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RIOMET®
(metformin hydrochloride) Oral Solution
WARNING
LACTIC ACIDOSIS
Postmarketing cases of metformin-associated lactic acidosis have resulted in death, hypothermia, hypotension, and resistant bradyarrhythmias. The onset of metforminassociated lactic acidosis is often subtle, accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, somnolence, and abdominal pain. Metforminassociated lactic acidosis was characterized by elevated blood lactate levels (>5 mmol/Liter), anion gap acidosis (without evidence of ketonuria or ketonemia), an increased lactate/pyruvate ratio; and metformin plasma levels generally >5 mcg/mL [see WARNINGS AND PRECAUTIONS].
Risk factors for metformin-associated lactic acidosis include renal impairment, concomitant use of certain drugs (e.g. carbonic anhydrase inhibitors such as topiramate), age 65 years old or greater, having a radiological study with contrast, surgery and other procedures, hypoxic states (e.g., acute congestive heart failure), excessive alcohol intake, and hepatic impairment.
Steps to reduce the risk of and managemetformin-associated lactic acidosis in these high risk groups are provided [see DOSAGE AND ADMINISTRATION, CONTRAINDICATIONS, WARNINGS AND PRECAUTIONS].
If metformin-associated lactic acidosis is suspected, immediately discontinue RIOMET and institute general supportive measures in a hospital setting. Prompt hemodialysis is recommended [see WARNINGS AND PRECAUTIONS].
RIOMET oral solution contains the biguanidine antihyperglycemic agent metformin in the form of monohydrochloride salt. Metformin hydrochloride, is N,N-dimethylimidodicarbonimidic diamide hydrochloride. The structural formula is shown as:
 |
Metformin hydrochloride, is a white crystalline powder with a molecular formula of C4H11N5•HCl and a molecular weight of 165.62. Metformin hydrochloride, USP 2.0 g is soluble in 20 mL of water. The pKa of metformin is 12.4. The pH of a 1% aqueous solution of metformin hydrochloride is 6.68. It is freely soluble in water; slightly soluble in alcohol; practically insoluble in acetone and in methylene chloride.
RIOMET (Cherry Flavor) contains 500 mg of metformin hydrochloride (the equivalent of 389.93 mg metformin) per 5 mL and the following inactive ingredients: Artificial cherry flavor, hydrochloric acid, potassium bicarbonate, purified water, saccharin calcium, and xylitol.
RIOMET (Strawberry Flavor) contains 500 mg of metformin hydrochloride (the equivalent of 389.93 mg metformin) per 5 mL and the following inactive ingredients: Hydrochloric acid, N&A strawberry flavor (propylene glycol and glycerin), potassium bicarbonate, purified water, sucralose, and xylitol.
RIOMET is indicated as an adjunct to diet and exercise to improve glycemic control in adults and pediatric patients 10 years of age and older with type 2 diabetes mellitus.
Discontinue RIOMET at the time of, or prior to, an iodinated contrast imaging procedure in patients with an eGFR between 30 and 60 mL/min/1.73 m²; in patients with a history of liver disease, alcoholism, or heart failure; or in patients who will be administered intra-arterial iodinated contrast. Re-evaluate eGFR 48 hours after the imaging procedure; restart RIOMET if renal function is stable.
Oral solution: 500 mg per 5 mL (100 mg/mL) clear solution in cherry and strawberry flavor
RIOMET 500 mg per 5 mL (100 mg/mL) oral solution is supplied in bottles with child-resistant caps and a dosing cup as follows:
| Flavor | Appearance | Size | NDC |
| Cherry | clear, colorless solution | 4 ounce (118 mL) | 10631-206-01 |
| 16 ounce (473 mL) | 10631-206-02 | ||
| Strawberry | clear, colorless to light yellow solution | 4 ounce (118 mL) | 10631-238-01 |
| 16 ounce (473 mL) | 10631-238-02 |
Store at 15° - 30° C (59° - 86° F) [See USP Controlled Room Temperature].
Manufactured by: Mikart, Inc., Atlanta, GA 30318. Distributed by: Sun Pharmaceutical Industries, Inc., Cranbury, NJ 08512. Revised: Nov 2018
The following adverse reactions are also discussed elsewhere in the labeling:
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
In a U.S. clinical trial of metformin HCl tablets in patients with type 2 diabetes mellitus, a total of 141 patients received metformin HCl tablets up to 2,550 mg per day. Adverse reactions reported in greater than 5% of patients treated with metformin HCl tablets and that were more common than in placebo-treated patients, are listed in Table 1.
