Metformin

Biguanide·Endocrinology - Oral Antidiabetics

Type 2 Diabetes Mellitus

PBSORALDiabex, Diaformin, Formet1000 mg tabletS4+1

Max Dose

3 g/day

Half-life

6.5 h

Lactic Acidosis

CRITICAL

eGFR < 30

CONTRAIND.

Rapid Summary

Overview

The absolute foundational first-line therapy for Type 2 Diabetes. Enhances insulin sensitivity and suppresses hepatic glucose output without causing weight gain.

Maximum Dose

Max 3 g/day (though benefit plateaus at 2 g/day).

Clinical Focus

Highly toxic if accumulated. Must be withheld in acute kidney injury, severe hypoxia, or sepsis due to risk of fatal lactic acidosis.

Bottom Line

Metformin is the undisputed first-line oral hypoglycaemic for type 2 diabetes with cardiovascular benefit, but must be withheld before contrast and in acute kidney injury due to lactic acidosis risk.

Formulation & Access

Brand Names

Diabex, Diaformin, Formet

Oral Routes

Immediate Release (IR) Tablets (500, 850, 1000 mg). Extended Release (XR) Tablets (500, 1000 mg).

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Type 2 Diabetes Mellitus.

Off-Label

OFF

PCOS (improves ovulation), metabolic syndrome.

Clinical Place

First-line agent. Zero risk of hypoglycemia when used alone.

Quick reference

Class & Role

Biguanide — The absolute foundational first-line therapy for Type 2 Diabetes.

Route / Formulation

Immediate Release (IR) Tablets (500, 850, 1000 mg). Extended Release (XR) Tablets (500, 1000 mg). (Diabex, Diaformin, Formet)

Usual Dose & Max

PO 500 mg OD or BD with meals. Titrate slowly to 1000 mg BD. Max 3 g/day (though benefit plateaus at 2 g/day).

Key Indication Doses

Type 2 Diabetes (IR): PO 500 mg OD or BD with meals. Titrate slowly to 1000 mg BD. Type 2 Diabetes (XR): PO 500-2000 mg OD with the evening meal. Renal Impairment: Max 1000 mg/day if eGFR 30-45. Cease entirely if eGFR < 30.

Best Uses

Metformin is the undisputed first-line oral hypoglycaemic for type 2 diabetes with cardiovascular benefit, but must be withheld before contrast and in acute kidney injury due to lactic acidosis risk.

Avoid / Cautions

Severe renal impairment (eGFR < 30), severe tissue hypoxia (acute MI, acute decompensated heart failure, severe sepsis), acute severe liver disease. Pregnancy Category C, but widely used and safe in gestational diabetes.

Key Risks

Metabolic: Metformin-Associated Lactic Acidosis (MALA). High mortality rate. Occurs when drug accumulates (renal failure) or tissues are starved of oxygen (sepsis, heart failure). Gastrointestinal: Nausea, diarrhea, abdominal cramping (extremely common, affects up to 30%, usually transient). Haematological: Vitamin B12 malabsorption with long-term use.

Key Interactions

IV Contrast Dye. Contrast can cause acute kidney injury. If a patient on metformin gets contrast-induced AKI, the metformin will accumulate and cause fatal lactic acidosis. Withhold metformin for 48 hours post-contrast if eGFR is borderline. Alcohol (increases risk of lactic acidosis).

Monitoring

Baseline and 6-monthly eGFR. Annual B12 levels. Routine HbA1c. 'Sick Day Rules': Instruct patients to withhold Metformin if they develop gastroenteritis (dehydration) to prevent acute renal failure and MALA.

Clinical Pearl

If a patient cannot tolerate the explosive diarrhea from standard Metformin IR, switch them to the Extended Release (XR) version taken with dinner. It bypasses upper GI rapid absorption and cures the nausea/diarrhea in 90% of cases.

Access

Diabex, Diaformin, Formet1000 mg tablet

Brand: Diabex, Diaformin, Formet
Formulation: Immediate Release (IR) Tablets (500, 850, 1000 mg)

Metformin

Biguanide·Endocrinology - Oral Antidiabetics

Type 2 Diabetes Mellitus

PBSORALDiabex, Diaformin, Formet1000 mg tabletS4+1

Max Dose

3 g/day

Half-life

6.5 h

Lactic Acidosis

CRITICAL

eGFR < 30

CONTRAIND.

Rapid Summary

Overview

The absolute foundational first-line therapy for Type 2 Diabetes. Enhances insulin sensitivity and suppresses hepatic glucose output without causing weight gain.

Maximum Dose

Max 3 g/day (though benefit plateaus at 2 g/day).

Clinical Focus

Highly toxic if accumulated. Must be withheld in acute kidney injury, severe hypoxia, or sepsis due to risk of fatal lactic acidosis.

Bottom Line

Metformin is the undisputed first-line oral hypoglycaemic for type 2 diabetes with cardiovascular benefit, but must be withheld before contrast and in acute kidney injury due to lactic acidosis risk.

Formulation & Access

Brand Names

Diabex, Diaformin, Formet

Oral Routes

Immediate Release (IR) Tablets (500, 850, 1000 mg). Extended Release (XR) Tablets (500, 1000 mg).

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Type 2 Diabetes Mellitus.

Off-Label

OFF

PCOS (improves ovulation), metabolic syndrome.

Clinical Place

First-line agent. Zero risk of hypoglycemia when used alone.

Quick reference

Class & Role

Biguanide — The absolute foundational first-line therapy for Type 2 Diabetes.

Route / Formulation

Immediate Release (IR) Tablets (500, 850, 1000 mg). Extended Release (XR) Tablets (500, 1000 mg). (Diabex, Diaformin, Formet)

Usual Dose & Max

PO 500 mg OD or BD with meals. Titrate slowly to 1000 mg BD. Max 3 g/day (though benefit plateaus at 2 g/day).

Key Indication Doses

Best Uses

Metformin is the undisputed first-line oral hypoglycaemic for type 2 diabetes with cardiovascular benefit, but must be withheld before contrast and in acute kidney injury due to lactic acidosis risk.

Avoid / Cautions

Key Risks

Key Interactions

Monitoring

Clinical Pearl

Access

Diabex, Diaformin, Formet1000 mg tablet

Brand: Diabex, Diaformin, Formet
Formulation: Immediate Release (IR) Tablets (500, 850, 1000 mg)