1. Clinical Overview
A fixed-dose combination (FDC) oral antidiabetic medication containing Sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, and Metformin, a biguanide. This combination provides complementary mechanisms of action to improve glycemic control in adults with type 2 diabetes mellitus (T2DM) by increasing incretin levels (GLP-1 and GIP) to stimulate glucose-dependent insulin release and suppress glucagon secretion, while simultaneously decreasing hepatic glucose production and improving insulin sensitivity. It is indicated when treatment with metformin alone does not provide adequate glycemic control.
| Onset | Duration | Bioavailability |
|---|---|---|
| Sitagliptin: Plasma concentration peaks in 1-4 hours. Metformin: Plasma concentration peaks in approximately 2.5 hours. Therapeutic glucose-lowering effect begins within days. | Sitagliptin: Pharmacodynamic effect (DPP-4 inhibition >80%) lasts 24 hours, supporting once-daily dosing. Metformin: Plasma half-life is about 6.5 hours, but its glucose-lowering effect is prolonged, requiring twice-daily administration of this combination. | Sitagliptin: Approximately 87%. Metformin: 50-60%. Bioavailability of Metformin is reduced when taken with food. |
2. Mechanism of Action
The combination exerts a synergistic glucose-lowering effect through two distinct pathways. Sitagliptin inhibits the enzyme DPP-4, thereby increasing the concentrations of active incretin hormones (GLP-1 and GIP). This enhances glucose-dependent insulin secretion from pancreatic beta cells and suppresses glucagon secretion from alpha cells. Metformin decreases hepatic gluconeogenesis and glycogenolysis, improves peripheral glucose uptake and utilization, and may have a mild anorectic effect.
3. Indications & Uses
- Management of type 2 diabetes mellitus in adults as an adjunct to diet and exercise.
- Indicated when metformin monotherapy does not provide adequate glycemic control.
4. Dosage & Administration
Adult Dosage: One tablet twice daily, with meals (typically breakfast and dinner). The maximum recommended daily dose is Sitagliptin 100mg + Metformin 2000mg.
Administration: Swallow whole with a glass of water. Must be taken with or immediately after meals to reduce gastrointestinal upset from metformin. Do not crush or chew.
5. Side Effects
Common side effects may include:
- Nausea
- Diarrhea
- Abdominal discomfort
- Flatulence
- Headache
- Upper respiratory tract infection
- Hypoglycemia (when used with sulfonylureas or insulin)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Cimetidine | Increases metformin plasma concentration by competing for renal tubular secretion. | Moderate |
| Carbonic Anhydrase Inhibitors (e.g., Topiramate, Acetazolamide) | May increase risk of lactic acidosis. | Major |
| Iodinated Contrast Media | Risk of acute renal failure and lactic acidosis. Metformin should be withheld before and after procedure. | Major |
| Alcohol | Potentiates metformin's effect on lactate metabolism; increases risk of lactic acidosis and hypoglycemia. | Major |
| Sulfonylureas (e.g., Glimepiride) or Insulin | Increased risk of hypoglycemia. May require dose reduction of sulfonylurea/insulin. | Moderate |
| Digoxin | Metformin may increase digoxin concentration. | Moderate |
| Diuretics (especially loop diuretics) | May affect renal function and increase metformin levels/risk. | Moderate |
| Corticosteroids | May lead to loss of glycemic control, requiring dose adjustment. | Moderate |
7. Patient Counselling
- DO take the tablet twice daily with meals.
- DO monitor your blood glucose levels as advised by your doctor.
- DO maintain a regular diet and exercise schedule.
- DO inform all your doctors and your pharmacist that you are taking this medicine.
- DO get your kidney function tested regularly.
- DONT take this medicine if you are pregnant, planning pregnancy, or breastfeeding without consulting your doctor.
- DONT skip meals.
- DONT consume excessive alcohol.
- DONT take this medicine around the time of an X-ray/scan using iodinated contrast dye without informing your doctor.
8. Toxicology & Storage
Overdose: Sitagliptin: Doses up to 800mg were well tolerated. Expected: Hypoglycemia (if combined with other agents), headache, GI disturbances. Metformin Overdose: Hypoglycemia (rare alone), severe lactic acidosis (primary concern) presenting with vomiting, diarrhea, abdominal pain, hypothermia, hypotension, and respiratory distress.
Storage: Store below 30°C. Protect from light and moisture. Keep the container tightly closed. Keep out of reach of children. Do not use after the expiry date printed on the pack.