A 46-year-old man with type 2 diabetes mellitus is scheduled for cardiac catheterization in 2 days for undiagnosed, episodic chest pain. For 15 days, the patient has had retrosternal chest pain radiating to his arm, and it is becoming more frequent. He went to the emergency department 7 days ago due to chest pain. The patient was admitted for overnight observation but left against medical advice. Three sets of cardiac enzymes tests were negative, and his ECG showed nonspecific ST-T changes. He has a history of hypertension, a 6-year history of diabetes mellitus, and does not check his blood glucose levels regularly. Medications include metformin and lisinopril. At his last emergency department visit, laboratory results (chemistry profile and complete blood count) were normal, and he was started on low-dose aspirin. He has a long smoking history, and uses alcohol occasionally. The patient has a strong family history of premature coronary artery disease. Today, blood pressure is 127/70 mm Hg and pulse is 66/min. BMI is 30 kg/m². The remainder of the examination is within normal limits. Which of the following is the best next step in management of this patient?

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Quizplus · Accepted Answer

Explanation: Metformin's major side effects include gastrointestinal upset (eg, nausea, abdominal pain, diarrhea), decreased intestinal vitamin B12 absorption, and lactic acidosis. Lactic acidosis occurs rarely but can be fatal. Patients with normal renal and hepatic function can rarely develop lactic acidosis, but the incidence appears to be higher in those with abnormal renal function (eg, contraindicated for estimated glomerular filtration rate <30 mL/min/1.73 m²) or hepatic dysfunction. Other contraindications include active alcohol use, sepsis, and congestive heart failure (although many patients with well-compensated heart failure and normal renal function can tolerate metformin). Metformin given with large-dose intravenous iodine contrast (eg, cardiac catheterization) can increase the risk for lactic acidosis (given the potential for contrast-induced renal failure). As a result, most clinicians discontinue metformin on the day of intravenous iodine contrast exposure (regardless of baseline creatinine) and restart the drug at least 48 hours later after documenting stable renal function (Choice A). Because this patient's procedure is in 2 days, he can continue the metformin until then. (Choice B) Aspirin can cause platelet dysfunction for ≥1 week and so is usually discontinued at least 7 days before procedures with increased bleeding risk. However, aspirin can be continued safely during cardiac catheterization, and discontinuing aspirin can increase this patient's risk for myocardial infarction. (Choice C) ACE inhibitors (eg, lisinopril) have not been proven to cause increased risk for contrast-induced nephropathy. In fact, some studies have shown that ACE inhibitors may protect against contrast-induced nephropathy by blocking renal vasoconstriction. They are sometimes held on the day of the procedure only (ie, not 2 days before) to avoid potential prolonged hypotension. (Choice E) This patient is at goal blood pressure according to current guidelines and does not require additional antihypertensive therapy. Calcium channel blockers (eg, amlodipine) or thiazide diuretics can be added if this patient's blood pressure is not controlled. Educational objective: Metformin is contraindicated for patients with renal insufficiency, hepatic dysfunction, alcohol abuse, sepsis, or congestive heart failure (especially with estimated glomerular filtration rate <30 mL/min/1.73 m²). It can increase the risk for lactic acidosis when combined with large-dose intravenous iodine contrast (eg, during coronary angiography). Metformin is usually held on the day contrast is given and restarted at least 48 hours later after documenting stable renal function. References: Five things to know about...metformin and intravenous contrast. (http://www.ncbi.nlm.nih.gov/pubmed/23048079)

A 46-Year-Old Man with Type 2 Diabetes Mellitus Is Scheduled