Elderly patients have an increased susceptibility to burns and a substantial mortality that has not significantly changed over the last three decades. Elderly burn patients not only have an augmented response to burn but also express a prolonged hypermetabolic response.Glucose metabolism with insulin resistance is a hypermetabolic response pathway that profoundly affects post-burn outcomes. The aim if this study is to determine whether metformin can improve morbidity and mortality in elderly burn patients. The investigators hypothesize that metformin will improve clinical outcomes and mortality of elderly burn patients by alleviating the complex inflammatory and hypermetabolic responses after burn.

Inclusion Criteria:

1. Aged 60 - 99 years of age.
2. ≥5% total body surface area (TBSA) burn.
3. Admitted to burn center ≤ 120 hours post-burn injury.
4. At least one surgical intervention likely required.
5. Provide written informed consent.

Exclusion Criteria:

1. Death upon admission.
2. Decision not to treat due to burn injury severity.
3. Presence of anoxic brain injury that is not expected to result in complete recovery.
4. Pre-existing renal failure (eGFR is < 30 mL/min).
5. Severe liver disease (Child-Pugh C).
6. Pre-existing insulin-dependent type II diabetes.
7. Clinical contraindication to give metformin.
8. Allergy to metformin or insulin.
9. History of lactic acidosis while receiving metformin treatment.