A 68-year-old man presents to the clinic for a routine diabetes follow-up. He has a 12-yea… — USMLE Step 3

A $68$ -year-old man presents to the clinic for a routine diabetes follow-up. He has a $12$ -year history of type 2 diabetes mellitus, hypertension, and hyperlipidemia. His current medications include metformin $1000\text{ mg}$ twice daily, amlodipine $5\text{ mg}$ daily, atorvastatin $40\text{ mg}$ daily, and aspirin $81\text{ mg}$ daily. He feels well and reports no polyuria, polydipsia, or peripheral edema.

Vital signs are temperature $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure $132/80\text{ mmHg}$ , and heart rate $72/\text{min}$ . Physical examination reveals diminished vibratory sensation in both feet but is otherwise unremarkable.

Laboratory results are as follows:

Test	Result
Hemoglobin A1c	$7.1\%$
Serum sodium	$139\text{ mEq/L}$
Serum potassium	$4.4\text{ mEq/L}$
Serum creatinine	$1.7\text{ mg/dL}$ (baseline $1.2\text{ mg/dL}$ two years ago)
Estimated GFR	$42\text{ mL/min/1.73 m}^2$

Urinalysis shows microalbuminuria but no hematuria or cellular casts.

Based on the laboratory findings, which of the following is the most appropriate next step in the management of this patient's pharmacotherapy?

Reduce the metformin dosage to $500\text{ mg}$ twice daily and recheck renal function in $3$ months.Answer
B
Continue the current medication regimen and schedule a follow-up basic metabolic panel in $1$ year.
C
Discontinue metformin completely and initiate daily basal insulin injections.
D
Maintain the current regimen and obtain a renal duplex ultrasound.
E
Refer the patient for a percutaneous renal biopsy to evaluate the etiology of renal decline.

Answer

Reduce the metformin dosage to

500\text{ mg}

twice daily and recheck renal function in

3

months.

The correct action is to reduce the metformin dosage by half and monitor renal function closely. Metformin is excreted unchanged in the urine, and impaired renal function causes the drug to accumulate, which inhibits hepatic gluconeogenesis and mitochondrial respiration, increasing the risk of lactic acidosis. According to current guidelines, metformin does not need to be discontinued unless the eGFR falls below

30\text{ mL/min/1.73 m}^2

. However, when the eGFR is between

30

and

45\text{ mL/min/1.73 m}^2

(as in this patient with an eGFR of

42

), the maximum recommended daily dose is

1000\text{ mg}

, and renal function should be monitored every

3

6

months.

Step-by-Step Solution

Evaluate the patient's current renal function against historical baseline.

The eGFR has declined from a normal baseline to

42\text{ mL/min/1.73 m}^2

, indicating the progression to stage 3b chronic kidney disease (CKD).

Recognizing the current stage of CKD is necessary to evaluate the safety and dosing of renally cleared medications.

Review the patient's medication list for drugs requiring dose adjustment based on the new eGFR.

The patient is taking metformin

1000\text{ mg}

twice daily (total

2000\text{ mg/day}

Metformin can accumulate in renal impairment, leading to a rare but life-threatening complication known as metformin-associated lactic acidosis.

Apply evidence-based guidelines for metformin use in CKD.

Guidelines recommend that if eGFR falls to

30-45\text{ mL/min/1.73 m}^2

, the dose should be reduced by

50\%

(maximum

1000\text{ mg/day}

) and renal function monitored every

3

6

months. It is only absolutely contraindicated if eGFR is

< 30\text{ mL/min/1.73 m}^2

Ensures the patient continues to receive the insulin-sensitizing benefits of metformin while minimizing the risk of toxicity.

Key Concept

Metformin requires dose adjustment (maximum

1000\text{ mg/day}

) and closer monitoring when the estimated glomerular filtration rate (eGFR) falls between

30

and

45\text{ mL/min/1.73 m}^2

, and it must be discontinued entirely if the eGFR falls below

30\text{ mL/min/1.73 m}^2

Estimated Time:1m 0s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic