METFORMIN HYDROCHLORIDE AND SITAGLIPTIN PHOSPHATE
Clinical safety rating: safe
No significant drug interactions May cause hypersensitivity reactions including anaphylaxis.
Metformin: Activates AMP-activated protein kinase (AMPK), reducing hepatic glucose production, decreasing intestinal glucose absorption, and improving insulin sensitivity. Sitagliptin: Inhibits dipeptidyl peptidase-4 (DPP-4), increasing incretin levels (GLP-1, GIP), enhancing glucose-dependent insulin secretion and suppressing glucagon release.
| Metabolism | Metformin: Not metabolized; excreted unchanged in urine. Sitagliptin: Metabolized primarily via CYP3A4 (minor CYP2C8) to inactive metabolites; excreted renally. |
| Excretion | Metformin is excreted unchanged in urine (90% renal tubular secretion) and feces (10%). Sitagliptin is excreted primarily unchanged in urine (87% renal, 13% fecal via biliary). |
| Half-life | Metformin terminal half-life ~6.2 hours (prolonged in renal impairment; clinical context: dosing adjustment required if eGFR <45 mL/min). Sitagliptin terminal half-life ~12.4 hours (extended in renal impairment; dose adjustment for CrCl <50 mL/min). |
| Protein binding | Metformin: negligible (<5%, not bound to plasma proteins). Sitagliptin: 38% bound to plasma proteins (albumin). |
| Volume of Distribution | Metformin: Vd 1–5 L/kg (distributes into erythrocytes and tissues; clinical note: large Vd indicates extensive tissue distribution). Sitagliptin: Vd ~198 L (2.8 L/kg for 70 kg) (distribution into tissues; clinical note: moderate Vd). |
| Bioavailability | Metformin oral F ~50–60% (dose-dependent, saturable absorption) (extended-release F is ~70% of immediate-release). Sitagliptin oral F ~87% (high bioavailability). |
| Onset of Action | Metformin: onset of glucose-lowering effect within 48 hours (oral); full effect in 1–2 weeks. Sitagliptin: onset of DPP-4 inhibition within 1–2 hours (oral); clinical glycemic effect in 1–2 weeks. |
| Duration of Action | Metformin: duration of action ~24 hours (once-daily dosing); clinical note: sustained glucose reduction over 24 hours. Sitagliptin: duration of DPP-4 inhibition >24 hours (once-daily dosing); clinical note: effective for 24-hour glycemic control. |
Oral, 50 mg sitagliptin/500 mg metformin twice daily with meals. Maximum: 100 mg sitagliptin/2000 mg metformin per day in divided doses.
| Dosage form | TABLET |
| Renal impairment | GFR ≥ 45 mL/min: No adjustment. GFR 30-44 mL/min: Maximum dose 50 mg sitagliptin/1000 mg metformin per day. GFR < 30 mL/min: Contraindicated. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B or C: Not recommended. |
| Pediatric use | Not approved for pediatric use; safety and efficacy not established in patients <18 years. |
| Geriatric use | Start at low end of dosing range; assess renal function before initiation and periodically; avoid use if GFR < 45 mL/min. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
No significant drug interactions May cause hypersensitivity reactions including anaphylaxis.
| FDA category | Animal |
| Breastfeeding | Metformin: Limited human data; infant dose ~0.65% of maternal weight-adjusted dose (M/P ratio ~0.35). Sitagliptin: Not known if excreted in human milk. Caution; monitor infant for hypoglycemia. |
| Teratogenic Risk | Metformin: Not associated with major malformations in first trimester; may reduce miscarriage in PCOS. Sitagliptin: Limited human data; no major teratogenicity in animal studies at high doses. Use only if benefit outweighs potential risk. |
■ FDA Black Box Warning
Lactic acidosis: Rare but serious, especially in patients with renal impairment, hypoxia, sepsis, or hepatic impairment. Discontinue if acidosis is suspected.
| Common Effects | Nasopharyngitis |
| Serious Effects |
["Severe renal impairment (eGFR < 30 mL/min/1.73m²)","Acute or chronic metabolic acidosis, including diabetic ketoacidosis","Hypersensitivity to metformin, sitagliptin, or any components","History of pancreatitis"]
| Precautions | ["Lactic acidosis risk: caution in renal impairment, elderly, hepatic disease, alcohol use, unstable CHF, hypoxia, or surgery.","Pancreatitis: monitor for symptoms; discontinue if suspected.","Hypoglycemia: when used with insulin or sulfonylureas.","Vitamin B12 deficiency: monitor with prolonged metformin use.","Renal impairment: assess renal function before initiation and periodically; contraindicated if eGFR < 30 mL/min/1.73m².","Hypersensitivity reactions: angioedema, Stevens-Johnson syndrome, anaphylaxis."] |
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| Fetal Monitoring | Monitor renal function, liver function, and blood glucose. Fetal monitoring: growth ultrasound in third trimester due to potential for macrosomia in poorly controlled diabetes. |
| Fertility Effects | Metformin may improve ovulation in PCOS and enhance fertility. Sitagliptin: No known adverse effects on fertility. No negative impact on spermatogenesis or oogenesis. |