Insulin glargine (Lantus, Abasaglar, Toujeo, Semglee): long-acting insulin explained

Insulin is a medicine that helps the body use glucose for energy. The NHS explains that in type 1 diabetes the body cannot produce insulin, so insulin must be prescribed to stop blood glucose rising too high, and that in type 2 diabetes it is needed when other medicines no longer keep glucose in a healthy range. Insulin glargine is a long-acting analogue designed to lower glucose slowly and steadily across the day.

The NHS lists the long-acting insulin brands as Abasaglar, Lantus, Levemir, Semglee, Toujeo and Tresiba, covering insulin detemir, glargine and degludec. Insulin glargine includes Lantus, Abasaglar, Semglee and Toujeo. The manufacturer leaflet for Abasaglar says the medicine is used to treat diabetes mellitus in adults, adolescents and children aged 2 years and above.

The NHS adds that Levemir, a different long-acting insulin, is being discontinued, with supplies expected to last until late 2026, and that people taking it should talk to their diabetes team about changing. The NHS names insulin glargine brands among the long-acting options, and your diabetes team will advise which is right for you.

For type 1 diabetes, the NHS says most people take both a long-acting insulin once or twice a day (the background or basal insulin) and a rapid-acting insulin before meals, a regimen sometimes called basal bolus. Insulin glargine may be recommended if you cannot take insulin detemir or prefer fewer injections, and it is usually taken once a day. If you use an insulin pump you only need rapid-acting insulin, because the pump gives small doses throughout the day and night.

For type 2 diabetes, the NHS says people who need insulin usually take either a long-acting or intermediate-acting insulin once or twice a day, with or without separate rapid-acting insulin before meals, or a mixed insulin. Intermediate-acting insulin such as Humulin I or Insulatard is usually recommended first, and a long-acting insulin such as Lantus, Toujeo, Semglee or Abasaglar may be suggested if you often get low blood sugar or need help from a carer to take injections. Sometimes insulin is only needed for a short time, for example when ill, pregnant or newly diagnosed.

The leaflet says your doctor may tell you to use it in combination with a short-acting insulin or with tablets for high blood sugar. The NHS stresses that the type of insulin and dose may change over time and that your diabetes care team recommends the treatment they think is best for you.

The leaflet says you need one injection of Abasaglar each day at the same time of day, under the skin, using the area your doctor shows you and changing the puncture site within the area with each injection. Do not inject it into a vein. The NHS says insulin is injected with an insulin pen, which helps you inject safely and take the right dose, and that your diabetes nurse will show you where to inject and how to use the pen.

The dose is set by your doctor from your lifestyle, glucose results and previous insulin use. The leaflet says your doctor will tell you how much you need per day, when to check blood sugar, and when to inject more or less. Many factors influence blood sugar, so learn the leaflet’s guidance for high and low levels.

Always attach a new needle before each pen use, perform the safety test, check the insulin is clear, colourless and water-like, and never share a pen, as the leaflet instructs. Check the pack and label before each injection to avoid mix-ups with other insulins.

The Abasaglar leaflet says that if you miss a dose or are unsure how much you have injected, your blood sugar may become too high, so check it frequently and do not take a double dose. Do not stop the insulin without speaking to a doctor, because stopping can lead to severe high blood sugar and ketoacidosis.

The leaflet says hypoglycaemia (low blood sugar) can be very serious and is very common with insulin treatment, affecting more than 1 in 10 people. If your blood sugar falls too low you may pass out, and serious hypoglycaemia may cause brain damage and may be life-threatening. It tells you to act immediately to raise blood sugar, and it describes a box at the end of the leaflet with treatment guidance. Know your own warning signs, and make sure family or colleagues know what to do.

Beta-blockers and some other medicines may weaken or suppress the first warning symptoms of low blood sugar, so tell your team about your medicines. Your ability to concentrate or react may be reduced during low or high blood sugar; the leaflet advises contacting your doctor about driving if you have frequent hypos or reduced warning symptoms.

Skin changes can occur if you inject too often at the same place: fatty tissue may shrink (lipoatrophy) or thicken (lipohypertrophy), and lumps can occur. The insulin may not work well if you inject into a lumpy area, so rotate sites and tell your doctor if you are injecting into a lump. Common side effects include redness, pain, itching, hives or swelling at the injection site, most disappearing in days to weeks.

Rare effects include severe allergic reactions (skin reactions all over the body, swelling of skin or mucous membranes, shortness of breath, fall in blood pressure), temporary vision changes when blood sugar control changes markedly, and swelling of the calves and ankles. Tell a doctor straight away for signs of severe allergic reaction. Some people with type 2 diabetes and heart disease taking pioglitazone with insulin developed heart failure, so report unusual breathlessness, rapid weight gain or swelling.

If you are ill or have a major injury your blood sugar may rise, and if you are not eating enough it may fall. The leaflet says to contact a doctor early and, if you have type 1 diabetes, not to stop your insulin and to continue to get enough carbohydrates. Always tell people treating you that you need insulin.

Medicines that can lower blood sugar include other diabetes medicines, ACE inhibitors, fluoxetine, MAO inhibitors, aspirin and sulphonamide antibiotics. Those that can raise it include corticosteroids, diuretics, oestrogens and progestogens, thyroid hormones, salbutamol and some antipsychotics and HIV medicines; others, such as beta-blockers, clonidine and lithium, can make it rise or fall. Alcohol may make blood sugar either rise or fall.

Before travelling, talk to your doctor about insulin supplies, storage, timing across time zones and what to do in an emergency. If you are planning pregnancy or are pregnant, tell your doctor, since insulin doses may need to change during pregnancy and after birth, and careful control and prevention of hypoglycaemia is important for your baby.

If you take insulin glargine and a new medicine is added, ask whether it affects your blood sugar and what to do, and check your levels more closely when you start or stop it.

Insulin is prescribed on the NHS through GPs and diabetes teams, and private diabetes specialists use the same products. Whoever prescribes, the plan should cover your target glucose, who you call if levels are persistently high or low, and what to do when unwell. Ask for a named contact in your diabetes team and a written sick-day plan.