Table 1: Adverse Reactions from a Clinical Trial of
Metformin HCl Tablets Occurring >5% and More Common than Placebo in Patients
with Type 2 Diabetes Mellitus
| Metformin HCl Tablets (n =141) |
Placebo (n = 145) |
|
| Diarrhea | 53% | 12% |
| Nausea/V omiting | 26% | 8% |
| Flatulence | 12% | 6% |
| Asthenia | 9% | 6% |
| Indigestion | 7% | 4% |
| Abdominal Discomfort | 6% | 5% |
| Headache | 6% | 5% |
Diarrhea led to discontinuation of metformin HCl tablets in 6% of patients. Additionally, the following adverse reactions were reported in ≥ 1% to ≤ 5% of patients treated with metformin HCl tablets and were more commonly reported than placebo: abnormal stools, hypoglycemia, myalgia, lightheaded, dyspnea, nail disorder, rash, sweating increased, taste disorder, chest discomfort, chills, flu syndrome, flushing, palpitation.
In clinical trials with metformin HCl tablets in pediatric patients with type 2 diabetes mellitus, the profile of adverse reactions was similar to that observed in adults.
In clinical trials of 29-week duration with metformin HCl tablets, a decrease to subnormal levels of previously normal serum vitamin B12 levels was observed in approximately 7% of patients.
The following adverse reactions have been identified during post approval use of metformin. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.
Cholestatic, hepatocellular, and mixed hepatocellular liver injury have been reported with postmarketing use of metformin.
Table 2 presents clinically significant drug interactions with RIOMET.
Table 2: Clinically Significant Drug Interactions with
RIOMET
| Carbonic Anhydrase Inhibitors | |
| Clinical Impact: | Carbonic anhydrase inhibitors frequently cause a decrease in serum bicarbonate and induce non-anion gap, hyperchloremic metabolic acidosis. Concomitant use of these drugs with RIOMET may increase the risk for lactic acidosis. |
| Intervention: | Consider more frequent monitoring of these patients. |
| Examples: | Topiramate, zonisamide, acetazolamide or dichlorphenamide. |
| Drugs that Reduce RIOMET Clearance | |
| Clinical Impact: | Concomitant use of drugs that interfere with common renal tubular transport systems involved in the renal elimination of metformin (e.g., organic cationic transporter-2 [OCT2\ / multidrug and toxin extrusion [MATE] inhibitors) could increase systemic exposure to metformin and may increase the risk for lactic acidosis [see CLINICAL PHARMACOLOGY]. |
| Intervention: | Consider the benefits and risks of concomitant use with RIOMET. |
| Examples: | Ranolazine, vandetanib, dolutegravir, and cimetidine. |
| Alcohol | |
| Clinical Impact: | Alcohol is known to potentiate the effect of metformin on lactate metabolism. |
| Intervention: | Warn patients against excessive alcohol intake while receiving RIOMET. |
| Insulin Secretagogues or Insulin | |
| Clinical Impact: | Coadministration of RIOMET with an insulin secretagogue (e.g., sulfonylurea) or insulin may increase the risk of hypoglycemia. |
| Intervention: | Patients receiving an insulin secretagogue or insulin may require lower doses of the insulin secretagogue or insulin. |
| Drugs Affecting Glycemic Control | |
| Clinical Impact: | Certain drugs tend to produce hyperglycemia and may lead to loss of glycemic control. |
| Intervention: | When such drugs are administered to a patient receiving RIOMET, observe the patient closely for loss of blood glucose control. When such drugs are withdrawn from a patient receiving RIOMET, observe the patient closely for hypoglycemia. |
| Examples: | Thiazides and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blockers, and isoniazid. |
Included as part of the PRECAUTIONS section.
There have been postmarketing cases of metformin-associated lactic acidosis, including fatal cases. These cases had a subtle onset and were accompanied by nonspecific symptoms such as malaise, myalgias, abdominal pain, respiratory distress, or increased somnolence; however, hypotension and resistant bradyarrhythmias have occurred with severe acidosis. Metforminassociated lactic acidosis was characterized by elevated blood lactate concentrations (> 5mmol/L), anion gap acidosis (without evidence of ketonuria or ketonemia), and an increased lactate: pyruvate ratio; metformin plasma levels were generally > 5 mcg/mL. Metformin decreases liver uptake of lactate increasing lactate blood levels which may increase the risk of lactic acidosis, especially in patients at risk.
If metformin-associated lactic acidosis is suspected, general supportive measures should be instituted promptly in a hospital setting, along with immediate discontinuation of RIOMET. In RIOMET treated patients with a diagnosis or strong suspicion of lactic acidosis, prompt hemodialysis is recommended to correct the acidosis and remove accumulated metformin (metformin hydrochloride is dialyzable with a clearance of up to 170 mL/min under good hemodynamic conditions). Hemodialysis has often resulted in reversal of symptoms and recovery.
Educate patients and their families about the symptoms of lactic acidosis and, if these symptoms occur, instruct them to discontinue RIOMET and report these symptoms to their healthcare provider.
For each of the known and possible risk factors for metformin-associated lactic acidosis, recommendations to reduce the risk of and manage metformin-associated lactic acidosis are provided below:
The postmarketing metformin-associated lactic acidosis cases primarily occurred in patients with significant renal impairment.
