Lactic Acidosis: Postmarketing cases of metformin-associated lactic acidosis, including fatal cases, were reported. These cases had a subtle onset and were accompanied by nonspecific symptoms such as malaise, myalgias, abdominal pain, respiratory distress, or increased somnolence; however, hypothermia, hypotension, and resistant bradyarrhythmias have occurred with severe acidosis. Additional findings included elevated blood lactate concentrations (>5 mmol/L), anion gap acidosis (without evidence of ketonuria or ketonemia), an increased lactate:pyruvate ratio, and metformin plasma levels generally >5 mcg/mL.
If metformin-associated lactic acidosis is suspected, general supportive measures should be instituted promptly in a hospital setting, along with immediate discontinuation of INVOKAMET®/INVOKAMET® XR. Prompt hemodialysis is recommended to correct the acidosis and remove accumulated metformin.
Educate patients and their families about the symptoms of lactic acidosis and if symptoms occur instruct them to discontinue INVOKAMET®/INVOKAMET® XR and report these symptoms to their healthcare provider.
Recommendations to reduce the risk include:
Renal Impairment: Obtain an eGFR before initiation and at least annually thereafter, and more frequently in patients at increased risk of renal impairment.
Drug Interactions: More frequent monitoring is recommended when administered with drugs that impair renal function, result in hemodynamic change, interfere with acid-base balance, or increase metformin accumulation (eg, cationic drugs).
Age 65 or Greater: Assess renal function more frequently in elderly patients.
Radiological Studies with Contrast: Stop INVOKAMET®/INVOKAMET® XR at the time of, or prior to, an iodinated contrast imaging procedure in patients with an eGFR of 45 to 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 intra-arterial iodinated contrast. Re-evaluate eGFR 48 hours after the imaging procedure, and restart INVOKAMET®/INVOKAMET® XR if renal function is stable.
Surgery and Other Procedures: Discontinue INVOKAMET®/INVOKAMET® XR while patients have restricted food and fluid intake.
Hypoxic States: Discontinue INVOKAMET®/INVOKAMET® XR in conditions associated with hypoxemia.
Excessive Alcohol Intake: Warn patients against excessive alcohol intake while receiving INVOKAMET®/INVOKAMET® XR.
Hepatic Impairment: Avoid use of INVOKAMET®/INVOKAMET® XR in patients with evidence of hepatic disease.
Lower-Limb Amputation: An approximately 2-fold increased risk of lower-limb amputations associated with INVOKANA® was observed in CANVAS and CANVAS-R, two randomized, placebo-controlled trials evaluating patients with type 2 diabetes who had either established cardiovascular disease or were at risk for cardiovascular disease. The risk of lower-limb amputations was observed at both the 100-mg and 300-mg once-daily dosage regimens.
Amputations of the toe and midfoot (99 out of 140 patients with amputations receiving INVOKANA® in the two trials) were the most frequent; however, amputations involving the leg, below and above the knee, were also observed (41 out of 140 patients with amputations receiving INVOKANA® in the two trials). Some patients had multiple amputations, some involving both lower limbs.
Lower-limb infections, gangrene, and diabetic foot ulcers were the most common precipitating medical events leading to the need for an amputation. The risk of amputation was highest in patients with a baseline history of prior amputation, peripheral vascular disease, and neuropathy.
Before initiating, consider factors in the patient history that may predispose to the need for amputations, such as a history of prior amputation, peripheral vascular disease, neuropathy, and diabetic foot ulcers. Counsel patients about the importance of routine preventative foot care. Monitor patients for signs and symptoms of infection (including osteomyelitis), new pain or tenderness, sores, or ulcers involving the lower limbs, and discontinue if these complications occur.