What is the proper procedure for administering insulin to a patient with type 1 or type 2 diabetes mellitus (DM), considering their current blood glucose level, medical history, and potential allergies or sensitivities to insulin?

How to Administer Insulin

Insulin should be injected subcutaneously into the abdomen (fastest absorption), upper arms, anterior/lateral thighs, or buttocks, using 4-mm pen needles at a 90-degree angle, with systematic rotation within one anatomical area rather than switching between different body regions. 1, 2

Injection Site Selection and Technique

Choose the abdomen for most injections as it provides the fastest and most consistent absorption, followed by arms, thighs, and buttocks in descending order of absorption speed. 1 Avoid a 2-inch radius around the navel. 1, 2

Proper Needle Selection and Insertion

• Use 4-mm pen needles as first-line choice for all patient categories, including those with obesity, as they are effective, safe, less painful, and minimize risk of intramuscular injection. 1, 3
• Insert at a 90-degree angle directly into subcutaneous tissue. 1, 4
• Avoid intramuscular injection, which causes unpredictable absorption and frequent unexplained hypoglycemia, particularly dangerous with long-acting insulins. 1, 3

Site Rotation Protocol

Rotate injections systematically within one anatomical area (e.g., different spots within the abdomen) rather than switching between different body regions with each injection. 1, 2 This practice decreases day-to-day variability in absorption. 1

Examine injection sites regularly for lipohypertrophy (soft, smooth raised areas several centimeters wide) and never inject into these areas, as they cause erratic insulin absorption, increased glycemic variability, and unexplained hypoglycemia. 1

Timing of Administration

Rapid-Acting Insulin (Lispro, Aspart, Glulisine)

• Administer 0-15 minutes before meals for patients eating normally. 1, 2, 3
• If oral intake is poor or uncertain, give immediately after the patient eats or count carbohydrates and cover the amount actually ingested. 1

Basal Insulin (Glargine, Detemir, Degludec, NPH)

• Give once daily at the same time each day, typically at bedtime. 2
• When transitioning from IV to subcutaneous insulin, administer basal insulin 2-4 hours before discontinuing the IV infusion at 60-80% of the 24-hour IV insulin dose. 1

Dosing Regimens by Patient Type

Type 1 Diabetes

Start with 0.5 units/kg/day total daily dose, split as 50% basal insulin and 50% prandial insulin divided among three meals. 1, 2 This requires multiple daily injections combining premeal rapid-acting insulin with once-daily long-acting basal insulin. 1, 3

Type 2 Diabetes (Insulin-Naive)

Begin with 10 units of basal insulin once daily or use weight-based dosing of 0.1-0.2 units/kg/day. 2 For severe hyperglycemia (glucose >400 mg/dL), start with 0.3-0.5 units/kg/day split between basal and prandial components. 2, 4

Hospitalized Patients (Non-Critical)

Use scheduled basal-bolus regimen (basal + nutritional + correction insulin) for patients with good oral intake. 1 For patients with poor intake or NPO status, use basal plus correction insulin only. 1 Never use sliding scale insulin alone as it is strongly discouraged and associated with worse outcomes. 1

Critical Care Patients

Administer continuous IV insulin infusion targeting glucose 140-180 mg/dL, using protocols with demonstrated safety and low hypoglycemia rates. 1

Dose Titration Protocol

Adjust basal insulin based on fasting glucose:

• If fasting glucose 140-179 mg/dL: increase by 2 units every 3 days 2, 4
• If fasting glucose ≥180 mg/dL: increase by 4 units every 3 days 2, 4
• Target fasting glucose: 80-130 mg/dL 2, 4

Adjust prandial insulin based on pre-meal and 2-hour postprandial glucose, increasing by 1-2 units or 10-15% every 3 days to achieve postprandial glucose <180 mg/dL. 4

If hypoglycemia occurs (glucose <70 mg/dL), immediately reduce insulin dose by 10-20% unless clearly explained by missed meal or other reversible factor. 1, 2, 4

Critical Safety Measures

Hypoglycemia Prevention

Instruct all insulin-using patients to carry at least 15 grams of fast-acting carbohydrate at all times for treating hypoglycemic reactions. 1, 4 Train family members, roommates, and coworkers in glucagon administration for type 1 diabetes patients who cannot take oral carbohydrates. 1

Reassess the insulin regimen when glucose falls below 100 mg/dL to prevent hypoglycemia. 1 Modification is required when glucose <70 mg/dL. 1

Monitoring Requirements

Check fasting blood glucose daily during titration and pre-meal glucose before each meal for patients on prandial insulin. 2, 4 Self-monitoring of blood glucose is essential for all insulin users due to day-to-day variability influenced by insulin absorption, exercise, stress, food absorption, and hormonal changes. 1

Special Circumstances

Continue insulin during illness even if unable to eat or vomiting, as illness increases insulin requirements. 1 More frequent monitoring is required during illness, travel, or any change in routine. 1

Exercise increases absorption rate from injection sites, so consider timing and site selection accordingly. 1 Increased skin temperature from sunbathing or hot water also accelerates absorption. 1

Common Pitfalls to Avoid

Never inject into areas of lipohypertrophy, as this causes unpredictable absorption and glycemic variability. 1

Do not use needles longer than 4-6 mm in children due to high risk of intramuscular injection. 3

Avoid rotating between different anatomical areas with each injection, as this increases absorption variability. 1, 2

Do not rely on sliding scale insulin alone in any setting, as scheduled basal-bolus regimens provide superior glycemic control. 1, 4

Ensure medical identification (bracelet or wallet card) is worn by all insulin users. 1