FORTAMET

Clinical safety rating: caution

Comprehensive clinical and safety monograph for FORTAMET (FORTAMET).

How it works

Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization.

What the body does with it

Metabolism	Not metabolized; excreted unchanged in urine (90% via renal tubules).
Excretion	Renal excretion of unchanged drug accounts for approximately 90% of elimination; the remainder is excreted fecally (via bile).
Half-life	Terminal elimination half-life is approximately 6.2 hours (range 4–9 hours) in patients with normal renal function; half-life is prolonged in renal impairment (up to 18 hours in moderate impairment and 24 hours in severe impairment).
Protein binding	Negligible; less than 5% bound to plasma proteins.
Volume of Distribution	Apparent volume of distribution is 654 L (9.3 L/kg for a 70 kg individual), indicating extensive tissue distribution.
Bioavailability	Absolute oral bioavailability is approximately 50–60% for immediate-release formulations; for FORTAMET extended-release, bioavailability is 50% relative to immediate-release, with food slightly increasing absorption.
Onset of Action	Following oral administration, the reduction in plasma glucose begins within 30 minutes, with peak effect at approximately 2 hours.
Duration of Action	Duration of glucose-lowering effect is 8–12 hours for immediate-release formulations; for extended-release (FORTAMET), the effect lasts up to 24 hours, allowing once-daily dosing.

Classification & Brands

Dosing & administration

Initial: 500 mg orally twice daily or 1000 mg orally once daily; titrate in increments of 500 mg weekly; maximum daily dose: 2000 mg.

Dosage form	TABLET, EXTENDED RELEASE
Renal impairment	eGFR 45-60 mL/min: reduce dose or consider discontinuation; eGFR <45 mL/min: contraindicated.
Liver impairment	Contraindicated in severe hepatic impairment (Child-Pugh class C); use caution in moderate impairment (Child-Pugh class B).
Pediatric use	Not recommended for pediatric patients (safety and efficacy not established).
Geriatric use	Start at lowest dose; avoid maximum doses; monitor renal function closely due to age-related decline.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for FORTAMET (FORTAMET).

Breastfeeding	Metformin is excreted into breast milk. The M/P ratio is approximately 0.35-0.5. Infant exposure is estimated to be about 0.5-1% of the maternal weight-adjusted dose. No adverse effects in breastfed infants have been reported. Use with caution, especially in premature or ill infants.
Teratogenic Risk	FORTAMET (metformin) is FDA Pregnancy Category B. No increased risk of major malformations or spontaneous abortion has been observed in first trimester exposure. Second and third trimester exposure may be associated with lower birth weight but not with congenital anomalies. However, uncontrolled maternal diabetes poses greater fetal risk. Metformin crosses the placenta.

Warnings & precautions

■ FDA Black Box Warning

Lactic acidosis: rare but serious, fatal in ~50% of cases. Risk increases with renal impairment, age ≥65, hepatic impairment, acute HF, dehydration, excessive alcohol, use of iodinated contrast, surgery, or hypoxia. Discontinue if acidosis suspected.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Renal impairment (eGFR <30 mL/min/1.73 m²)","Acute or chronic metabolic acidosis including diabetic ketoacidosis","Hypersensitivity to metformin","Severe hepatic impairment","Acute conditions with risk of lactic acidosis (e.g., acute HF, sepsis, dehydration)"]

Clinical Precautions

Precautions

["Lactic acidosis risk","Hypoglycemia when used with insulin or sulfonylureas","Vitamin B12 deficiency with long-term use","Acute kidney injury","Cardiovascular collapse in elderly or debilitated patients"]

Clinical Tips & Counseling

Drug interactions

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FORTAMET

Clinical safety rating: caution

Comprehensive clinical and safety monograph for FORTAMET (FORTAMET).

How it works

Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization.

What the body does with it

Metabolism	Not metabolized; excreted unchanged in urine (90% via renal tubules).
Excretion	Renal excretion of unchanged drug accounts for approximately 90% of elimination; the remainder is excreted fecally (via bile).
Half-life	Terminal elimination half-life is approximately 6.2 hours (range 4–9 hours) in patients with normal renal function; half-life is prolonged in renal impairment (up to 18 hours in moderate impairment and 24 hours in severe impairment).
Protein binding	Negligible; less than 5% bound to plasma proteins.
Volume of Distribution	Apparent volume of distribution is 654 L (9.3 L/kg for a 70 kg individual), indicating extensive tissue distribution.
Bioavailability	Absolute oral bioavailability is approximately 50–60% for immediate-release formulations; for FORTAMET extended-release, bioavailability is 50% relative to immediate-release, with food slightly increasing absorption.
Onset of Action	Following oral administration, the reduction in plasma glucose begins within 30 minutes, with peak effect at approximately 2 hours.
Duration of Action	Duration of glucose-lowering effect is 8–12 hours for immediate-release formulations; for extended-release (FORTAMET), the effect lasts up to 24 hours, allowing once-daily dosing.

Classification & Brands

Dosing & administration

Initial: 500 mg orally twice daily or 1000 mg orally once daily; titrate in increments of 500 mg weekly; maximum daily dose: 2000 mg.

Dosage form	TABLET, EXTENDED RELEASE
Renal impairment	eGFR 45-60 mL/min: reduce dose or consider discontinuation; eGFR <45 mL/min: contraindicated.
Liver impairment	Contraindicated in severe hepatic impairment (Child-Pugh class C); use caution in moderate impairment (Child-Pugh class B).
Pediatric use	Not recommended for pediatric patients (safety and efficacy not established).
Geriatric use	Start at lowest dose; avoid maximum doses; monitor renal function closely due to age-related decline.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for FORTAMET (FORTAMET).

Breastfeeding	Metformin is excreted into breast milk. The M/P ratio is approximately 0.35-0.5. Infant exposure is estimated to be about 0.5-1% of the maternal weight-adjusted dose. No adverse effects in breastfed infants have been reported. Use with caution, especially in premature or ill infants.
Teratogenic Risk	FORTAMET (metformin) is FDA Pregnancy Category B. No increased risk of major malformations or spontaneous abortion has been observed in first trimester exposure. Second and third trimester exposure may be associated with lower birth weight but not with congenital anomalies. However, uncontrolled maternal diabetes poses greater fetal risk. Metformin crosses the placenta.