Diagnostic Contrast Agents and Related Substances

Safety

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Medication used in diagnostic radiology includes:

• Barium sulphate suspension.
• Non-ionic contrast media, e.g.:
  • iohexol, or
  • iopamidol, or
  • iopromide.
  • Ioversol.

SAFETY

• The overall rate of adverse reactions is estimated to be less than 1 in 100¹ when using non-ionic contrast media and serious allergic reactions are even less common (about 1 in 2000²). 
• Contrast media-associated fatality is rare, estimated to be 2 per million injections.³
• Management of any reaction depends on its severity.
• Life-threatening acute cardiopulmonary collapse should be treated according to guidelines for cardiopulmonary resuscitation. See chapter: Emergencies and injuries.
• Moderate and severe reactions may be associated with bronchospasm and wheeze, stridor, hypotension, and loss of consciousness.
• Stop the infusion of contrast agent and start treatment as for anaphylaxis including adrenaline, oxygen (if indicated), intravenous fluids, and antihistamines. See Angioedema and Anaphylaxis/anaphylactic shock.

Iodine Allergy: (Z91.0)

Patients allergic to iodine are at an increased risk of adverse drug reactions when exposed to iodine-containing contrast media and patients who report previous allergic reactions too contrast agents should be carefully evaluated as to the need for investigation. If the investigation is considered essential, the patient should be pre-treated with steroids and antihistamines before proceeding.

• Corticosteroids (intermediate-acting) e.g.:
  • Prednisone, oral, 50 mg given 13 hours, 7 hours, and 1 hour before the procedure.

LoE:II⁴

Contrast induced nephrotoxicity (CIN) 

• CIN is an important consideration; it may result in permanent renal impairment with significant effects on longevity.
• This is particularly important in an environment with limited access to renal replacement therapy.
• Before referring any patient for an investigation involving contrast use, carefully weigh up the individuals' potential risk of CIN against potential benefits (the likelihood of detecting a condition for which a significant therapeutic intervention is available).
• CIN is variously defined as either a 25% or a 50% rise on pre-contrast creatinine levels, or an absolute creatinine increase of more that 25 micromol/L.
• CIN is rare in individuals with normal renal function ^5,6.
• Factors that increase the risk of CIN include: diabetes, pre-existing renal impairment, age >75 years, anaemia, cardiac failure, hypotension and the volume of contrast media injected ^7,8
• The probability of developing a 25% rise in creatinine after cardiac catheterisation in patients given 200 mL of non-ionic contrast media is linked to co-morbidity ⁷:

CIN risk	None	Anaemia	>75 yrs	CCF or low BP	>1 risk factor
No diabetes
eGFR >60	7.5%	7.5%	7.5%	15%	15%
eGFR 40-60	7.5%	15%	15%	15%	15%
eGFR 20-40	7.5%	15%	15%	15%	25%
eGFR <20	15%	15%	25%	25%	25%
Diabetes
eGFR >60	7.5%	15%	15%	15%	25%
eGFR 40-60	15%	15%	15%	25%	25%
eGFR 20-40	15%	25%	25%	25%	25%
eGFR <20	15%	25%	25%	25%	55%

 The probability of needing dialysis after cardiac catheterisation correlated with the risk of CIN ⁷:

CIN risk	7.5%	15%	25%	55%
Dialysis risk	0.04%	0.12%	1.1%	13%

Reducing the risk of developing CIN 

• There is no clear evidence that any specific medication is protective against the development of CIN. 
• However, meticulous attention to fluid balance is important in patients at higher risk, as dehydration increases the risk of CIN.
• Patients on metformin should be monitored for deterioration in renal function post procedure as there is a small risk of precipitating lactic acidosis. 
• In high risk patients it may be advisable to omit metformin for 48 hours after contrast injection while monitoring serum creatinine. 

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Standard Treatment Guidelines and Essential Medicines List for South Africa, Hospital Level, Adults 2024 Edition