Medications to Discontinue Before CT Scan with IV Contrast
For patients scheduled for CT A/P with IV contrast, metformin should be discontinued at the time of the procedure and withheld for 48 hours afterward, while other nephrotoxic medications (NSAIDs, aminoglycosides, amphotericin B) should be stopped 48 hours before the procedure when possible. 1, 2
Metformin Management
When to Stop:
- Timing: Discontinue metformin at the time of or prior to the IV contrast procedure 3
- Duration: Withhold for 48 hours after the procedure 1, 2, 3
When to Restart:
- For patients with low risk of nephrotoxicity: Metformin can be restarted after 48 hours without the need for renal function assessment 1
- For patients with high risk of nephrotoxicity: Metformin should only be reinstituted after renal function has been reevaluated and found to be normal 1, 3
- eGFR threshold: Only restart when eGFR is confirmed to be > 40 mL/min/1.73 m² 2
Other Medications to Discontinue
The following medications should be stopped 48 hours before the procedure when possible 2:
- NSAIDs (ibuprofen, naproxen, etc.)
- Aminoglycosides (gentamicin, tobramycin, etc.)
- Amphotericin B
Risk Assessment for Contrast-Induced Nephropathy
High-Risk Patients:
- Age > 60 years
- Pre-existing renal disease or impairment
- Diabetes mellitus
- History of hypertension requiring medical therapy
- Use of metformin/metformin-containing medications
- eGFR < 60 mL/min/1.73 m²
- Creatinine > 13 mmol/L (1.5 mg/dL) 1, 2
Special Considerations:
- For patients with eGFR between 30-60 mL/min/1.73 m², metformin must be stopped at the time of contrast administration 3
- For patients with history of liver disease, alcoholism, or heart failure, additional caution is required 3
- For patients receiving intra-arterial iodinated contrast, stricter precautions apply 3
Preventive Measures for High-Risk Patients
For patients at high risk of contrast-induced nephropathy:
- Administer intravenous hydration with isotonic saline (0.9% NaCl) at 1 mL/kg/h for 6-12 hours before and 24 hours after the procedure 2
- Consider using iso-osmolar or low-osmolar contrast media 2
- Minimize contrast volume (aim for <30 mL if possible) 2
Common Pitfalls and Caveats
Unnecessary withholding: There is no scientific justification for withholding metformin for 48 hours before contrast administration 4. The risk is after contrast exposure.
Failure to restart medication: Patients may remain off metformin unnecessarily if follow-up renal function is not assessed in a timely manner.
Overestimation of risk: The incidence of contrast-induced nephropathy in diabetic patients without prior renal failure is extremely low (0% in some studies) 5.
Lactic acidosis risk: The primary concern with metformin and contrast media is not direct interaction but the potential for lactic acidosis if contrast causes renal failure and metformin continues to be taken 4.
Ignoring alternative glucose control: During the period when metformin is withheld, an alternative glucose-controlling medication should be considered 1.
By following these guidelines, the risk of contrast-induced nephropathy and associated complications like lactic acidosis can be minimized while ensuring appropriate diagnostic imaging.