Insulin Glargine

Insulin glargine is a long-acting basal insulin analog, a genetically engineered version of human insulin designed to be absorbed slowly and provide steady background insulin coverage ^[2]. It differs from natural insulin by the replacement of asparagine with glycine at position A21 of the A chain and the addition of two arginine amino acids to the end of the B chain ^[2]. These modifications shift the point at which the protein is least soluble toward neutral pH, which is the basis of its prolonged action ^[2].

Developed by the company Sanofi, insulin glargine was approved in the United States in 2000 and marketed as Lantus ^[1]. It became one of the most widely used insulins worldwide, and after its patents expired a range of follow-on products and biosimilars appeared, including Basaglar and Semglee among others, along with a more concentrated formulation sold as Toujeo ^[4]. Studies of these biosimilar glargine products found them comparable in efficacy and safety to the original ^[4]. Insulin glargine is included on the World Health Organization list of essential medicines ^[2].

As a basal insulin, glargine is used in both type 1 and type 2 diabetes, usually injected once daily to control blood glucose between meals and overnight, often alongside a separate rapid-acting insulin for meals ^[2]. Its clinical value was established in the influential Treat-to-Target Trial, in which adding once-daily glargine to oral diabetes drugs allowed most people with type 2 diabetes to reach their blood-sugar goal, with significantly less nocturnal hypoglycemia than the older NPH insulin ^[1]. Later analyses of the same treat-to-target approach confirmed these findings and helped define who is most at risk of low blood sugar when starting basal insulin ^[2][3].

Insulin glargine is a clear solution supplied in vials, prefilled disposable pens, and cartridges, and it is not mixed in the same syringe with other insulins because of its acidic formulation ^[2]. Like all insulins, its main risk is hypoglycemia, and it can also cause injection-site reactions, itching, weight gain, and, occasionally, low blood potassium ^[1]. Rotating injection sites helps prevent lumps or pitting of the fat under the skin ^[1].

Insulin glargine is prescription only. The main risk is hypoglycemia, which can be severe if a dose is too high, a meal is skipped, or exercise is heavy. Other effects include weight gain, injection site reactions, lipohypertrophy at overused sites, mild fluid retention, and low potassium at high doses. Beta blockers can blunt the warning signs of low blood sugar, and combining it with other glucose-lowering drugs raises hypoglycemia risk. Do not mix insulin glargine in the same syringe with other insulins because that disrupts its slow-release behavior. Dose needs change with illness, kidney or liver problems, and steroid use.

Insulin glargine shares the interaction profile of insulin generally, and the risk runs in both directions. Sulfonylureas, GLP-1 receptor agonists, salicylates, fibrates, MAO inhibitors, ACE inhibitors and alcohol add to its glucose-lowering effect and deepen hypoglycemia; corticosteroids, thiazides, sympathomimetics, danazol, thyroid hormone and atypical antipsychotics such as olanzapine push glucose the other way and erode basal control. Beta-blockers, clonidine, guanethidine and reserpine are the dangerous middle case, because they mask the adrenergic warning signs of a falling glucose without preventing the fall.

One interaction is specific to this molecule and is physical rather than pharmacological. Glargine is formulated as a clear solution at pH 4 and works by precipitating into microcrystals once it meets neutral subcutaneous tissue. Mixing or diluting it with another insulin in the same syringe changes that pH, produces an immediate visible precipitate, and makes the onset and duration of both insulins unpredictable.

Adding insulin to a thiazolidinedione also raises the risk of fluid retention and heart failure.

Checking a whole stack? Run it through interactions + stacks.

Insulin glargine was developed by the pharmaceutical company Hoechst, later part of Aventis and then Sanofi, as the first true long-acting or basal insulin analog. Its designers made two changes to human insulin: replacing asparagine at position A21 with glycine and adding two arginine residues to the end of the B chain, raising the molecule's isoelectric point so that it stays dissolved in an acidic vial but precipitates into a slow-releasing depot at the neutral pH of subcutaneous tissue.

The analog was approved by the United States Food and Drug Administration in 2000 and launched as Lantus, which went on to become one of the best-selling medicines in the world. As patents expired, biosimilar and follow-on versions such as Basaglar, Semglee, and Abasaglar entered the market, and a concentrated formulation, Toujeo, was introduced to provide an even flatter profile. Insulin glargine is now a cornerstone of basal insulin therapy and is listed by the World Health Organization as an essential medicine.

Insulin glargine is widely regarded as the drug that made basal insulin therapy simpler and safer, offering a nearly peakless action across roughly a day so that a single daily injection can cover background insulin needs. Its landmark contribution was reducing the burden of nocturnal hypoglycemia compared with older NPH insulin while achieving similar overall glucose control, a benefit that reshaped how type 1 and type 2 diabetes are managed.

Clinicians and patients value its predictability and once-daily convenience, and its enormous real-world use has generated a deep body of safety data. The arrival of biosimilars has also made effective basal insulin considerably more affordable in many markets. In fairness, no basal insulin is entirely peakless in every individual, and hypoglycemia risk remains higher in leaner, younger patients or those on certain oral agents, so dosing still calls for individual titration.