Generic Name

Iohexol

Mechanism

Iohexol is a non‑ionic, low‑osmolar iodinated contrast agent.
• X‑ray attenuation: The high‑atomic‑number iodine atoms absorb photons, increasing radiodensity of iodinated tissues.
• Vascular delineation: When injected intravenously, it transiently concentrates within the vascular system, enhancing visualization of blood vessels, organs, and pathologic lesions during CT or angiographic studies.
• No receptor binding: Its effect is purely physical (photonic attenuation), not mediated by pharmacologic receptors.

Pharmacokinetics

• Absorption: Rapid, complete distribution following IV or intra‑arterial injection.
• Plasma protein binding: Negligible; exists largely in a free form.
• Distribution: Widely disseminates into the extracellular fluid space.
• Metabolism: Not metabolized; excreted unchanged.
• Elimination: Primarily renal via glomerular filtration.
• Half‑life: ~1–1.5 h in patients with normal renal function.
• Clearance: Depends on glomerular filtration rate (GFR); marked reduction in CKD.
• Special Populations: Clearance is markedly reduced in severe renal impairment; dosing adjustments or avoidance may be necessary.

Indications

• Computed Tomography (CT): Contrast‑enhanced abdominal, chest, neuro‑, and vascular studies.
• Angiography: Baseline and diagnostic vascular imaging.
• Arteriography: Pulmonary, cerebral, and peripheral vascular evaluations.
• Guided Procedures: Interventional radiology (e.g., embolization, stenting).

Contraindications

Dosing

• Standard IV Dose
• 1–2 mL/kg (up to 200 mL for adult CT) for non‑contrast‑enhanced CT; adjust for body weight or specific imaging protocol.
• Angiography
• 10–20 mL/kg depending on vascular territory and desired vascular opacification.
• Administration Rate: 3–5 mL/sec for CT; lower rates for intra‑arterial injections to minimize acute pressure changes.
• Pre‑Medication (if indicated):
• Oral: 4–6 h prior: diphenhydramine 25–50 mg + prednisone 10–20 mg.
• Intramuscular: corticosteroid 100 mg of methylprednisolone.
• Hydration: 30 min before and after administration (oral if tolerated or IV saline 1 mL/kg/hr).
• Monitoring: Vital signs during injection; observe for signs of hypersensitivity (rash, bronchospasm, hypotension).

Adverse Effects

*Patients with a previous mild reaction may tolerate subsequent doses with appropriate pre‑medication.*

Monitoring

1. Renal Function
• Baseline serum creatinine/eGFR; recheck 24–48 h post‑contrast.

2. Vital Signs
• Blood pressure, heart rate, oxygen saturation during infusion.

3. Symptom Check
• Watch for nausea, dizziness, flushing, chest tightness.

4. Hydration Status
• Urine output; avoid over‑diuresis in patients with hepatic or cardiac dysfunction.

Clinical Pearls

• Pre‑Hydration is the gold standard: Administer 1 L of isotonic saline 30 min before contrast to significantly lower CIN risk.
• Limit cumulative exposure: Keep total daily iodine dose < 1.5 g (≈250 mg I/kg) to avoid nephrotoxicity in patients with borderline kidney function.
• Low‑osmolarity advantage: Iohexol’s low osmolality (< 600 mOsm/kg) reduces the incidence of adverse hemodynamic responses compared with older high‑osmolar agents.
• Track prior reactions meticulously: Document any contrast reaction in the patient’s chart; use a clear “contrast allergy” alert for future imaging.
• Use in pregnancy cautiously: Although no teratogenic effects have been proven, avoid elective contrast CT in the first trimester when alternate modalities (MRI, ultrasound) are feasible.
• Drug interaction check: Metformin clearance may decrease if significant renal impairment develops post‑contrast; hold Metformin if eGFR falls <30 mL/min/1.73 m².
• Special populations: In patients with end‑stage renal disease on dialysis, administer *only* if no alternative imaging is available, and preferably after a dialysis session to hasten clearance.

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