Basal Bolus Insulin Prescribing

Basal bolus insulin gives a long-acting insulin to cover fasting needs and rapid-acting insulin before meals to cover carbohydrate and correct high readings. It is the regimen for type 1 diabetes and the intensive regimen in type 2 diabetes when basal insulin is not enough.

Physiology. About 40 to 50% of the total daily dose is basal and 50 to 60% is mealtime insulin.

Flexibility. Mealtime doses can be fixed, or adjusted by carbohydrate counting and correction.

Basal insulin. Glargine U100, detemir, degludec or isophane at bedtime.

Mealtime insulin. Rapid-acting analogues (aspart, lispro, glulisine) given 0 to 15 minutes before eating give better post-meal control than human soluble insulin, which is injected 30 minutes before eating.

Type 2 diabetes. Add mealtime insulin to the largest meal first, then to others as needed, while continuing metformin and organ-protective drugs.

Total daily dose. 0.4 to 0.6 units/kg in adults with type 1 diabetes (about 0.5 units/kg). Use 0.3 to 0.4 units/kg in the first year of type 1 diabetes, in older adults, and in kidney impairment. Children need higher weight-based doses, set by paediatric specialists.

Split. Basal 40 to 50%; the remainder divided among 3 meals in proportion to meal size.

Type 2 diabetes. Add 4 units, or 10% of the basal dose, before the largest meal, and increase by 1 to 2 units (10 to 15%) every 3 days, set by the next pre-meal or 2 hour post-meal glucose. Reduce the basal dose if it exceeds 0.5 units/kg.

Carbohydrate ratio. Estimate grams of carbohydrate covered by 1 unit using 500 divided by the total daily dose, then adjust by experience.

Correction factor. Estimate the fall in glucose for each unit using 100 divided by the total daily dose (in mmol/L). Add correction when glucose is over target before meals, and not within 3 to 4 hours of the last dose.

Missed or skipped meals. Skip the mealtime dose if the meal is skipped. Never omit basal insulin in type 1 diabetes.

Hypoglycaemia treatment. Give 15 to 20 g fast-acting carbohydrate; recheck at 15 minutes. Glucagon 1 mg intramuscularly or subcutaneously for severe hypoglycaemia.

Special groups. - Kidney impairment: reduce total dose by 25% at eGFR 10 to 50. - Liver disease: lower doses with careful titration. - Pregnancy: insulin requirements rise through pregnancy and fall after delivery; specialist-led. - Breastfeeding: reduce insulin by about 10 to 20% in the first weeks. - Older adults: simplify the regimen. - Exercise: reduce mealtime insulin before planned activity.

Monitoring. Capillary glucose before meals and at bedtime, with occasional post-meal and 03:00 checks; continuous glucose monitoring where available. HbA1c every 3 months. Ketone testing during illness in type 1 diabetes.

Sick-day rules. Never stop basal insulin. Check glucose and ketones every 3 to 4 hours. Seek urgent care for vomiting, ketones of 1.5 mmol/L or more, or glucose persistently over 15 mmol/L.

Stopping or stepping down. Simplify to basal only when type 2 diabetes control allows and mealtime doses are small.

Referral and escalation. Refer to a diabetes team for recurrent hypoglycaemia, ketoacidosis, pregnancy, or unstable control.