The risk of metformin accumulation and metformin-associated lactic acidosis increases with the severity of renal impairment because metformin is substantially excreted by the kidney. Clinical recommendations based upon the patient's renal function include [see DOSAGE AND ADMINISTRATION, CLINICAL PHARMACOLOGY]:
The concomitant use of RIOMET with specific drugs may increase the risk of metformin-associated lactic acidosis: those that impair renal function, result in significant hemodynamic change, interfere with acid-base balance, or increase metformin accumulation. Consider more frequent monitoring of patients [see DRUG INTERACTIONS].
The risk of metformin-associated lactic acidosis increases with the patient's age because elderly patients have a greater likelihood of having hepatic, renal, or cardiac impairment than younger patients. Assess renal function more frequently in elderly patients.
Administration of intravascular iodinated contrast agents in metformin-treated patients has led to an acute decrease in renal function and the occurrence of lactic acidosis. Stop RIOMET at the time of, or prior to, an iodinated contrast imaging procedure in patients with an eGFR between 30 and 60 mL/min/1.73 m²; in patients with a history of hepatic impairment, alcoholism or heart failure; or in patients who will be administered intraarterial iodinated contrast. Re-evaluate eGFR 48 hours after the imaging procedure, and restart RIOMET if renal function is stable.
Withholding of food and fluids during surgical or other procedures may increase the risk for volume depletion, hypotension, and renal impairment. RIOMET should be temporarily discontinued while patients have restricted food and fluid intake.
Several of the postmarketing cases of metformin-associated lactic acidosis occurred in the setting of acute congestive heart failure (particularly when accompanied by hypoperfusion and hypoxemia). Cardiovascular collapse (shock), acute myocardial infarction, sepsis, and other conditions associated with hypoxemia have been associated with lactic acidosis and may cause prerenal azotemia. When such an event occurs, discontinue RIOMET.
Alcohol potentiates the effect of metformin on lactate metabolism. Patients should be warned against excessive alcohol intake while receiving RIOMET.
Patients with hepatic impairment have developed cases of metforminassociated lactic acidosis. Thismay be due to impaired lactate clearance resulting in higher lactate blood levels. Therefore, avoid use of RIOMET in patients with clinical or laboratory evidence of hepatic disease.
In clinical trials of 29-week duration with metformin hydrochloride (HCl) tablets, a decrease to subnormal levels of previously normal serum vitamin B12 levels was observed in approximately 7% of patients. Such decrease, possibly due to interference with B12 absorption from the B12-intrinsic factor complex, may be associated with anemia but appears to be rapidly reversible with discontinuation of metformin or vitamin B12 supplementation. Certain individuals (those with inadequate vitamin B12 or calcium intake or absorption) appear to be predisposed to developing subnormal vitamin B12 levels. Measure hematologic parameters on an annual basis and vitamin B12 at 2 to 3 year intervals in patients on RIOMET and manage any abnormalities [see ADVERSE REACTIONS].
Insulin and insulin secretagogues (e.g., sulfonylurea) are known to cause hypoglycemia. RIOMET may increase the risk of hypoglycemia when combinedwith insulin and/or an insulin secretagogue. Therefore, a lower dose of insulin or insulin secretagogue may be required to minimize the risk of hypoglycemia when used in combination with RIOMET [see DRUG INTERACTIONS].
There have been no clinical studies establishing conclusive evidence of macrovascular risk reduction with RIOMET.
Advise the patient to read the FDA-approved patient labeling (PATIENT INFORMATION).
Instruct patients or caregivers to use the supplied dosing cup to measure the prescribed amount of medication. Inform patients that additional RIOMET dosing cups or oral dosing syringes may be obtained from their pharmacy.
Explain the risks of lactic acidosis, its symptoms, and conditions that predispose to its development. Advise patients to discontinue RIOMET immediately and to promptly notify their healthcare provider if unexplained hyperventilation, myalgias, malaise, unusual somnolence or other nonspecific symptoms occur. Counsel patients against excessive alcohol intake and inform patients about importance of regular testing of renal function while receiving RIOMET. Instruct patients to informtheir doctor that they are taking RIOMET prior to any surgical or radiological procedure, as temporary discontinuation may be required [see WARNINGS AND PRECAUTIONS].
Inform patients that hypoglycemia may occur when RIOMET is coadministered with oral sulfonylureas and insulin. Explain to patients receiving concomitant therapy the risks of hypoglycemia, its symptoms and treatment, and conditions that predispose to its development [see WARNINGS AND PRECAUTIONS].
Inform patients about importance of regular hematological parameters while receiving RIOMET [see WARNINGS AND PRECAUTIONS].
Inform females that treatment with RIOMET may result in ovulation in some premenopausal anovulatory women which may lead to unintended pregnancy [see Use In Specific Populations].
