Do I need to repeat blood work before starting Janumet (sitagliptin and metformin)?

Blood Work Requirements Before Starting Janumet

Blood work is not required before starting Janumet (sitagliptin/metformin) if you have had recent laboratory tests showing normal kidney function, but renal function should be assessed after starting the medication.

Baseline Assessment Requirements

When starting Janumet (sitagliptin/metformin combination), the following laboratory assessments should be considered:

Required Tests

• Renal function: eGFR should be checked before initiating therapy
  • Metformin is contraindicated if eGFR is less than 30 mL/min/1.73 m² 1
  • Dose adjustment is required if eGFR is between 30-45 mL/min/1.73 m² 1

Timing of Tests

• If you've had renal function tests within the past 3-6 months showing normal kidney function, you do not need to repeat them before starting Janumet
• If your last renal function test was more than 6 months ago or if you have risk factors for kidney disease, new baseline tests should be obtained

Monitoring After Starting Janumet

• Renal function: Should be monitored at least annually in all patients taking metformin, or more frequently (every 3-6 months) if eGFR <60 mL/min/1.73 m² 2
• Follow-up testing: After starting Janumet, renal function should be monitored:
  • Within 1-2 weeks if baseline kidney function is borderline
  • Within 3 months for all patients

Special Considerations

Contrast Studies

• If you are scheduled for radiologic studies with contrast:
  • Janumet should be temporarily discontinued at the time of or prior to the procedure if eGFR is between 30-60 mL/min/1.73 m² 1
  • Renal function should be re-evaluated 48 hours after the imaging procedure 3
  • Janumet can be restarted if renal function is stable 3

Risk Factors Requiring More Careful Monitoring

• Age >65 years
• History of renal impairment
• Heart failure
• Liver disease
• Alcohol use disorder
• Use of medications that may affect kidney function

Common Pitfalls to Avoid

1. Failing to check baseline renal function: Metformin is primarily cleared by the kidneys, and impaired renal function increases the risk of lactic acidosis

2. Not monitoring for signs of lactic acidosis: Be aware of symptoms such as muscle pain, difficulty breathing, unusual sleepiness, or stomach discomfort 1

3. Overlooking drug interactions: Certain medications may interact with Janumet and affect kidney function or increase metformin levels

4. Ignoring the need for periodic monitoring: Regular assessment of renal function is essential, especially in patients with risk factors for kidney disease

Remember that Janumet combines sitagliptin and metformin in a fixed-dose combination tablet that has been shown to be bioequivalent to taking the individual components separately 4, but the metformin component requires careful monitoring of renal function.