SITAGLIPTIN; METFORMIN HYDROCHLORIDE
Clinical safety rating: safe
No significant drug interactions May cause hypersensitivity reactions including anaphylaxis.
Sitagliptin is a DPP-4 inhibitor that increases incretin levels (GLP-1, GIP), enhancing glucose-dependent insulin secretion and reducing glucagon secretion. Metformin is a biguanide that decreases hepatic glucose production, decreases intestinal glucose absorption, and improves insulin sensitivity via AMP-kinase activation.
| Metabolism | Sitagliptin: primarily excreted unchanged in urine (80%), minimal hepatic metabolism via CYP3A4 and CYP2C8. Metformin: not metabolized, excreted unchanged in urine. |
| Excretion | Sitagliptin: 79% excreted unchanged in urine via renal tubular secretion and glomerular filtration; 13% metabolized with 4% excreted in feces. Metformin: 90% excreted unchanged in urine via glomerular filtration and tubular secretion; <5% in feces. |
| Half-life | Sitagliptin: terminal half-life 12.4 hours (healthy), prolonged in renal impairment (up to 28–39 hours in severe impairment). Metformin: terminal half-life 4–8.7 hours (healthy), prolonged in renal impairment (up to 17.6 hours in moderate impairment). |
| Protein binding | Sitagliptin: 38% bound to plasma proteins (primarily albumin). Metformin: negligible binding (<5% bound to plasma proteins). |
| Volume of Distribution | Sitagliptin: Vd ~198 L (approx 2.8 L/kg assuming 70 kg), indicating extensive tissue distribution. Metformin: Vd 654–750 L (approx 9.3–10.7 L/kg), indicating high tissue penetration. |
| Bioavailability | Sitagliptin: oral bioavailability 87%. Metformin: oral bioavailability 50–60% (decreased by food). |
| Onset of Action | Sitagliptin: onset 1–2 hours post-dose for DPP-4 inhibition; metformin: onset 2–3 hours post-dose for glucose-lowering effect. |
| Duration of Action | Sitagliptin: DPP-4 inhibition >24 hours; metformin: 8–12 hours for glucose-lowering effect, dosed twice daily in combination. |
1 tablet orally twice daily; each tablet contains sitagliptin 50 mg and metformin hydrochloride 500 mg, 850 mg, or 1000 mg; maximum dose: sitagliptin 100 mg/day, metformin 2000 mg/day.
| Dosage form | TABLET |
| Renal impairment | eGFR ≥45 mL/min/1.73 m2: no adjustment; eGFR 30-44: not recommended (discontinue metformin); eGFR <30: contraindicated. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B or C: not recommended (metformin contraindicated due to risk of lactic acidosis). |
| Pediatric use | Not approved for use in pediatric patients under 18 years of age. |
| Geriatric use | Start at lowest dose; monitor renal function; avoid in patients with eGFR <45 mL/min/1.73 m2; increased risk of lactic acidosis. |
| 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: excreted into breast milk in low amounts; M/P ratio ~0.4; infant dose <1% of maternal weight-adjusted dose; considered compatible. Sitagliptin: not known if excreted in human milk; animal studies show presence in milk; caution advised. Overall: limited data; benefit-risk assessment needed. |
| Teratogenic Risk | Metformin: limited human data suggest no increased risk of major birth defects; crosses placenta; consider gestational diabetes use. Sitagliptin: no adequate human data; animal studies show no teratogenicity at high doses; classified as pregnancy category B (FDA prior to 2015). Both: insufficient data for first trimester; theoretical risk of metformin-induced lactic acidosis in neonate if used near term. |
■ FDA Black Box Warning
Lactic acidosis with metformin (rare but fatal; risk increased with renal impairment, acute illness, or alcohol use).
| Common Effects | Nasopharyngitis |
| Serious Effects |
["Severe renal impairment (eGFR <30 mL/min/1.73 m²)","Metabolic acidosis (including diabetic ketoacidosis)","Acute or chronic metabolic acidosis","History of hypersensitivity to sitagliptin or metformin"]
| Precautions | ["Risk of lactic acidosis (renal impairment, age >65, liver disease, alcohol use, unstable heart failure, sepsis, surgery, contrast dye use)","Acute pancreatitis (discontinue if suspected)","Severe and disabling arthralgia","Acute renal failure","Hypoglycemia when combined with insulin or sulfonylureas","Vitamin B12 deficiency with metformin (monitor levels)"] |
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| Fetal Monitoring | Monitor maternal blood glucose, HbA1c, renal function (serum creatinine), and lactic acidosis symptoms. Fetal: ultrasound for growth and anatomy; neonatal monitoring for hypoglycemia and lactic acidosis if metformin used near delivery. |
| Fertility Effects | Metformin may improve ovulatory function in women with polycystic ovary syndrome by reducing insulin resistance. Sitagliptin: no known direct effect on fertility; animal studies showed no impairment. |