SITAGLIPTIN PHOSPHATE AND METFORMIN HYDROCHLORIDE
Clinical safety rating: safe
No significant drug interactions May cause hypersensitivity reactions including anaphylaxis.
Sitagliptin inhibits dipeptidyl peptidase-4 (DPP-4), increasing endogenous incretin hormones (GLP-1, GIP) which enhance insulin secretion and decrease glucagon levels in a glucose-dependent manner. Metformin activates AMP-activated protein kinase (AMPK), decreasing hepatic glucose production and improving insulin sensitivity.
| Metabolism | Sitagliptin: primarily excreted unchanged in urine (metabolism minor, CYP3A4 and CYP2C8 involved). Metformin: not metabolized, excreted unchanged in urine. |
| Excretion | Sitagliptin: 87% renal excretion as unchanged drug, 13% fecal (biliary). Metformin: 90% renal excretion as unchanged drug, 10% fecal. |
| Half-life | Sitagliptin: terminal t1/2 12.4 hours, allows once-daily dosing. Metformin: terminal t1/2 6.2 hours, accumulates with renal impairment. |
| Protein binding | Sitagliptin: 38% bound to plasma proteins. Metformin: negligible protein binding (<1%). |
| Volume of Distribution | Sitagliptin: Vd approximately 198 L (2.8 L/kg in 70 kg). Metformin: Vd 654±358 L (9.3 L/kg), high tissue distribution. |
| Bioavailability | Sitagliptin: oral bioavailability 87%. Metformin: absolute oral bioavailability 50-60% (decreased at higher doses). |
| Onset of Action | Oral: Sitagliptin inhibits DPP-4 within 1 hour, peak glucose lowering at 2-4 hours. Metformin reduces fasting glucose within 1-2 days, maximal effect in 1-2 weeks. |
| Duration of Action | Sitagliptin 24-hour DPP-4 inhibition supports once-daily dosing. Metformin duration 12-24 hours, requires twice-daily or extended-release formulations. |
Initial dose based on current metformin dose: for patients not on metformin, start with sitagliptin 50 mg/metformin 500 mg PO BID; for metformin monotherapy, switch to sitagliptin 50 mg/metformin 500 mg or 1000 mg PO BID; for patients on sitagliptin, start with sitagliptin 50 mg/metformin 500 mg or 1000 mg PO BID. Maximum daily dose: sitagliptin 100 mg, metformin 2000 mg.
| Dosage form | TABLET |
| Renal impairment | eGFR 30-45 mL/min/1.73m2: maximum sitagliptin 50 mg/metformin 1000 mg daily (administer as sitagliptin 50 mg/metformin 500 mg BID or sitagliptin 50 mg/metformin 1000 mg daily); eGFR <30 mL/min/1.73m2: contraindicated. |
| Liver impairment | Avoid use in patients with hepatic impairment due to metformin component. Contraindicated in Child-Pugh Class C; use with caution and consider dose reduction in Child-Pugh Class A or B (metformin associated with lactic acidosis risk). |
| Pediatric use | Approved for type 2 diabetes in patients ≥10 years old; typical starting dose: sitagliptin 50 mg/metformin 500 mg PO BID, titrate based on glycemic control; maximum daily dose: sitagliptin 100 mg, metformin 2000 mg. |
| Geriatric use | Start with lower doses (e.g., sitagliptin 25 mg/metformin 500 mg daily) due to age-related renal function decline; monitor renal function closely; contraindicated if eGFR <45 mL/min/1.73m2. |
| 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 is excreted into breast milk in low concentrations (M/P ratio ~0.35-0.4). Sitagliptin is excreted in animal milk; unknown in humans. Both drugs are considered compatible with breastfeeding based on limited data; monitor infant for hypoglycemia if metformin used. |
| Teratogenic Risk | Sitagliptin/metformin is FDA Pregnancy Category B. Metformin is not teratogenic in animal studies; limited human data show no increased risk of major malformations. Sitagliptin: animal studies show no teratogenicity at high doses; no adequate human studies. First trimester: no increased risk of major birth defects seen in observational metformin studies. Second/third trimester: metformin crosses placenta; minimal data for sitagliptin. Risk of neonatal hypoglycemia with metformin if used near delivery. |
■ FDA Black Box Warning
Lactic acidosis due to metformin accumulation, especially in patients with renal impairment, acute decompensation, or hypoxic states.
| Common Effects | Nasopharyngitis |
| Serious Effects |
["Severe renal impairment (eGFR < 30 mL/min/1.73 m²)","Acute or chronic metabolic acidosis (including diabetic ketoacidosis)","History of serious hypersensitivity reaction to sitagliptin or metformin","Concurrent use of iodinated contrast media (temporarily discontinue)"]
| Precautions | ["Lactic acidosis risk (renal impairment, acute CHF, sepsis, dehydration, hepatic impairment, alcohol abuse)","Pancreatitis (discontinue if suspected)","Heart failure risk with DPP-4 inhibitors","Hypoglycemia when used with sulfonylureas or insulin","Renal function monitoring prior to initiation and periodically","Vitamin B12 deficiency with long-term metformin use"] |
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| Fetal Monitoring | Monitor blood glucose, HbA1c, renal function (serum creatinine, eGFR) at baseline and periodically. Fetal monitoring: growth ultrasound, amniotic fluid index, fetal surveillance if poor glycemic control or comorbidities. Monitor for lactic acidosis (metformin) if renal impairment or hypoxia. |
| Fertility Effects | No known significant effects on fertility in humans. Metformin may improve ovulatory function in women with PCOS. Sitagliptin: no known fertility impairment in animal studies. |