Long-term carcinogenicity studies have been performed in rats (dosing duration of 104 weeks) and mice (dosing duration of 91 weeks) at doses up to and including 900 mg/kg/day and 1,500 mg/kg/day, respectively. These doses are both approximately 3 times the maximum recommended human daily dose of 2,550 mg based on body surface area comparisons. No evidence of carcinogenicity with metformin was found in either male or female mice. Similarly, there was no tumorigenic potential observed with metformin in male rats. There was, however, an increased incidence of benign stromal uterine polyps in female rats treated with 900 mg/kg/day.
There was no evidence of a mutagenic potential of metformin in the following in vitro tests: Ames test (S. typhimurium), gene mutation test (mouse lymphoma cells), or chromosomal aberrations test (human lymphocytes). Results in the in vivo mouse micronucleus test were also negative.
Fertility of male or female rats was unaffected by metformin when administered at doses as high as 600 mg/kg/day, which is approximately 2 times the maximum recommended human daily dose of 2,550 mg based on body surface area comparisons.
Limited data with RIOMET in pregnant women are not sufficient to determine a drug-associated risk for major birth defects or miscarriage. Published studies with metformin use during pregnancy have not reported a clear association with metformin and major birth defect or miscarriage risk [see Data]. There are risks to the mother and fetus associated with poorly controlled diabetes mellitus in pregnancy [see Clinical Considerations].
No adverse developmental effects were observed when metformin was administered to pregnant Sprague Dawley rats and rabbits during the period of organogenesis at doses up to 2- and 5times, respectively, a 2,550 mg clinical dose, based on body surface area [see Data].
The estimated background risk of major birth defects is 6 to 10% in women with pre-gestational diabetes mellitus with an HbA1C >7 and has been reported to be as high as 20 to 25% in women with a HbA1C >10. The estimated background risk of miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.
Disease-Associated Maternal And/Or Embryo/Fetal Risk
Poorly-controlled diabetes mellitus in pregnancy increases the maternal risk for diabetic ketoacidosis, pre-eclampsia, spontaneous abortions, preterm delivery, stillbirth and delivery complications. Poorly controlled diabetes mellitus increases the fetal risk for major birth defects, stillbirth, and macrosomia related morbidity.
Human Data
Published data from post-marketing studies have not reported a clear association with metformin and major birth defects, miscarriage, or adverse maternal or fetal outcomes when metformin was used during pregnancy. However, these studies cannot definitely establish the absence of any metforminassociated risk because of methodological limitations, including small sample size and inconsistent comparator groups.
Animal Data
Metformin hydrochloride did not adversely affect development outcomes when administered to pregnant rats and rabbits at doses up to 600 mg/kg/day. This represents an exposure of about 2 and 5 times a 2,550 mg clinical dose based on body surface area comparisons for rats and rabbits, respectively. Determination of fetal concentrations demonstrated a partial placental barrier to metformin.
Limited published studies report thatmetformin is present in human milk [see Data]. However, there is insufficient information to determine the effects of metformin on the breastfed infant and no available information on the effects of metformin on milk production. Therefore, the developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for RIOMET and any potential adverse effects on the breastfed child from RIOMET or from the underlying maternal condition.
Published clinical lactation studies report that metformin is present in human milk which resulted in infant doses approximately 0.11% to 1% of the maternal weight-adjusted dosage and a milk/plasma ratio ranging between 0.13 and 1. However, the studies were not designed to definitely establish the risk of use of metformin during lactation because of small sample size and limited adverse event data collected in infants.
Discuss the potential for unintended pregnancy with premenopausal women as therapy with RIOMET may result in ovulation in some anovulatory women.
The safety and effectiveness of RIOMET for the treatment of type 2 diabetes mellitus have been established in pediatric patients 10 to 16 years old. Safety and effectiveness of RIOMET have not been established in pediatric patients less than 10 years old.
Use of RIOMET in pediatric patients 10 to 16 years old for the treatment of type 2 diabetes mellitus is supported by evidence from adequate and well-controlled studies of metformin HCl tablets in adults with additional data from a controlled clinical study of metformin HCl tablets in pediatric patients 10 to 16 years old with type 2 diabetes mellitus, which demonstrated a similar response in glycemic control to that seen in adults [see Clinical Studies]. In this study, adverse reactions were similar to those described in adults. A maximum daily dose of 2,000 mg of RIOMET is recommended. [See DOSAGE AND ADMINISTRATION]
Controlled clinical studies of metformin HCl tablets did not include sufficient numbers of elderly patients to determine whether they respond differently from younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy and the higher risk of lactic acidosis. Assess renal function more frequently in elderly patients [see WARNINGS AND PRECAUTIONS].
Metformin is substantially excreted by the kidney, and the risk of metformin accumulation and lactic acidosis increases with the degree of renal impairment. RIOMET is contraindicated in severe renal impairment, patients with an estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m² [see DOSAGE AND ADMINISTRATION, CONTRAINDICATIONS, WARNINGS AND PRECAUTIONS, and CLINICAL PHARMACOLOGY].
