Metformin Cannot Be Directly Converted to Insulin Units
There is no direct equivalent dose conversion between metformin 2000 mg and insulin glargine (Lantus), as they are completely different medications with different mechanisms of action. 1
Understanding the Fundamental Differences
- Metformin is an oral antihyperglycemic agent that works by decreasing hepatic glucose production, decreasing intestinal glucose absorption, and improving insulin sensitivity 1
- Insulin glargine (Lantus) is a long-acting insulin analog that directly lowers blood glucose by promoting glucose uptake into cells 1
- These medications are often used at different stages of diabetes treatment or in combination, not as direct substitutes for each other 1
Transitioning from Metformin to Insulin
If a patient needs to transition from metformin to insulin glargine, the approach should be:
- Start with a low dose of insulin glargine (typically 10 IU per day) and titrate based on fasting glucose readings 1, 2
- Titration should aim for fasting plasma glucose of 4.0-5.5 mmol/L (72-99 mg/dL) 2
- In clinical trials, patients transitioning from oral agents to insulin glargine required approximately 68-70 IU/day (or 0.66-0.69 IU/kg/day) after 36 weeks of treatment 2
Combination Therapy Approach
Most commonly, metformin and insulin are used together rather than substituting one for the other:
- When adding insulin glargine to metformin 2000 mg, start with 10 IU daily at bedtime and titrate weekly 1, 3
- Self-titration can be done by increasing dose by 1 unit/day if fasting plasma glucose is >5.5 mmol/L 3
- Combination therapy with metformin and insulin has been shown to improve glycemic control and reduce insulin requirements by approximately 17% compared to insulin alone 4
Special Considerations
- For patients with chronic kidney disease (eGFR <45 mL/min/1.73 m²), metformin dose should be reduced; if eGFR <30 mL/min/1.73 m², metformin is contraindicated and insulin would be used alone 1
- In older adults, simplification of insulin regimens may be needed - if transitioning from complex insulin regimens to basal insulin only, use 70% of the total daily insulin dose as the starting basal insulin dose 1
- For patients with type 2 diabetes who need greater glucose lowering than can be obtained with oral agents, GLP-1 receptor agonists are preferred to insulin when possible 1
Common Pitfalls to Avoid
- Never abruptly discontinue metformin when starting insulin, as this can lead to worsening hyperglycemia 1, 4
- Avoid delaying intensification of treatment when glycemic targets are not met 1
- Be aware that adding insulin to metformin will likely cause some weight gain (approximately 1-2 kg more than with oral agents alone) 3
- Monitor for hypoglycemia when initiating insulin, especially in older adults 1