Iohexol

MECHANISM OF ACTION

Iohexol acts as a non-ionic, iodinated radiographic contrast agent whose mechanism is based on physical enhancement of X-ray imaging rather than pharmacologic receptor activity. It contains iodine atoms with a high atomic number that effectively absorb and attenuate X-rays when exposed during imaging procedures. After administration, iohexol distributes within blood vessels, body fluids, or specific compartments such as the cerebrospinal space, increasing the radiodensity of these areas.

PHARMACOKINETICS

Absorption

Iohexol is not absorbed in the traditional sense when administered intravascularly, as it is directly introduced into the bloodstream, resulting in immediate systemic availability. When given orally or rectally, absorption from the gastrointestinal tract is minimal, with most of the administered dose remaining within the lumen and being excreted unchanged.

Distribution

Iohexol has a low volume of distribution, approximately 0.2–0.3 L/kg, which is close to the extracellular fluid volume.

Metabolism

Iohexol undergoes negligible metabolism in the body. It is not significantly biotransformed by the liver or other tissues and remains largely in its unchanged form throughout its circulation.

Elimination

Iohexol is eliminated primarily by the kidneys through glomerular filtration in an unchanged form. It is rapidly cleared from the bloodstream, with most of the administered dose excreted in the urine within 24 hours in individuals with normal renal function.

PHARMACODYNAMICS

Iohexol produces its effects through physicochemical interactions with X-rays rather than receptor-mediated pharmacologic activity. As a non-ionic, iodinated compound, it increases the radiodensity of the structures into which it is distributed by absorbing X-rays due to the high atomic number of iodine.

ADMINISTRATION

Iohexol is administered under medical supervision and the route depends on the type of diagnostic procedure being performed. It is most commonly given intravenously (IV) for contrast-enhanced CT scans and angiography, allowing rapid distribution within the vascular system.

DOSAGE AND STRENGTH

Iohexol is available in several iodine concentration strengths, commonly expressed as 140 mg I/mL, 240 mg I/mL, 300 mg I/mL, and 350 mg I/mL, with the choice of formulation depending on the imaging procedure and required level of radiographic contrast.

DRUG INTERACTIONS

Iohexol has relatively few true pharmacologic drug–drug interactions because it is not metabolized and does not act on receptors; however, several clinically important interactions and precautions are recognized. Concurrent use with nephrotoxic drugs such as aminoglycosides, amphotericin B, vancomycin, NSAIDs, or high-dose diuretics may increase the risk of contrast-induced nephropathy, especially in patients with pre-existing renal impairment.

FOOD INTERACTIONS

Iohexol has no clinically significant direct food–drug interactions, since it is a non-absorbed, non-metabolized iodinated contrast agent used primarily for diagnostic imaging. Food intake does not alter its pharmacokinetics or imaging effectiveness when it is administered intravenously or intra-arterially.

CONTRAINDICATIONS

Iohexol is contraindicated in patients with a known history of severe hypersensitivity reactions to iohexol or other iodinated contrast media. It should not be used in patients with overt hyperthyroidism or untreated thyrotoxicosis, as iodinated contrast can potentially exacerbate thyroid dysfunction.

SIDE EFFECTS

• Hypersensitivity reactions: rash, itching, urticaria 

• Severe allergic reactions (rare): anaphylaxis, bronchospasm, angioedema 

• Injection site reactions: pain, warmth, swelling, or inflammation 

• Nausea and vomiting 

• Feeling of warmth or flushing during injection 

• Headache or dizziness 

• Cardiovascular effects (rare): hypotension, arrhythmias.

OVER DOSE

Overdose of Iohexol is rare because it is administered in controlled radiology settings, but excessive administration can lead to clinically significant toxicity. The primary concern is renal toxicity (contrast-induced nephropathy) due to a high iodine load, which may result in reduced urine output, elevated serum creatinine, and acute kidney injury, especially in patients with pre-existing renal impairment.

TOXICITY

Toxicity from Iohexol is primarily related to its high iodine load and osmolality effects rather than direct biochemical toxicity. The most clinically significant toxic effect is contrast-induced nephrotoxicity, which can lead to acute kidney injury, especially in patients with pre-existing renal impairment, diabetes mellitus, dehydration, or concurrent use of nephrotoxic drugs.