigilance. Report loss of the usual warning symptoms. Report unexplained glucose variability, and ask to have your injection sites examined. Never stop basal insulin during illness if you have type 1 diabetes; contact us instead for a sick-day plan.

To review your insulin regimen, address hypoglycemia, or discuss whether a non-insulin option would suit you better, contact us or schedule a visit.