Pharmacy Diabetes

B-2.2 Biguanides_Metformin-formulations imediate release

Name of Medicine
Metformin Hydrochloride Immediate Release
  • Immediate release tablets in 500mg, 850mg and 1000mg strengths.
  • Care should be taken not to crush or chew the tablets.
  • Tablets should be taken in divided doses throughout the day, with meals.
Key Practice Points
Therapeutic Indications:
  • Metformin is indicated in the treatment of type 2 diabetes mellitus in adults, children from 10 years of age and adolescents, particularly in overweight individuals, when dietary management and physical activity alone does not result in adequate glycaemic management.
  • For adults, metformin may be used as initial treatment or when sulfonylurea has not been adequate either alone or in combination with a sulfonylurea and other oral agents or as adjuvant therapy in insulin requiring type 2 diabetes
For the most up to date PBS therapeutic indications for metformin, please see
  • Initially 500mg should be taken once or twice a day and the dose increased gradually over one to two weeks.
  • A slow increase in dose may improve the renown gastrointestinal side effects. Maximum dose for the immediate release metformin is 3000 mg daily.
  • The action of metformin continues to reach its peak over approximately 21 days.
  • Renal insufficiency: As metformin hydrochloride is excreted by the kidney, it is recommended that creatinine clearance and/or serum creatinine levels be determined before initiating treatment and regularly thereafter. At least annually in those individuals with normal renal function. At least two to four times a year in those with serum creatinine levels at the upper limit of normal and in the elderly. Dosage adjustments of metformin should occur as follows. – CrCl 60-90 mL/min/1.73 m maximum dose of metformin 2 gm a day – CrCL 30-60 mL/ min/1.73 m maximum dose of metformin 1gm per day – CrCL , 30 mL min/1.73 m metformin should be ceased
  • Hepatic insufficiency: Metformin should not be used in hepatic dysfunction de to the increased risk of lactic acidosis.
  • Initial and maintenance dosing should always be individualized based on both renal and liver function. Due to the potential of changes in renal function, the dose should be adjusted based on renal function, with regular reviews undertaken.
  • Lactic acidosis. Life threatening lactic acidosis can occur due to metformin accumulating in susceptible individuals. Early warning symptoms include anorexia, nausea, vomiting, abdominal pain and cramps.. Risks factors include renal dysfunction, old age, and doses of metformin >2g daily. It can also be associated with prolonged fasting, excessive alcohol, and hepatic dysfunction. Diabetes Medscheck counselling side effect profile
  • Surgery: Discontinue metformin 48 hours before surgery, if possible. It is common practice not to restart metformin for 2 days after surgery and once the individual is eating and drinking normally. Diabetes Medscheck side effect profile
  • Kidney Function: Metformin is entirely renally excreted by the kidney and will accumulate with renal insufficiency. Check creatinine clearance and/or serum creatinine levels before starting treatment and regularly thereafter (annually for those individuals with normal renal function). Renal function should be checked at least two to four times a year for those whose serum creatinine levels are at the upper limit of normal and for elderly individuals. Current recommendations for metformin are CrCl 60-90 mL/min dose of metformin 2g daily, 30-60 mL/minute 1g daily. Metformin should be ceased if eGFR falls below 30 mL/min/1.73m. Diabetes Medscheck referral to health care professional for annual cycle of care
Adverse Effects:
  • Gastrointestinal- diarrhoea, nausea, vomiting, abdominal pain, and loss of appetite. Starting with a low dose and increasing slowly can help with these side effects. Taking medicine with meals can also reduce the unwanted effects. Altered taste is also commonly reported with metformin. Reduced vitamin B12 absorption. Please see clinical interventions for further information.
  • Dermatological -skin reactions including urticaria, erythema, and pruritus.
  • Lactic acidosis
  • Isolated reports of liver function test abnormalities or hepatitis. These often resolve after the Metformin is ceased.
  • Hypersensitivity to Metformin or any of the excipients.
  • Renal dysfunction or any acute condition that has the potential to lower renal function (dehydration, severe infection, shock, contrast dye).
  • Ketoacidosis due to diabetes
  • Renal failure or renal dysfunction.
  • Any acute condition that has the potential to lower renal function (dehydration, severe infection, shock, contrast dye).
  • Major surgery.
  • Severe hepatic dysfunction.
  • Acute or chronic disease that can cause tissue hypoxia (cardiac failure, MI, pancreatitis, sepsis).
Pharmacokinetic Properties - Summary

Metformin is absorbed through the entire gastrointestinal mucosa. Studies have shown there is a lack of dose proportionally with increasing doses thought to be due to a reduction of absorption. It is therefore thought that metformin absorption is saturable and incomplete. 


Plasma protein binding of metformin is negligible.

Renal clearance of metformin is > 400 mL/min, indicating that metformin is eliminated by glomerular filtration and tubular secretion. Dosage adjustment should therefore occur in those with renal dysfunction and ceased in renal failure.  For more detailed information on this product please consult the product information. 
More Information

For more detailed information on this product please consult the product information.