Use of metformin in patients with hepatic impairment has been associated with some cases of lactic acidosis. RIOMET is not recommended in patients with hepatic impairment. [see WARNINGS AND PRECAUTIONS].
Overdose of metformin hydrochloride has occurred, including ingestion of amounts greater than 50 grams. Hypoglycemia was reported in approximately 10% of cases, but no causal association with metformin has been established. Lactic acidosis has been reported in approximately 32% of metformin overdose cases [see WARNINGS AND PRECAUTIONS]. Metformin is dialyzable with a clearance of up to 170mL/min under good hemodynamic conditions. Therefore, hemodialysismay be useful for removal of accumulated drug from patients in whom metformin overdosage is suspected.
RIOMET is contraindicated in patients with:
Metformin is an antihyperglycemic agent which improves glucose tolerance in patients with type 2 diabetes mellitus, lowering both basal and postprandial plasma glucose.Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose, and improves insulin sensitivity by increasing peripheral glucose uptake and utilization. With metformin therapy, insulin secretion remains unchanged while fasting insulin levels and day-long plasma insulin response may decrease.
Two pharmacokinetic studies performed in healthy volunteers to evaluate the bioavailability of RIOMET in comparison with metformin HCl tablets under fasting and fed conditions showed that the rate and extent of absorption of RIOMET was found to be comparable to that of metformin HCl tablets under fasting or fed conditions (see Table 3).
Table 3: Select Mean (± S.D.) Pharmacokinetic
Parameters Following Single Oral Doses of 1000 mg RIOMET and Metformin HCl
tablets in healthy, nondiabetic adults (n = 36) under fed and fasting
conditions
| Formulation | Cmax (ng/mL) | AUC0-∞ (ng•h/mL) | Tmax (h) |
| Study 1- Fasting state | |||
| RIOMET | 1540.1 ± 451.1 | 9069.6 ± 2593.6 | 2.2 ± 0.5 |
| Metformin HCl Tablets | 1885.1 ± 498.5 | 11100.1± 2733.1 | 2.5 ± 0.6 |
| T/R Ratio X 100 (90% confidence interval) | 81.2 (76.3 to 86.4) | 81.2 (76.9 to 85.6) | - |
| Study 2- Fed State | |||
| RIOMET | 1235.3 ± 177.7 | 8950.1 ± 1381.2 | 4.1 ± 0.8 |
| Metformin HCl Tablets | 1361 ± 298.8 | 9307.7 ± 1839.8 | 3.7 ± 0.8 |
| T/R Ratio X 100 (90% confidence interval) | 91.8 (87.4 to 96.5) | 97.0 (92.9 to 101.2) | - |
| T-test product (RIOMET) R-reference product (immediate release metformin HCl tablets) |
|||
Studies using single oral doses of metformin HCl tablets 500 mg to 1,500 mg, and 850 mg to 2,550 mg, indicate that there is a lack of dose proportionality with increasing doses, which is due to decreased absorption rather than an alteration in elimination. At usual clinical doses and dosing schedules of metformin, steady state plasma concentrations of metformin are reached within 24 to 48 hours and are generally < 1 mcg/mL.
Effect Of Food
The food-effect study assessed the effects of a high fat/high calorie meal and a low fat/low calorie meal on the bioavailability of RIOMET in comparison with administration in the fasted state, in healthy volunteers. The extent of absorption was increased by approximately 16% and 13% with the low fat/low calorie meal and the high fat/high calorie meal, respectively, compared with the administration in the fasted state. The rate and extent of absorption with high fat/high calorie and low fat/ low calorie meal were similar. The mean tmax was 2.5 hours under fasting conditions as compared to 3.9 hours with both low fat/ low calorie meal and high fat/high calorie meals (see Table 4).
Table 4: Select Mean (± S.D.) Metformin
Pharmacokinetic Parameters Following Single Oral Doses of 1,000 mg RIOMET in
healthy, nondiabetic adults (n = 33) under fed (high fat/high calorie meal and
low fat/low calorie meal) and fasting conditions (study 3)
| Meal type | Cmax (ng/mL) | AUC0-∞ (ng•h/mL) | tmax (h) |
| Fasting (F) | 1641.5 ± 551.8 | 9982.9 ± 2544.5 | 2.5 ± 0.9 |
| Low fat/ low calorie meal (L) | 1525.8 ± 396.7 | 11542.0 ± 2947.5 | 3.9 ± 0.6 |
| High fat/high calorie meal (H) | 1432.5 ± 346.8 | 11184.5 ± 2446.1 | 3.9 ± 0.8 |
| L/F Ratio X 100 (90% confidence interval) | 94.6 (84.0 to 106.5) | 115.6 (103.6 to 128.9) | - |
| H/F Ratio X 100 (90% confidence interval) | 89.4 (79.4 to 100.6) | 112.6 (100.9 to 125.6) | - |
| L/H Ratio X 100 (90% confidence interval) | 105.8 (94.0 to 119.2) | 102.7 (92.0 to 114.6) | - |
The apparent volume of distribution (V/F) of metformin following single oral doses of metformin HCl 850 mg averaged 654 ± 358 L. Metformin is negligibly bound to plasma proteins. Metformin partitions into erythrocytes, most likely as a function of time.
