What subcutaneous (Sc) insulin should I use?

Subcutaneous Insulin Selection

For subcutaneous insulin therapy, use rapid-acting insulin analogs (such as insulin lispro, aspart, or glulisine) as your first-line choice for prandial coverage, combined with basal insulin (NPH or long-acting analogs) for comprehensive glycemic control. 1

Recommended Insulin Regimen Structure

For Patients with Good Oral Intake

A basal-bolus regimen is the preferred approach, consisting of:

• Basal insulin: Provides background insulin coverage throughout the day 1
• Prandial (bolus) insulin: Rapid-acting analog administered immediately before each meal 1
• Correction insulin: Additional rapid-acting insulin to correct hyperglycemia 1

This regimen significantly improves glycemic control and reduces hospital complications compared to sliding scale insulin alone. 1

For Patients with Poor or No Oral Intake

Use basal insulin alone or basal plus correction insulin rather than prandial doses, as nutritional intake is unpredictable. 1

Specific Insulin Types and Their Uses

Rapid-Acting Insulin Analogs (Preferred for Prandial Coverage)

Insulin lispro (Humalog), aspart, or glulisine are the recommended rapid-acting options:

• Onset: Within 15 minutes of administration 2, 3
• Peak: 30-90 minutes after injection 3
• Duration: Less than 5 hours 3
• Timing: Administer immediately before meals (0-5 minutes) 4
• Advantage: Better postprandial glucose control compared to regular human insulin 1, 5, 4

These analogs provide superior postprandial glycemic control without increasing hypoglycemia risk compared to regular human insulin. 6, 5

Regular Human Insulin (Alternative)

If rapid-acting analogs are unavailable:

• Timing: Must be given 20-30 minutes before meals 4
• Disadvantage: Delayed onset leads to higher postprandial glucose and increased risk of late hypoglycemia 7

Basal Insulin Options

NPH insulin or long-acting analogs (glargine, detemir, degludec):

• NPH: Administered 2-3 times daily 8
• Long-acting analogs: Once or twice daily dosing
• Both provide similar glycemic control in hospital settings 1

Special Clinical Scenarios

Continuous Tube Feeding

Use NPH insulin administered every 8-12 hours to match continuous carbohydrate delivery:

• Divide total daily dose into 2-3 equal portions 8
• Example: 68 units morning, 34 units evening for twice-daily dosing 8
• Add correctional rapid-acting insulin every 4-6 hours as needed 8

Critical safety point: If tube feeding is interrupted, immediately start 10% dextrose infusion at 50 mL/hr to prevent hypoglycemia. 8

Insulin Pump Therapy (CSII)

Rapid-acting insulin analogs (such as lispro) are the appropriate choice for continuous subcutaneous insulin infusion:

• Confirmed stability in pump reservoirs 1
• Superior postprandial control compared to regular insulin 1
• Never mix different insulin types in pumps 1, 2
• Change reservoir every 7 days, infusion sets every 3 days 2

Important caveat: Rapid-acting analogs are not FDA-approved for use in pregnancy when delivered via pump. 1

Premixed Insulin Formulations

Premixed insulins (such as 70/30 formulations) are NOT recommended for routine hospital use due to significantly increased hypoglycemia risk compared to basal-bolus regimens, despite comparable glycemic control. 1

If used in outpatient settings:

• Administer twice daily, 30 minutes before breakfast and dinner 9
• Start with 10 units or 0.1-0.2 units/kg/day divided into two doses 9

Transitioning from IV to Subcutaneous Insulin

Administer subcutaneous basal insulin 2-4 hours before discontinuing IV insulin:

• Convert at 60-80% of total daily IV insulin dose 1
• This prevents rebound hyperglycemia and reduces morbidity 1

Critical Pitfalls to Avoid

Never Use Sliding Scale Insulin as Sole Therapy

Sliding scale insulin alone is strongly discouraged in hospitalized patients, as it is reactive rather than preventive and leads to poor glycemic control. 1

Timing Errors with Regular Insulin

Regular human insulin requires 20-30 minute pre-meal administration. 4 Patients often inject too close to meals, causing postprandial hyperglycemia and delayed hypoglycemia. 5

Mixing Insulin Inappropriately

• Only mix rapid-acting analogs with NPH insulin for subcutaneous injection 2
• Draw rapid-acting insulin first, then NPH 2
• Inject immediately after mixing 2
• Never mix insulins in pump reservoirs 2

Inadequate Monitoring After Dose Changes

Monitor blood glucose every 4-6 hours after any insulin adjustment to promptly identify hypo- or hyperglycemia. 8

Practical Administration Guidelines

For Eating Patients

• Perform point-of-care glucose testing immediately before meals 1
• Administer rapid-acting insulin right before eating 1, 4
• If intake is poor, give insulin immediately after the meal with dose adjusted for actual carbohydrate consumed 1

Hypoglycemia Prevention

• Implement a standardized protocol for blood glucose <70 mg/dL 1
• Review and adjust insulin regimen whenever glucose drops below 70 mg/dL 1
• Patients at high risk (renal/hepatic impairment, erratic food intake) require more frequent monitoring and dose reductions 2