Metformin Should Be Discontinued in ICU Patients
Metformin must be discontinued in patients admitted to the ICU, regardless of oral intake status, due to the substantially elevated risk of metformin-associated lactic acidosis (MALA) in critically ill patients. 1
Rationale for Discontinuation in the ICU
The ICU setting presents multiple overlapping risk factors that dramatically increase MALA risk:
- Tissue hypoxia and hypoperfusion from sepsis, shock, or respiratory failure create conditions of anaerobic metabolism that impair lactate clearance 1, 2
- Acute kidney injury occurs in a high proportion of critically ill patients, reducing metformin clearance and causing drug accumulation 3, 4
- Hepatic dysfunction impairs lactate metabolism, as the liver is the primary site of lactate removal 2
- Hemodynamic instability and use of vasopressors indicate tissue hypoperfusion states where metformin is contraindicated 1, 2
The mortality rate associated with MALA approaches 50%, making prevention through discontinuation the most critical intervention 3, 5.
Specific ICU Contraindications
Metformin should be stopped immediately when patients have:
- Sepsis or systemic infection with hemodynamic instability 2
- Acute kidney injury or anticipated renal impairment 2
- Hypoxic states including respiratory failure or severe hypoxemia 6, 1
- Shock states (cardiogenic, distributive, or hypovolemic) 2
- Severe infection or conditions causing tissue hypoxia 6
- Liver dysfunction or failure 6, 5
Alternative Glycemic Management in the ICU
Insulin is the preferred treatment for hyperglycemia in critically ill patients:
- Continuous insulin infusion is recommended for critically ill patients in the ICU 6
- Transition to subcutaneous basal-bolus insulin regimens once patients stabilize and approach ICU discharge 6
- Target glucose range of 70-180 mg/dL (avoiding both hyperglycemia >200 mg/dL and hypoglycemia <90 mg/dL) 6, 7
For non-critically ill hospitalized patients with mild-to-moderate hyperglycemia, basal insulin with correction doses may be appropriate, but metformin remains contraindicated if any of the above risk factors are present 6.
Critical Clinical Pitfalls
- Do not continue metformin simply because the patient is taking oral intake—oral intake status is irrelevant when ICU-level risk factors for MALA are present 1
- Do not wait for lactate elevation to discontinue metformin—prevention requires stopping the drug before lactic acidosis develops 1, 2
- Do not restart metformin at ICU discharge until acute conditions have fully resolved and renal function has been reassessed 1
Monitoring Requirements During ICU Stay
- Measure lactate concentrations in fragile patients, particularly if metformin was recently taken 1
- Monitor for early MALA symptoms including nonspecific gastrointestinal complaints, dyspnea, generalized weakness, and myalgias 2
- Check arterial blood gas if lactate >2 mmol/L or pH <7.35 develops 2
Criteria for Restarting Metformin Post-ICU
Metformin should only be restarted after hospital discharge when:
- All acute conditions that increase lactic acidosis risk have completely resolved 1
- Renal function has been reassessed and eGFR is ≥30 mL/min/1.73 m² (consider dose reduction if eGFR 30-45 mL/min/1.73 m²) 1, 4
- No ongoing sepsis, shock, or organ dysfunction is present 1, 2
- Patient education has been provided about discontinuing metformin during future acute illnesses 2