Iohexol

Nonionic iodinated contrast medium Radiocontrast agent

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.
Cat IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.
Horse IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.
Cattle IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.
Small Ruminants IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.
Rabbit IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.
Bird/Poultry IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.
Exotic/Other IV 300-600 mg iodine/kg (e.g., 1-2 mL/kg of 300 mgI/mL solution) Single dose Duration: Immediate imaging
Notes: For CT enhancement, administer as a bolus or infusion. Adjust dose based on imaging protocol.

Clinical Indications & Species Uses

General Indications
  • Radiographic contrast enhancement for CT, angiography, urography, myelography, arthrography, and other imaging studies
Dog (Canine)
  • Contrast-enhanced computed tomography (CT)
  • Angiography
  • Urography
  • Myelography
  • Arthrography
  • Fistulography
  • Gastrointestinal contrast studies
Cat (Feline)
  • Contrast-enhanced CT
  • Angiography
  • Urography
  • Myelography
  • Arthrography
  • Fistulography
  • Gastrointestinal contrast studies
Horse (Equine)
  • Contrast-enhanced CT
  • Angiography
  • Urography
  • Myelography
  • Arthrography
  • Tenography
  • Fistulography
Cattle (Bovine)
  • Contrast-enhanced CT
  • Urography
  • Myelography
  • Arthrography
  • Fistulography
Small Ruminants (Sheep / Goat)
  • Contrast-enhanced CT
  • Urography
  • Myelography
  • Arthrography
  • Fistulography
Rabbit & Small Mammals
  • Contrast-enhanced CT
  • Urography
  • Myelography
  • Arthrography
Avian & Poultry
  • Contrast-enhanced CT
  • Angiography
  • Urography
  • Gastrointestinal contrast studies
Exotic & Other Species
  • Contrast-enhanced CT
  • Angiography
  • Urography
  • Myelography
  • Arthrography

Pharmacology & Mechanism of Action

Drug Class: Nonionic iodinated contrast medium | Pharmacological Group: Radiocontrast agent

Mechanism of Action: Iohexol is a nonionic, water-soluble, iodinated radiographic contrast agent. It contains iodine atoms that attenuate X-rays, providing positive contrast in imaging. It does not undergo significant metabolism and is excreted unchanged by the kidneys. Its mechanism of action is purely physical: the high atomic number of iodine absorbs X-rays, allowing visualization of vascular structures, organs, and body cavities during imaging procedures.

Pharmacodynamics: Iohexol increases the radiopacity of the structures it fills or perfuses, allowing differentiation from surrounding tissues. It is nonionic and has low osmolality compared to ionic contrast agents, which reduces the risk of adverse reactions. It does not have significant pharmacological effects on the cardiovascular, nervous, or renal systems when used at recommended doses, but can cause transient hemodynamic changes if injected rapidly.

⚑ Pharmacokinetics Summary

Absorption: Not significantly absorbed after oral administration; used primarily for gastrointestinal studies. After intravascular injection, it distributes rapidly into the extracellular space.
Distribution: Distributes into the extracellular fluid compartment. It does not cross the intact blood-brain barrier but may enter the cerebrospinal fluid in myelography. It crosses the placenta in small amounts.
Metabolism: Iohexol is not metabolized to any significant extent. It is excreted unchanged by the kidneys.
Excretion: Excreted primarily by glomerular filtration. In animals with normal renal function, the majority is excreted within 24 hours. A small amount may be excreted in feces.
Half-Life: Dogs: approximately 1-2 hours; Cats: approximately 1-2 hours; Horses: approximately 1-2 hours; Cattle: approximately 1-2 hours.
Bioavailability: Not applicable for parenteral use; oral bioavailability is negligible.
Protein Binding: Negligible (<2%)