Intravenous single-dose studies in normal subjects demonstrate that metformin is excreted unchanged in the urine and does not undergo hepatic metabolism (no metabolites have been identified in humans) nor biliary excretion.
Renal clearance (see Table 5) is approximately 3.5 times greater than creatinine clearance, which indicates that tubular secretion is the major route of metformin elimination. Following oral administration, approximately 90% of the absorbed drug is eliminated via the renal route within the first 24 hours, with a plasma elimination half-life of approximately 6.2 hours. In blood, the elimination half-life is approximately 17.6 hours, suggesting that the erythrocyte mass may be a compartment of distribution.
In patients with decreased renal function the plasma and blood half-life of metformin is prolonged and the renal clearance is decreased (see Table 5) [See DOSAGE AND ADMINISTRATION, CONTRAINDICATIONS, WARNINGS AND PRECAUTIONS and Use In Specific Populations].
No pharmacokinetic studies of metformin have been conducted in patients with hepatic impairment [See WARNINGS AND PRECAUTIONS and Use In Specific Populations].
Limited data from controlled pharmacokinetic studies of metformin HCl tablets in healthy elderly subjects suggest that total plasma clearance of metformin is decreased, the half-life is prolonged, and Cmax is increased, compared to healthy young subjects. It appears that the change in metformin pharmacokinetics with aging is primarily accounted for by a change in renal function (see Table 5). [See WARNINGS AND PRECAUTIONS and Use In Specific Populations].
Table 5: Select Mean (±S.D.) Metformin Pharmacokinetic
Parameters Following Single or Multiple Oral Doses of Metformin HCl Tablets
| Subject Groups: Metformin HCl dosea (number of subjects) | Cmaxb (mcg/mL) | Tmax c(hrs) | Renal Clearance (mL/min) |
| Healthy, nondiabetic adults: | |||
| 500 mg single dose (24) | 1.03 (± 0.33) | 2.75 (±0.81) | 600 (±132) |
| 850 mg single dose (74)d | 1.60 (±0.38) | 2.64 (±0.82) | 552 (±139) |
| 850 mg three times daily for 19 doses (9)e | 2.01 (±0.42) | 1.79 (±0.94) | 642 (±173) |
| Adults with type 2 diabetes mellitus: | |||
| 850 mg single dose (23) | 1.48 (±0.5) | 3.32 (±1.08) | 491 (±138) |
| 850 mg three times daily for 19 dosese (9) | 1.90 (±0.62) | 2.01 (±1.22) | 550 (±160) |
| Elderly,f healthy nondiabetic adults: | |||
| 850 mg single dose (12) | 2.45 (±0.70) | 2.71 (±1.05) | 412 (±98) |
| Renal-impaired adults: | |||
| 850 mg single dose | |||
| Mild (CLcr g 61 to 90 mL/min) (5) | 1.86 (±0.52) | 3.20 (±0.45) | 384 (±122) |
| Moderate (CLcr 31 to 60 mL/min) (4) | 4.12 (±1.83) | 3.75 (±0.50) | 108 (±57) |
| Severe (CLcr 10 to 30 mL/min) (6) | 3.93 (±0.92) | 4.01 (±1.10) | 130 (±90) |
| a All doses given fasting except the first 18
doses of the multiple dose studies b Peak plasma concentration c Time to peak plasma concentration d Combined results (average means) of five studies: mean age 32 years (range 23 to 59 years) e Kinetic study done following dose 19, given fasting f Elderly subjects, mean age 71 years (range 65 to 81 years) g CLcr = creatinine clearance normalized to body surface area of 1.73 m² |
|||
After administration of a single oral metformin HCl 500 mg tablet with food, geometric mean metformin Cmax and AUC differed less than 5% between pediatric type 2 diabetic patients (12 to 16 years of age) and gender- and weight-matched healthy adults (20 to 45 years of age), all with normal renal function.
Metformin pharmacokinetic parameters did not differ significantly between normal subjects and patients with type 2 diabetes mellitus when analyzed according to gender (males = 19, females = 16).
No studies of metformin pharmacokinetic parameters according to race have been performed.
