JANUMET XR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for JANUMET XR (JANUMET XR).
JANUMET XR is a combination of sitagliptin, a DPP-4 inhibitor, and metformin, a biguanide. Sitagliptin increases active incretin levels (GLP-1, GIP), enhancing glucose-dependent insulin secretion and reducing glucagon secretion. Metformin decreases hepatic glucose production, reduces intestinal glucose absorption, and improves insulin sensitivity.
| Metabolism | Sitagliptin: primarily renal excretion (70-80% unchanged), minimal hepatic metabolism via CYP3A4 and CYP2C8. Metformin: excreted unchanged in urine; no hepatic metabolism. |
| Excretion | Sitagliptin: ~79% excreted unchanged in urine via renal tubular secretion (active secretion) and glomerular filtration; ~13% undergoes hepatic metabolism; ~1% excreted in feces. Metformin: ~90% excreted unchanged in urine via active tubular secretion. |
| Half-life | Sitagliptin: terminal half-life ~12.4 hours, allowing once-daily dosing. Metformin: terminal half-life ~6.2 hours in plasma, increased to ~17.6 hours in renal impairment. |
| Protein binding | Sitagliptin: ~38% bound to plasma proteins. Metformin: negligible (<5%) protein binding. |
| Volume of Distribution | Sitagliptin: Vd ~198 L (approximately 2.8 L/kg for a 70 kg individual), indicating extensive tissue distribution. Metformin: Vd 654 ± 358 L (9.3 L/kg), widely distributed into erythrocytes and tissues. |
| Bioavailability | Sitagliptin: oral bioavailability ~87%. Metformin: oral absolute bioavailability ~50-60% for immediate-release, reduced under fed conditions; Janumet XR provides extended-release profile. |
| Onset of Action | Sitagliptin: DPP-4 inhibition reaches near-maximum within 1-2 hours. Metformin: reduction in fasting plasma glucose begins within 1-2 days; full effect by 1-2 weeks. |
| Duration of Action | Sitagliptin: DPP-4 inhibition >80% at 24 hours. Metformin: glucose-lowering effect persists for 24 hours with extended-release formulation. |
| Brand Substitutes | Sitawok M 500 Tablet, Istamet 50mg/500mg Tablet, Sitanorm M 50mg/500mg Tablet, Ignalis-M IR 50/500 Tablet, Sitaglyn M IR 50/500 Tablet, Sitamax M 50mg/1000mg Tablet, SitaOD Met 50/1000 Tablet, Siglyn M IR 50/1000 Tablet, Lupisit M 50mg/1000mg Tablet, Sitenali M 50mg/1000mg Tablet |
One tablet orally once daily, with evening meal; initial dose based on patient's current sitagliptin and metformin doses, or new patients: starting dose 50 mg sitagliptin/500 mg metformin XR; maximum dose 100 mg sitagliptin/2000 mg metformin XR per day.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | eGFR ≥45 mL/min/1.73m²: no adjustment. eGFR 30-44 mL/min/1.73m²: maximum dose 50 mg sitagliptin/1000 mg metformin XR daily. eGFR <30 mL/min/1.73m² or ESRD: contraindicated (metformin component). |
| Liver impairment | Contraindicated in patients with hepatic impairment (Child-Pugh score not specified; avoid due to metformin component risk of lactic acidosis). |
| Pediatric use | Not recommended for pediatric patients under 18 years of age due to lack of data. |
| Geriatric use | Cautious dose titration; renal function should be assessed before initiation and monitored regularly. Avoid initiation if eGFR <45 mL/min/1.73m². |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for JANUMET XR (JANUMET XR).
| Breastfeeding | Metformin is excreted in breast milk with a M/P ratio of approximately 0.35; sitagliptin is excreted in animal milk, unknown in humans. Limited data suggest low risk for full-term infants, but caution advised, especially with prematurity or renal impairment. |
| Teratogenic Risk | Janumet XR contains sitagliptin and metformin. Metformin is associated with fetal hypoxia and acidosis risk due to lactic acidosis in third trimester; limited human data show no increased major malformations. Sitagliptin: animal studies show fetal toxicity at high doses; no adequate human studies. First trimester: risk cannot be excluded; second/third trimester: avoid if possible due to metformin's effects on fetal glucose metabolism. |
■ FDA Black Box Warning
Lactic acidosis: Rare but serious risk due to metformin accumulation; risk increases with renal impairment, sepsis, dehydration, hepatic impairment, acute heart failure, and alcohol use. Discontinue if acidosis suspected.
| Serious Effects |
["Severe renal impairment (eGFR <30 mL/min/1.73m2)","Acute kidney injury or metabolic acidosis (including lactic acidosis)","History of serious hypersensitivity reaction to sitagliptin or metformin","Use during iodinated contrast imaging (temporary discontinuation)","Acute or chronic metabolic acidosis, diabetic ketoacidosis"]
| Precautions | ["Lactic acidosis risk: monitor renal function, avoid in eGFR <30 mL/min/1.73m2, hold prior to iodinated contrast procedures","Pancreatitis (sitagliptin): monitor for signs; discontinue if suspected","Acute kidney injury: monitor renal function","Hypoglycemia: may occur when combined with insulin or sulfonylureas","Vitamin B12 deficiency: metformin may reduce absorption; monitor periodically","Hypersensitivity reactions: angioedema, Stevens-Johnson syndrome reported with sitagliptin"] |
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| Fetal Monitoring | Monitor renal function, serum creatinine, and liver function tests before and during therapy. Monitor blood glucose and HbA1c. Fetal monitoring: ultrasound for growth and anomalies as per standard obstetric care. Watch for signs of lactic acidosis (maternal) and neonatal hypoglycemia. |
| Fertility Effects | Metformin may improve ovulation in women with polycystic ovary syndrome due to insulin sensitization. No known negative effects on spermatogenesis in males; sitagliptin no known adverse effects on fertility in animal studies. |