Iodinated Contrast Media

Iodinated Contrast Media - Iodine Inside Basics

• Foundation: Derivatives of a tri-iodinated benzene core (e.g., $C_6H_3I_3 \cdot R_x$). Iodine provides radiopacity. Side chains (R) determine properties.
• Osmolality: Critical for safety. Plasma osmolality $\approx$ 290 mOsm/kg H₂O.
  • 📌 Mnemonic: More particles (Ionic) $\rightarrow$ Higher Osmolality $\rightarrow$ More reactions.

Comparison of ICM Types:

⭐ Non-ionic iso-osmolar contrast media (IOCM) like Iodixanol have osmolality closest to plasma (~290 mOsm/kg H₂O) and are associated with lower rates of adverse events and nephrotoxicity.

Iodinated Contrast Media - Contrast Cruise Control

• Administration & Distribution:
  • Typically IV; rapidly equilibrates from intravascular to entire extracellular fluid compartment.
  • Minimal protein binding.
• Elimination:
  • Primarily renal; excreted unchanged via glomerular filtration.
  • Half-life: ~1-2 hours in patients with normal renal function.
• 📌 Mnemonic: "I"odine "C"ontrast "M"edia: "I"ntravascular -> "C"ompartments (Extracellular) -> "M"icturition (Renal).

⭐ Iodinated contrast media are primarily excreted unchanged by glomerular filtration; thus, pre-existing renal impairment significantly prolongs their elimination and increases risk.

Iodinated Contrast Media - Reaction Red Flags

• Types of Reactions:
  • Idiosyncratic (Anaphylactoid): Unpredictable, not dose-related.
    • Immediate (<1 hr): Urticaria, angioedema, bronchospasm.
    • Delayed (>1 hr-1 wk): Skin rashes.
  • Non-idiosyncratic (Chemotoxic): Dose/concentration-dependent (nephrotoxicity, vasovagal).
• Severity & Symptoms:
  • Mild: Nausea, limited urticaria, pruritus.
  • Moderate: Diffuse urticaria, bronchospasm, mild hypotension.
  • Severe: Anaphylactic shock (hypotension, tachycardia), laryngeal edema. Adrenaline 0.3-0.5 mg IM (1:1000).
• Risk Factors: Previous ICM reaction, asthma, atopy.

  ⭐ Patients with a history of a moderate or severe allergic-like reaction to ICM have a ~5-fold increased risk of a repeat reaction; premedication is crucial.

• Prophylaxis (High-Risk):
  • Corticosteroids: Prednisolone 50mg PO (13h, 7h, 1h pre-ICM).
  • Antihistamines: Diphenhydramine 25-50mg IM/IV/PO (1h pre-ICM).
  • 📌 Premedicate High-Risk: Corticosteroids + Antihistamines (CAreful).

Iodinated Contrast Media - Kidney Care & Cautions

• Contrast-Induced Nephropathy (CIN): ↑SCr >0.5 mg/dL or >25% from baseline within 48-72h.
  • Risk Factors: CKD, diabetes, dehydration, ↑contrast volume, HOCM.
  • Prevention: IV hydration (isotonic saline), LOCM/IOCM, ↓volume, avoid NSAIDs.

    ⭐ The single most effective measure to prevent Contrast-Induced Nephropathy (CIN) is adequate periprocedural intravenous hydration with isotonic saline.

• Metformin: (Risk: Lactic Acidosis)
  • eGFR <30 mL/min: Stop.
  • eGFR 30-45 mL/min: Hold on day of procedure, restart 48h post if renal function stable.
  • eGFR >45 mL/min: Continue; assess individual risk.
• Thyroid Disease: Jod-Basedow (hyperthyroidism) / Wolff-Chaikoff (hypothyroidism).
• Pregnancy/Lactation: Use LOCM if essential; breastfeeding generally OK.
• Pheochromocytoma: Premedicate (alpha/beta blockers) for crisis prevention.

• Non-ionic, low/iso-osmolar agents (LOCM/IOCM) are safer, causing fewer adverse reactions.
• Contrast-Induced Nephropathy (CIN): ↑SCr >25% or >0.5 mg/dL in 48-72h; prevent with hydration, use LOCM/IOCM.
• Metformin: Hold 48h post-contrast if GFR <60 mL/min/1.73m² or AKI, risk of lactic acidosis.
• Anaphylactoid reactions are unpredictable; chemotoxic (e.g., CIN) are dose-dependent.
• Premedication (steroids) for prior severe reactions or significant asthma.
• Iodinated contrast can induce thyroid dysfunction (Jod-Basedow/Wolff-Chaikoff).