Insulin types and why peak time is the whole question
Insulin questions are timing questions in disguise. If a stem tells you which insulin was given and at what time, it is almost always asking when the client is at greatest risk for hypoglycaemia, or when a meal or snack must be available. Rapid-acting insulins such as lispro and aspart begin working in about 15 minutes and peak in roughly one hour, so food must be on the tray before or immediately after administration. Regular insulin begins in about 30 minutes and peaks between two and four hours.
Intermediate-acting NPH insulin begins in one to two hours and peaks between four and twelve hours, which makes late afternoon or overnight hypoglycaemia the classic scenario after a morning dose. Long-acting insulins such as glargine and detemir have no pronounced peak and provide roughly 24 hours of basal coverage. Because glargine is peakless, it is never mixed with another insulin in the same syringe.
Two mechanical rules recur. When mixing, draw air into the NPH vial, then air into the regular vial, then withdraw regular first and NPH second — clear before cloudy — so that the longer-acting suspension never contaminates the clear vial. And only regular insulin is administered intravenously, which matters for diabetic ketoacidosis management.
Storage and technique teaching includes refrigerating unopened vials, keeping the in-use vial at room temperature for up to about 28 days, rotating injection sites within one anatomical region to prevent lipohypertrophy, not massaging the site, and never shaking a vial vigorously. Insulin pens are not shared between clients under any circumstances.
| Type | Example | Onset | Peak | Nursing implication |
|---|---|---|---|---|
| Rapid | Lispro, aspart | 10–20 min | 30–90 min | Food must be present at the bedside |
| Short | Regular | 30 min | 2–4 h | Only insulin given intravenously |
| Intermediate | NPH | 1–2 h | 4–12 h | Cloudy; afternoon hypoglycaemia risk |
| Long | Glargine, detemir | 1–2 h | No true peak | Never mix in a syringe; once daily |
Oral and injectable non-insulin agents
Metformin is first-line for type 2 diabetes. It reduces hepatic glucose production and does not cause hypoglycaemia when used alone. Two facts dominate exam items: it must be withheld before and for 48 hours after iodinated contrast studies because of the risk of contrast-induced kidney injury leading to lactic acidosis, and lactic acidosis itself presents with muscle pain, weakness, unusual somnolence, hyperventilation and abdominal discomfort. Gastrointestinal upset early in therapy is common and usually settles.
Sulfonylureas such as glipizide and glyburide stimulate insulin release from the pancreas and therefore do cause hypoglycaemia, particularly in older adults and when meals are skipped. They also interact with alcohol to produce a disulfiram-like reaction. Meglitinides work similarly but briefly and are taken with meals, with the instruction to skip the dose if the meal is skipped.
Newer agents each carry a signature teaching point. GLP-1 agonists such as semaglutide and liraglutide slow gastric emptying, promote weight loss and carry warnings for pancreatitis and thyroid C-cell tumours. SGLT2 inhibitors ending in -flozin cause glucose excretion in urine and predispose to genital mycotic infections, dehydration and euglycaemic ketoacidosis. DPP-4 inhibitors ending in -gliptin are weight neutral with a pancreatitis caution.
Whenever a stem combines an antidiabetic drug with a beta blocker, expect a hypoglycaemia-masking question. Beta blockers blunt tachycardia, tremor and palpitations, so diaphoresis may be the only warning sign the client experiences.
- •Metformin: no hypoglycaemia alone; hold around contrast dye
- •Sulfonylureas: real hypoglycaemia risk, especially in older adults
- •Meglitinides: with meals; skip the dose if the meal is skipped
- •GLP-1 agonists: nausea, weight loss, pancreatitis warning
- •SGLT2 inhibitors: genital infections, dehydration, euglycaemic DKA
Hypoglycaemia, sick days and client teaching
Hypoglycaemia is a blood glucose below 70 mg/dL and presents with shakiness, diaphoresis, tachycardia, hunger, irritability, confusion and, if untreated, seizures and loss of consciousness. In a conscious client with a patent swallow, use the rule of 15: give 15 grams of fast-acting carbohydrate such as four ounces of juice, three or four glucose tablets or a tablespoon of honey, wait 15 minutes and recheck. Repeat once if still low, then follow with a protein and carbohydrate snack if the next meal is more than an hour away.
In an unconscious client or one who cannot swallow safely, nothing goes in the mouth. Give intramuscular or subcutaneous glucagon, or 50 percent dextrose intravenously if access exists, then reassess and provide oral carbohydrate once alert. Nausea and vomiting after glucagon are expected, so position the client to protect the airway.
Sick-day rules are a reliable exam topic. Clients continue taking insulin even when not eating normally, because illness raises glucose through stress hormones. They should monitor glucose every three to four hours, check urine or blood ketones, maintain fluid intake, substitute easily tolerated carbohydrates, and contact the provider for persistent vomiting, ketones, or glucose consistently above 240 mg/dL.
Foot care and long-term monitoring round out the teaching: inspect feet daily including between the toes, wash with warm not hot water and dry thoroughly, never go barefoot, do not cut corns or calluses, wear well-fitting shoes, and have an HbA1c checked roughly every three months with a general target under 7 percent. Practise with the insulin and diabetes guide and our pharmacology question bank.
- •Below 70 mg/dL: rule of 15, recheck in 15 minutes
- •Unconscious: glucagon or IV dextrose, nothing by mouth
- •Never omit insulin during illness
- •Check ketones when glucose exceeds 240 mg/dL
- •Daily foot inspection; HbA1c target generally under 7 percent