What are the guidelines for the safe administration of iohexol (iohexol, a non-ionic contrast agent)?

Safe Administration of Iohexol: Evidence-Based Guidelines

Iohexol is contraindicated only in patients with known hypersensitivity to iohexol itself, and can be safely administered with minimal precautions in most clinical scenarios, including patients with shellfish allergies, asthma, or those taking metformin. 1

Absolute Contraindications

• Known severe hypersensitivity to iohexol specifically is the only absolute contraindication per FDA labeling 1
• Significant volume overload (marked peripheral edema grade 3-4 or ascites) contraindicates plasma clearance measurement due to tracer sequestration causing GFR overestimation 2

Common Misconceptions That Should NOT Prevent Administration

The "Iodine Allergy" Myth

• Shellfish allergy is NOT a contraindication - the allergy is to tropomyosin, not iodine 2, 3
• Povidone-iodine allergy is NOT a contraindication - these are unrelated hypersensitivity mechanisms 2, 3
• The American College of Radiology explicitly states neither shellfish nor povidone-iodine allergy should be used as exclusion factors 2

Respiratory Disease

• Asthma and COPD are NOT contraindications - premedication is not recommended for these patients 2

Metformin Use

• No need to stop metformin before low-dose (5 mL) iohexol administration for GFR measurement 2

Dose-Dependent Safety Profile

Low-Dose Administration (GFR Measurement)

• 5 mL dose carries exceptionally low risk - one adverse event in 15,147 measurements (0.0066% rate) over 24 years 2
• Contains only 1-2 times daily recommended iodine intake, unlikely to saturate thyroid 2
• No washout period needed before radioactive iodine treatment, unlike high-dose imaging studies 2

High-Dose Administration (Imaging Studies)

• Use lowest possible dose in patients at risk for contrast-induced AKI 2
• Prefer iso-osmolar or low-osmolar agents over high-osmolar agents in high-risk patients 2
• Note: Evidence shows iohexol (low-osmolar) may have higher CIN risk than iodixanol (iso-osmolar) in patients with pre-existing CKD 2

Risk Stratification for Contrast-Induced AKI

High-Risk Patients Requiring Prophylaxis

• Pre-existing CKD (especially eGFR <60 mL/min) 2
• Diabetes with renal impairment 2
• Heart failure 2
• Repeated contrast exposure over short periods 2
• Concomitant nephrotoxins (NSAIDs, aminoglycosides) 2

Prophylactic Measures for High-Risk Patients

• Intravenous volume expansion is mandatory - use either isotonic sodium chloride or sodium bicarbonate 2
• Typical regimen: 3 mL/kg isotonic sodium bicarbonate over 60 minutes pre-procedure, then 1 mL/kg for 6 hours post-procedure 2
• Oral fluids alone are inadequate for prevention 2
• Target urine flow rate >150 mL/hour for 6 hours post-procedure 2

Prior Contrast Reactions

Switching Strategy (Preferred)

• Switching to a different chemical class provides better protection than premedication 3
• Iohexol is Group A (low-osmolar nonionic monomer); switching to Group C agents (like Gastrografin) avoids cross-reactivity 3
• For mild-to-moderate prior reactions, switching without premedication is recommended 3

When Premedication Is Considered

• Only for severe prior reactions when no alternative exists 3
• Glucocorticoid regimen starting 1 day before procedure, continuing up to 5 days 3
• High-certainty evidence for premedication efficacy is lacking - estimated NNT of 50,000 to prevent one fatal reaction 3
• No premedication substitutes for anaphylaxis preparedness - breakthrough reactions occur even with premedication 3

Patient Preparation for GFR Measurement

Timing Considerations

• Reschedule if acutely ill (infection, nausea, vomiting, diarrhea) 2
• Wait 7 days after prior iodinated contrast to ensure complete washout 2
• Perform testing in morning with patient neither dehydrated nor overhydrated 2

Medication Management

• Continue scheduled medications to determine GFR in steady-state 2
• Maintain regular diet before testing 2
• Avoid intermittent medications that could transiently affect GFR 2

Handling and Storage (Pharmacy Bulk Package)

• Single entry only using aseptic technique in laminar flow hood 1
• Complete fluid transfer within 8 hours of closure entry 1
• Temperature must not exceed 37°C after closure entry 1

Critical Pitfalls to Avoid

• Do not delay urgent procedures for premedication - benefit is uncertain and may cause harm through care delays 3
• Do not assume "iodine allergy" based on shellfish or povidone-iodine reactions 2, 3
• Do not use plasma clearance methods in volume-overloaded patients - use urinary clearance instead 2
• Do not continue ACE inhibitors/diuretics in poorly controlled diabetics undergoing high-dose contrast procedures, though recent small trials show no increased CIN risk with continuation 2