Table 6: Effect of Coadministered Drug on Plasma
Metformin Systemic Exposure
| Coadministered Drug | Dose of Coadministered Drug* | Dose of Metformin HCl* | Geometric Mean Ratio (ratio with/without coadministered drug) No Effect = 1.00 | ||
| AUC† | Cmax | ||||
| No dosing adjustments required for the following: | |||||
| Glyburide | 5 mg | 850 mg | metformin | 0.91‡ | 0.93‡ |
| Furosemide | 40 mg | 850 mg | metformin | 1.09‡ | 1.22‡ |
| Nifedipine | 10 mg | 850 mg | metformin | 1.16 | 1.21 |
| Propranolol | 40 mg | 850 mg | metformin | 0.90 | 0.94 |
| Ibuprofen | 400 mg | 850 mg | metformin | 1.05‡ | 1.07‡ |
| Cationic drugs eliminated by renal tubular secretion may reduce metformin elimination [See WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS.] | |||||
| Cimetidine | 400 mg | 850 mg | metformin | 1.40 | 1.61 |
| Carbonic anhydrase inhibitors may cause metabolic acidosis [See WARNINGS AND PRECAUTIONS and DRUG INTERACTIONS.] | |||||
| Topiramate | 100 mg § | 500 mg § | metformin | 1.25 § | 1.17 |
| * All metformin HCl and coadministered drugs were given
as single doses † AUC = AUC (INF) ‡Ratio of arithmetic means § At steady state with topiramate 100 mg every 12 hours and metformin 500 mg every 12 hours; AUC = AUC0-12h |
|||||
Table 7: Effect of Metformin on Coadministered Drug
Systemic Exposure
| Coadministered Drug | Dose of Coadministered Drug* | Dose of Metformin HCl* | Geometric Mean Ratio (ratio with/without metformin) No Effect = 1.00 | ||
| AUC† | Cmax | ||||
| No dosing adjustments required for the following: | |||||
| Glyburide | 5 mg | 850 mg | glyburide | 0.78‡ | 0.63‡ |
| Furosemide | 40 mg | 850 mg | furosemide | 0.87 ‡ | 0.69 ‡ |
| Nifedipine | 10 mg | 850 mg | nifedipine | 1.10§ | 1.08 |
| Propranolol | 40 mg | 850 mg | propranolol | 1.01§ | 1.02 |
| Ibuprofen | 400 mg | 850 mg | ibuprofen | 0.97 ¶ | 1.01 ¶ |
| Cimetidine | 400 mg | 850 mg | cimetidine | 0.95 § | 1.01 |
| * All metformin HCl and coadministered drugs were given
as single doses † AUC = AUCinf unless otherwise noted ‡ Ratio of arithmetic means, p-value of difference < 0.05 § AUC0-24 hr reported ¶ Ratio of arithmetic means |
|||||
A double-blind, placebo-controlled,multicenter US clinical trial involving obese patients with type 2 diabetes mellitus whose hyperglycemia was not adequately controlled with dietary management alone (baseline fasting plasma glucose [FPG] of approximately 240 mg/dL) was conducted. Patients were treated with metformin HCl tablets (up to 2,550 mg/day) or placebo for 29 weeks. The results are presented in Table 8.
Table 8: Mean Change in Fasting Plasma Glucose and
HbA1c at Week 29 Comparing Metformin HCl Tablets vs Placebo in Patients with
Type 2 Diabetes Mellitus
| Metformin HCL Tablets (n=141) |
Placebo (n=145) |
p-Value | |
| FPG (mg/dL) | |||
| Baseline | 241.5 | 237.7 | NS* |
| Change at FINAL VISIT | -53.0 | 6.3 | 0.001 |
| Hemoglobin A1c (%) | |||
| Baseline | 8.4 | 8.2 | NS* |
| Change at FINAL VISIT | -1.4 | 0.4 | 0.001 |
| * Not statistically significant | |||
Mean baseline body weight was 201 lbs and 206 lbs in the metformin HCl tablet and placebo arms, respectively. Mean change in body weight from baseline to week 29 was -1.4 lbs and -2.4 lbs in the metformin HCl tablet and placebo arms, respectively.
A 29-week, double-blind, placebo-controlled study of metformin HCl tablet and glyburide, alone and in combination, was conducted in obese patients with type 2 diabetes mellitus who had failed to achieve adequate glycemic control while on maximum doses of glyburide (baseline FPG of approximately 250 mg/dL). Patients randomized to the combination arm started therapy with metformin HCl tablet 500 mg and glyburide 20 mg. At the end of each week of the first 4 weeks of the trial, these patients had their dosages of metformin HCl increased by 500 mg if they had failed to reach target fasting plasma glucose. After week 4, such dosage adjustments were made monthly, although no patient was allowed to exceed metformin HCl 2,500 mg. Patients in the metformin only arm (metformin HCl plus placebo) discontinued glyburide and followed the same titration schedule. Patients in the glyburide arm continued the same dose of glyburide. At the end of the trial, approximately 70% of the patients in the combination group were taking metformin HCl 2,000 mg/glyburide 20 mg or metformin HCl 2,500 mg/glyburide 20 mg. The results are displayed in Table 9.
