Short answer: Insulin labels say extra insulin can cause low blood sugar and low potassium. Mild lows can usually be treated with sugar by mouth; severe lows with coma, seizure or confusion may need glucagon or glucose through a vein. The labels add that a low can come back after it seems over, so more carbohydrate and watching may be needed. How long the risk lasts depends on how long the insulin acts.
The overdosage section (10) of the Lantus and Humalog labels reads almost the same. Excess insulin "may cause hypoglycemia and hypokalemia" (low blood sugar and low potassium). Mild lows can usually be treated with sugar by mouth, and the dose, meals or exercise may need adjusting. More severe lows with coma, seizure or neurologic problems may be treated with glucagon or concentrated glucose through a vein.
Then a warning that matters for the hours after: "hypoglycemia may recur after apparent clinical recovery," so ongoing carbohydrate and observation may be needed. The Afrezza label gives the Poison Help line (1-800-222-1222) for an overdose.
The Lantus label (section 5.6) explains that all insulins move potassium from the blood into cells, which can lower blood potassium. It says untreated low potassium "may cause respiratory paralysis, ventricular arrhythmia, and death." This is one reason a large overdose is handled by a medical team rather than at home.
The Humalog label (section 5.3) says the risk of a low after an injection is tied to how long the insulin acts and is usually highest when its effect peaks. A rapid-acting mealtime insulin and a long-acting basal insulin therefore behave differently after an extra dose.
For a sense of scale, the Lantus label reports a clamp study in type 1 diabetes where the effect of Lantus lasted a median of 24 hours, which was the end of the observation window, compared with 14.5 hours for NPH insulin.
The NIDDK steps for a low below target or under 70 mg/dL: take 15 to 20 grams of glucose or carbohydrate, such as four glucose tablets, half a cup of juice or a tablespoon of sugar; wait 15 minutes and check again; repeat until back in range; and have a snack if the next meal is more than an hour away. For a severe low the person cannot treat alone, it names glucagon and calling 911. See when glucagon is used.
Both labels (section 5.4) say accidental mix-ups between insulin products have been reported and ask that the label be checked before every injection, which matters most for people who use a mealtime and a basal insulin. The Humalog label adds that drawing U-200 insulin out of its pen into a syringe can cause an overdose.
A dose log answers the question of whether a dose was already taken. Dose Track logs each dose with the time, so the answer is one tap away, and a missed or extra dose can be raised with the prescriber or pharmacist with the facts in hand.
Read more on Dose Track: Hypoglycemia (low blood sugar) · Basal insulin · Missed a Lantus dose · Log a dose in Dose Track