RIOMET ER
Clinical safety rating: caution
Comprehensive clinical and safety monograph for RIOMET ER (RIOMET ER).
Biguanide that decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization.
| Metabolism | Not metabolized by the liver; excreted unchanged in urine via tubular secretion. No significant hepatic metabolism; no cytochrome P450 involvement. |
| Excretion | Renal elimination of unchanged drug accounts for approximately 90% of an absorbed dose; fecal excretion is minimal (<5%). |
| Half-life | Terminal elimination half-life is approximately 6.2 hours in patients with normal renal function; prolonged to up to 17.6 hours in renal impairment (eGFR <30 mL/min). |
| Protein binding | Negligible protein binding (metformin does not bind to plasma proteins). |
| Volume of Distribution | Apparent volume of distribution is 654 ± 358 L (approximately 9.3 L/kg for a 70 kg individual); indicates extensive tissue distribution. |
| Bioavailability | Bioavailability of RIOMET ER is approximately 50-60% relative to immediate-release metformin; food increases the extent of absorption (AUC) by about 70%. |
| Onset of Action | Peak plasma concentrations are reached 7-8 hours post-dose (extended-release formulation); antihyperglycemic effect begins within the first week of dosing. |
| Duration of Action | Duration of glucose-lowering effect is approximately 24 hours with once-daily dosing; sustained suppression of hepatic glucose production persists for the dosing interval. |
| Molecular Weight | 165.62 |
Oral, 500 mg once daily, increase by 500 mg weekly to maximum 2000 mg once daily.
| Dosage form | FOR SUSPENSION, EXTENDED RELEASE |
| Renal impairment | eGFR 30-60 mL/min: reduce dose by 50%; eGFR <30 mL/min: contraindicated. |
| Liver impairment | Child-Pugh Class B: avoid use; Class C: contraindicated. |
| Pediatric use | Not indicated for pediatric patients (safety and efficacy not established). |
| Geriatric use | Start at 500 mg once daily; titrate slowly; monitor renal function; avoid if eGFR <30 mL/min. |
| 1st trimester | Metformin crosses the placenta. Limited human data do not show an increased risk of major birth defects. However, insulin is preferred for gestational diabetes and pregestational diabetes due to more extensive safety data. |
| 2nd trimester | May be used in gestational diabetes when insulin is not feasible. Monitor fetal growth due to potential for fetal hypoglycemia and macrosomia. |
| 3rd trimester | Avoid near term due to risk of neonatal hypoglycemia and lactic acidosis; consider switch to insulin. |
Clinical note
Comprehensive clinical and safety monograph for RIOMET ER (RIOMET ER).
| Placental transfer | Metformin crosses the placenta with cord blood levels similar to maternal levels, indicating complete transfer. |
| Breastfeeding | Metformin is excreted into breast milk in small amounts. The relative infant dose is estimated to be 0.5-2% of the maternal weight-adjusted dose. No adverse effects have been reported in breastfed infants. Compatible with breastfeeding, but monitor infant for signs of hypoglycemia or gastrointestinal effects. |
■ FDA Black Box Warning
Lactic acidosis: Rare but serious metabolic complication; risk increases with conditions such as renal impairment, concomitant use of certain drugs, advanced age, hypoxic states, and hepatic impairment. Discontinue if suspected and monitor lactate levels.
| Serious Effects |
Hypersensitivity to metforminSevere renal impairment (eGFR <30 mL/min/1.73 m²)Acute or chronic metabolic acidosis, including diabetic ketoacidosisAcute or severe heart failureHepatic impairmentHistory of lactic acidosisUse of intravenous iodinated contrast media (temporary discontinuation required)
| Precautions | Lactic acidosis risk: Avoid in renal impairment (eGFR < 30 mL/min/1.73 m²), acute or chronic metabolic acidosis, or hypoxic conditions., Impaired renal function: Monitor renal function before initiation and periodically., Radiologic studies with iodinated contrast: Temporarily discontinue metformin at the time of or prior to procedure in patients with eGFR 30–60 mL/min/1.73 m² or with hepatic impairment, alcoholism, or unstable cardiac status; recheck eGFR 48 hours after procedure and restart if stable., Hypoxic states: Increased risk of lactic acidosis in conditions like congestive heart failure, acute myocardial infarction, sepsis., Hepatic impairment: Avoid in patients with clinical or laboratory evidence of hepatic disease., Alcohol intake: Warn against excessive acute or chronic alcohol use., Vitamin B12 deficiency: Monitor hematologic parameters annually; metformin can decrease B12 levels., Drug interactions: Concomitant use with carbonic anhydrase inhibitors may increase risk of lactic acidosis. |
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| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Metformin (RIOMET ER) is generally considered low risk for teratogenicity. Available data do not indicate an increased risk of major congenital anomalies with first-trimester exposure. However, uncontrolled gestational diabetes carries significant fetal risks, so metformin may be used if insulin is not an option. |
| Fetal Monitoring | Monitor maternal renal function, liver function, and vitamin B12 levels periodically. In pregnancy, monitor glycemic control closely, fetal growth and well-being via ultrasound and nonstress tests as indicated. Assess for signs of lactic acidosis if renal impairment develops. |
| Fertility Effects | Metformin may improve ovulation and fertility in women with polycystic ovary syndrome (PCOS) by reducing insulin resistance. No adverse effects on fertility in males or females beyond therapeutic effects. |
| Food/Dietary | Alcohol: increased risk of lactic acidosis; avoid excessive intake. Grapefruit: no significant interaction reported. Metformin does not require specific food restrictions, but taking with food reduces GI upset. Avoid high-fat meals that may affect absorption of extended-release formulation. |
| Clinical Pearls | RIOMET ER (metformin ER) is indicated for type 2 diabetes. It requires gradual dose titration to minimize GI side effects. Avoid in eGFR <30 mL/min/1.73 m²; assess renal function before initiation and annually. Discontinue with use of iodinated contrast if eGFR <60 mL/min/1.73 m², and hold for 48 hours post-procedure. Lactic acidosis risk is rare but serious; watch for hypoxic states. Monitor vitamin B12 levels annually due to potential deficiency. Extended-release formulation allows once-daily dosing, improving adherence. |
| Patient Advice | Take with the largest meal of the day to reduce stomach upset. · Swallow tablet whole; do not crush, chew, or cut. · Avoid alcohol while taking this medication to prevent lactic acidosis. · Report symptoms of lactic acidosis immediately: unusual muscle pain, difficulty breathing, severe drowsiness, feeling cold, slow heartbeat. · Monitor blood sugar regularly as directed. · You may experience a metallic taste or diarrhea initially; these often improve over time. · Do not skip doses; if you miss a dose, take it as soon as you remember unless almost time for next dose; do not double. · Inform your doctor about all medications, especially carbonic anhydrase inhibitors, topiramate, and contrast dye procedures. |