Table 9: Mean Change in Fasting Plasma Glucose and
HbA1c at Week 29 Comparing Metformin HCl Tablets/Glyburide (Comb) vs Glyburide
(Glyb) vs Metformin HCl Tablets (GLU): in Patients with Type 2 Diabetes Mellitus
with Inadequate Glycemic Control on Glyburide
| Comb (n = 213) |
Glyb (n = 209) |
GLU (n = 210) |
p-Values | |||
| Glyb vs Comb | GLU vs Comb | GLU vs Glyb | ||||
| Fasting Plasma Glucose (mg/dL) | ||||||
| Baseline | 250.5 | 247.5 | 253.9 | NS* | NS* | NS* |
| Change at FINAL VISIT | -63.5 | 13.7 | -0.9 | 0.001 | 0.001 | 0.025 |
| Hemoglobin A1c (%) | ||||||
| Baseline | 8.8 | 8.5 | 8.9 | NS* | NS* | 0.007 |
| Change at FINAL VISIT | -1.7 | 0.2 | -0.4 | 0.001 | 0.001 | 0.001 |
| * Not statistically significant | ||||||
Mean baseline body weight was 202 lbs, 203 lbs, and 204 lbs in the metformin HCl tablet/glyburide, glyburide, and metformin HCl tablet arms, respectively. Mean change in body weight from baseline to week 29 was 0.9 lbs, -0.7 lbs, and -8.4 lbs in the metformin HCl tablet/glyburide, glyburide, and metformin HCl tablet arms, respectively.
A double-blind, placebo-controlled study was conducted in pediatric patients aged 10 to 16 years with type 2 diabetes mellitus (mean FPG 182.2 mg/dL), where patients were treated with metformin HCl tablets (up to 2,000 mg/day) for up to 16 weeks (mean duration of treatment 11 weeks). The results are displayed in Table 10.
Table 10: Mean Change in Fasting Plasma Glucose at
Week 16 Comparing Metformin HCl Tablets vs Placebo in Pediatric Patientsa with
Type 2 Diabetes Mellitus
| Metformin HCl Tablets | Placebo | p-Value | |
| FPG (mg/dL) | (n = 37) | (n = 36) | |
| Baseline | 162.4 | 192.3 | |
| Change at FINAL VISIT | -42.9 | 21.4 | <0.001 |
| a Pediatric patients mean age 13.8 years (range 10 to16 years) | |||
Mean baseline body weight was 205 lbs and 189 lbs in the metformin HCl tablet and placebo arms, respectively. Mean change in body weight from baseline to week 16 was -3.3 lbs and -2.0 lbs in the metformin HCl tablet and placebo arms, respectively.
RIOMET
(ree oh met)
(metformin hydrochloride) oral solution
What is the most important information I should know about RIOMET?
RIOMET can cause serious side effects, including:
Lactic Acidosis. Metformin hydrochloride, the medicine in RIOMET, can cause a rare, but serious side effect called lactic acidosis (a build-up of lactic acid in the blood) that can cause death. Lactic acidosis is a medical emergency and must be treated in a hospital.
Stop taking RIOMET and call your healthcare provider right away if you get any of the following symptoms of lactic acidosis:
You have a higher chance of getting lactic acidosis if you:
Tell your healthcare provider if you have any of the problems in the list above.
Tell your healthcare provider that you are taking RIOMET before you have surgery or x-ray tests. Your healthcare provider may need to stop RIOMET for a while if you have surgery or certain x-ray tests.
RIOMET can have other serious side effects. See “What are the possible side effects of RIOMET?”
What is RIOMET?
Do not take RIOMET if you:
Before taking RIOMET tell your healthcare provider about all your medical conditions, including if you:
Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Know the medicines you take. Keep a list of them to show your healthcare provider and pharmacist when you get a new medicine.
RIOMET may affect the way other medicines work, and other medicines may affect how RIOMET works.
How should I take RIOMET?
What should I avoid while taking RIOMET?
Do not drink a lot of alcoholic drinks while taking RIOMET. This means you should not binge drink for short periods, and you should not drink a lot of alcohol on a regular basis. Alcohol can increase the chance of getting lactic acidosis.
What are the possible side effects of RIOMET?
RIOMET may cause serious side effects, including:
Common side effects of RIOMET include:
These are not all the possible side effects of RIOMET.
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
How should I store RIOMET?
General information about the safe and effective use of RIOMET.
Medicines are sometimes prescribed for purposes other than those listed in a Patient Information leaflet. Do not use RIOMET for a condition for which it was not prescribed. Do not give RIOMET to other people, even if they have the same symptoms that you have. It may harm them.
You can ask your pharmacist or healthcare provider for information about RIOMET that is written for health professionals.
What are the ingredients of RIOMET?
Active ingredients: metformin hydrochloride.
Inactive ingredients (Cherry Flavor): Artificial cherry flavor, hydrochloric acid, potassium bicarbonate, purified water, saccharin calcium, and xylitol.
Inactive ingredients (Strawberry Flavor): Hydrochloric acid, N&A strawberry flavor (propylene glycol and glycerin), potassium bicarbonate, purified water, sucralose, and xylitol.
This Patient Information has approved by the U.S. Food and Drug Administration