Available Formulations & Strengths

Injectable Solution 140 mgI/mL, 180 mgI/mL, 240 mgI/mL, 300 mgI/mL, 350 mgI/mL (IV, IA, IT, intracavitary, oral)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to iohexol or other iodinated contrast agents
  • Severe renal impairment (relative contraindication; use with caution)
  • Severe hepatic impairment (relative contraindication)
  • Dehydration (should be corrected before administration)
  • Thyrotoxicosis (relative contraindication)
  • Pregnancy (unless benefits outweigh risks)
Warnings & Clinical Precautions:
  • Use with caution in animals with pre-existing renal disease, cardiac disease, or seizures.
  • Ensure adequate hydration before and after administration.
  • Monitor for signs of anaphylactoid reactions, especially in animals with a history of allergies.
  • Avoid extravasation; may cause tissue irritation.
  • In myelography, use appropriate patient positioning and avoid rapid injection.
  • Use the lowest dose necessary for diagnostic quality.
  • In food animals, observe withdrawal times.

Adverse Effects & Reactions

Common:

  • Transient nausea or vomiting
  • Tachycardia or bradycardia
  • Hypotension or hypertension
  • Warmth or flushing
  • Pain at injection site

Serious / Severe:

  • Anaphylactoid reactions (hypotension, bronchospasm, angioedema)
  • Acute renal failure (especially in dehydrated or renally impaired animals)
  • Seizures (especially with myelography)
  • Cardiac arrhythmias
  • Pulmonary edema

Rare:

  • Thyroid dysfunction
  • Delayed hypersensitivity reactions
  • Neurotoxicity (with myelography)
  • Coagulation abnormalities

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Metformin Increased risk of lactic acidosis and renal failure; discontinue metformin before contrast administration and resume after 48 hours if renal function is normal. High
Nephrotoxic drugs (e.g., aminoglycosides, NSAIDs, amphotericin B) Additive nephrotoxicity; use with caution and monitor renal function. High
Beta-blockers May increase risk of anaphylactoid reactions and reduce compensatory cardiovascular response. Moderate
Interleukin-2 Increased risk of delayed reactions to contrast media. Moderate
Phenothiazines May lower seizure threshold; use with caution in myelography. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe hypotension
  • Cardiovascular collapse
  • Pulmonary edema
  • Renal failure
  • Seizures
  • Metabolic acidosis

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Maintain airway, breathing, and circulation. Administer intravenous fluids to maintain hydration and promote renal excretion. Monitor renal function and cardiovascular status. For severe reactions, administer epinephrine, corticosteroids, and antihistamines as needed. In cases of severe overdose, consider hemodialysis to remove the contrast agent.

Food Animal Withdrawal Times

πŸ₯© Meat: 0 daysπŸ₯› Milk: 0 daysπŸ₯š Eggs: 0 days

Iohexol is not approved for use in food animals in many countries; however, due to its rapid excretion, withdrawal times are generally short. Consult local regulations. In the US, no withdrawal period is required for approved uses, but extra-label use may require extended withdrawal times.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25Β°C, excursions permitted to 15-30Β°C).

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Protect from light. Do not freeze. Keep container tightly closed. Discard unused portions after opening.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in dogs and cats for contrast enhancement in CT, myelography, and other procedures. Not approved for food animals in the US.

Extra-Label (Off-Label) Use: In the US, iohexol is approved for use in dogs and cats for certain indications. Extra-label use in other species or for other indications is permitted under AMDUCA, provided a valid veterinarian-client-patient relationship exists and appropriate withdrawal times are observed.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Iohexol is a widely used nonionic contrast agent in veterinary imaging due to its low osmolality and favorable safety profile. It is essential to ensure adequate hydration before and after administration, especially in animals with renal compromise. Premedication with antihistamines or corticosteroids may be considered in high-risk animals, though routine use is not recommended. For myelography, careful patient positioning and slow injection are critical to minimize neurotoxicity. Always have emergency drugs (epinephrine, atropine, fluids) available during administration. In small animals, iohexol is commonly used for CT angiography and urography. In large animals, it is used for CT and arthrography. Doses should be adjusted based on the imaging modality and the iodine concentration of the formulation used.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)