RIOMET
Clinical safety rating: caution
Comprehensive clinical and safety monograph for RIOMET (RIOMET).
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; excreted unchanged in urine. |
| Excretion | Renal (90% unchanged via glomerular filtration and tubular secretion); fecal (10%) |
| Half-life | Terminal elimination half-life: 6.2 hours (range 4–12 hours); clinical context: 4–5 half-lives to steady state (approx 24–36 hours); prolonged in renal impairment (e.g., creatinine clearance <60 mL/min contraindicated) |
| Protein binding | Negligible (<5%) bound to plasma proteins (albumin) |
| Volume of Distribution | 654 ± 358 L (single dose), equivalent to 9.3 L/kg (assuming 70 kg); indicates extensive tissue distribution (concentrates in erythrocytes, liver, kidney; does not bind to plasma proteins) |
| Bioavailability | Oral: 50–60% (absolute); food decreases peak concentration by 40% but extends time to peak; extent of absorption unchanged with food |
| Onset of Action | Oral: 2–4 hours to peak plasma concentration; clinical effect (glucose lowering) begins within 48 hours, maximal by 2 weeks |
| Duration of Action | Duration of glucose-lowering effect: 24 hours (once-daily dosing); clinical notes: twice-daily dosing may prolong duration in some patients; sustained release formulations provide extended duration up to 24 hours |
| Molecular Weight | 129.16 |
Oral, 500 mg twice daily or 850 mg once daily, increased gradually to 2000 mg daily in divided doses.
| Dosage form | SOLUTION |
| Renal impairment | Contraindicated if eGFR <30 mL/min/1.73m2; if eGFR 30-45, do not initiate; reduce dose by 50% if eGFR 45-60. |
| Liver impairment | Avoid use in patients with Child-Pugh Class B or C hepatic impairment; no adjustment for Class A. |
| Pediatric use | Initial: 500 mg orally twice daily for children ≥10 years; maximum 2000 mg daily. |
| Geriatric use | Start at lower doses (e.g., 500 mg once daily) due to risk of lactic acidosis; monitor renal function closely. |
| 1st trimester | Insulin is preferred; metformin may be used if insulin is not appropriate. There is no major teratogenic risk. |
| 2nd trimester | Metformin crosses the placenta; limited data show no increased risk of major malformations. |
| 3rd trimester | Metformin crosses the placenta; may be continued if benefits outweigh risks; consider monitoring for neonatal hypoglycemia. |
Clinical note
Comprehensive clinical and safety monograph for RIOMET (RIOMET).
| Placental transfer | Metformin crosses the placenta readily, achieving fetal concentrations similar to maternal concentrations. |
| Breastfeeding | Metformin is excreted into breast milk in low amounts. No adverse effects in nursing infants have been reported. The American Academy of Pediatrics considers metformin compatible with breastfeeding. Use with caution in preterm or sick infants. |
■ FDA Black Box Warning
Lactic acidosis: A rare but serious metabolic complication that can occur due to metformin accumulation; risk increases with renal impairment, sepsis, dehydration, acute heart failure, hepatic impairment, and excessive alcohol intake.
| Common Effects | Hypoglycemia low blood glucose level Headache Nausea Diarrhea Flatulence |
| Serious Effects |
Severe renal impairment (eGFR < 30 mL/min/1.73 m^2)Acute or chronic metabolic acidosis, including diabetic ketoacidosisHypersensitivity to metformin or any component of the formulation
| Precautions | Lactic acidosis risk, Renal impairment (assess renal function before initiation and periodically), Hypoglycemia risk when used with other antidiabetic agents, Vitamin B12 deficiency with long-term use, Acute heart failure, Hepatic impairment, Discontinue temporarily for IV contrast or surgery, Hypoxic states (e.g., respiratory failure, myocardial infarction) |
Loading safety data…
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Metformin (Riomet) is classified as FDA Pregnancy Category B. Available data from controlled studies in pregnant women do not show an increased risk of major birth defects. First trimester: No evidence of teratogenicity. Second and third trimesters: No fetal adverse effects observed; placental transfer occurs but at low levels. Risk of neonatal hypoglycemia is low. Use is sometimes continued in GDM if glycemic control is not achieved with insulin. |
| Fetal Monitoring | Maternal: Assess renal function (serum creatinine) prior to and during therapy, especially if at risk for lactic acidosis. Monitor blood glucose levels. Fetal: Standard antenatal monitoring including ultrasound for growth and well-being. In GDM, monitor for macrosomia, polyhydramnios. Neonatal: Observe for hypoglycemia if metformin continued to delivery. |
| Fertility Effects | Metformin may improve fertility in women with polycystic ovary syndrome (PCOS) by reducing hyperinsulinemia and restoring ovulation. No adverse effects on male or female fertility have been reported. It is not considered a fertility drug but can facilitate ovulation in anovulatory women with PCOS. |
| Food/Dietary |
| Avoid excessive alcohol consumption (especially binge drinking) as it increases the risk of lactic acidosis. Metformin does not interact with specific foods; however, a consistent carbohydrate intake is recommended for glycemic control. The solution may be taken with food to reduce GI side effects. |
| Clinical Pearls | Riomet (metformin hydrochloride) oral solution 500 mg/5 mL is used for type 2 diabetes. Titrate slowly to minimize GI side effects; administer with meals. Monitor renal function (eGFR <30 contraindicated). Hold for procedures with iodinated contrast; restart after 48 hours if renal function stable. Avoid in hepatic impairment, acute MI, or sepsis. Lactic acidosis risk is rare but serious; monitor in patients with risk factors. May cause vitamin B12 deficiency with long-term use; check levels annually. |
| Patient Advice | Take with meals to reduce stomach upset. · Swallow the solution as directed; do not mix with other liquids unless specified. · Monitor blood glucose regularly as advised. · Report symptoms of lactic acidosis: unusual fatigue, muscle pain, trouble breathing, stomach pain, dizziness. · Avoid excessive alcohol intake (binge drinking) due to increased risk of lactic acidosis. · Inform all healthcare providers before any surgery or radiological procedure requiring contrast dye. · Do not stop taking without consulting your doctor; may need gradual dose adjustment. |