Iothalamic acid

Iothalamic acid Overview

Iothalamic acid (chemically designated as 5-acetamido-2,4,6-triiodo-N-methylisophthalamic acid; chemical formula C11H9I3N2O4) is a monomeric ionic triiodinated benzoic acid derivative. Chemically, it belongs to the class of organic compounds known as acylaminobenzoic acid and derivatives within the benzoic acids and derivatives sub-class of benzenoids. Structurally, it consists of a benzene ring substituted with a carboxylic acid group, three iodine atoms at positions 2, 4, and 6, an acetamido group, and a methylcarbamoyl group.

In diagnostic radiology and nephrology, Iothalamic acid functions as a water-soluble, nephrotropic high-osmolar X-ray contrast medium and diagnostic radiopharmaceutical (ATC code V08AA04 for watersoluble X-ray contrast media). Formulated as meglumine or sodium salts for intravascular injection, intravesical, or intrathecal administration (marketed under trade names such as Conray, Cysto-Conray, Vascoray, and the radioiodinated form Glofil-125), it is indicated for diagnostic radiologic visualization during excretory urography, cerebral angiography, peripheral arteriography, venography, arthrography, and computed tomography (CT) enhancement. The radioisotopic formulation Iothalamate Sodium I-125 is specifically indicated for evaluating glomerular filtration rate (GFR) to assess renal function in kidney disease. First approved by the US FDA in May 1962 under the brand Conray, its intravascular applications have largely been superseded by non-ionic low-osmolar contrast media to minimize osmolality-related side effects.

What Is Iothalamic acid and How Does It Work?

Iothalamic acid acts primarily through X-ray beam attenuation mediated by high-density iodine atoms, allowing radiopaque visualization of vascular structures, body cavities, and renal excretion pathways.

Its primary chemical, physiological, and diagnostic mechanisms include:

• Radiopaque X-Ray Attenuation: The three organically bound iodine atoms per molecule absorb X-ray photons via the photoelectric effect due to iodine’s high atomic number (Z = 53) and K-shell binding energy (33.2 keV). This radiopaque density blocks X-ray penetration, creating visual contrast between blood vessels or body lumens and surrounding soft tissues.
• Glomerular Filtration & Renal Excretion: Following intravascular administration, Iothalamate does not bind significantly to plasma proteins and is excreted almost entirely by glomerular filtration without tubular secretion or reabsorption, making it an ideal quantitative marker for precise glomerular filtration rate (GFR) measurement.
• High Osmolality Solution Dynamics: As a monomeric ionic compound, Iothalamate dissociates in aqueous solution into a contrast anion and a sodium or meglumine cation. This produces high solution osmolality (up to 4 to 6 times that of human blood plasma), drawing fluid from vascular endothelium and red blood cells, which accounts for systemic vasodilation, heat sensation, and osmotic nephrotoxicity.

Is Iothalamic acid FDA Approved?

Iothalamate Sodium and Meglumine formulations were approved by the US FDA in May 1962 under the brand name Conray. Its current approval status is FDA Approved (May 1962).

What Is Iothalamic acid Used For?

• Excretory urography and pyelography to evaluate renal structures, ureters, and bladder.
• Angiography, cerebral arteriography, peripheral arteriography, and venography.
• Contrast enhancement during computed tomography (CT) scans of the brain, liver, kidneys, pancreas, and retroperitoneum.
• Diagnostic quantitative determination of glomerular filtration rate (GFR) using Iothalamate Sodium I-125 (Glofil-125) in renal disease.
• Arthrography, direct cholangiography, and cystourethrography.

Before Taking Iothalamic acid: Contraindications & Precautions

Do not inject Iothalamic acid intrathecally or into the subarachnoid space when using standard intravascular concentrations, as direct central nervous system exposure can cause fatal convulsions and coma. Avoid intravascular injection in patients with known severe hypersensitivity to triiodinated contrast agents. Exercise extreme caution in patients with severe renal impairment, anuria, multiple myeloma, pheochromocytoma, or severe hyperthyroidism.

Who Should Not Take Iothalamic acid?

• Individuals with known severe hypersensitivity or prior immediate anaphylactoid reaction to Iothalamate or iodine compounds.
• Patients with pheochromocytoma (intravascular injection can precipitate severe hypertensive crises).
• Intrathecal administration of standard intravascular ionic contrast formulations.

Tell Your Doctor Before Taking Iothalamic acid

Inform your radiologist or physician if you have a history of severe asthma, food or drug allergies, chronic kidney disease, diabetes mellitus, heart failure, dehydration, multiple myeloma, or thyroid disease.

Iothalamic acid Dosage & Administration

Formulated as sterile aqueous solutions for injection containing 30% to 66.8% Iothalamate meglumine or sodium, or as Glofil-125 for GFR testing.

Standard Iothalamic acid Dosing

• Excretory Urography (Adults): Administered as 30 mL to 50 mL of concentrated solution (e.g., Conray 60% or Conray 400) intravenously as a rapid bolus.
• CT Scan Contrast Enhancement: Administered as 50 mL to 150 mL intravenously prior to and during imaging.
• GFR Determination (Glofil-125): Administered as a single intravenous or subcutaneous dose of 10 to 30 uCi followed by timed blood and urine sampling.

How Iothalamic acid Is Administered

• Administered intravascularly, intra-arterially, or locally into body cavities by trained radiology personnel.
• Maintain adequate patient hydration before and after contrast administration to prevent contrast-induced acute kidney injury.

Iothalamic acid Clinical Efficacy & Safety Profile

Clinical radiological studies establish that Iothalamate formulations provide excellent opacification of the urinary tract, vascular tree, and body cavities. In renal medicine, radioiodinated iothalamate (I-125) represents a gold-standard filtration marker for accurate GFR quantification. However, because of its ionic nature and high osmolality, intravascular Iothalamate produces a higher frequency of adverse physiological reactions such as intense heat sensations, flushing, and transient blood pressure drops compared to modern non-ionic contrast agents.

Iothalamic acid Side Effects & Safety Profile

Common reactions include transient heat sensation, facial flushing, metallic taste, nausea, vomiting, and localized pain at the injection site. Serious adverse risks include severe anaphylactoid shock, contrast-induced acute kidney injury (CI-AKI), cardiac arrhythmias, seizures, and pulmonary edema. Holds no FDA Black Box Warning.

Iothalamic acid Black Box Warning

Iothalamic acid currently carries no FDA Black Box Warning. Although it lacks the highest level of regulatory warning for life-threatening risks, clinicians and patients should remain cautious regarding potential adverse reactions. Standard monitoring and precautions for ionic contrast agents are still advised.

Common Iothalamic acid Side Effects

• Vascular / Systemic: Intense feeling of warmth or flushing throughout the body, transient sensation of heat in the pelvis, nausea, vomiting, metallic taste, and lightheadedness.
• Local: Transient burning pain or vein irritation at the intravenous injection site.

Serious Iothalamic acid Adverse Events

• Severe Hypersensitivity / Anaphylaxis: Immediate urticaria, laryngeal edema, severe bronchospasm, profound hypotension, and fatal anaphylactoid shock.
• Contrast-Induced Acute Kidney Injury (CI-AKI): Acute renal tubular necrosis, oliguria, and transient elevation of serum creatinine due to osmotic overload and renal medullary ischemia.
• Cardiovascular & Neurological Toxicity: Cardiac arrhythmias, severe hypotension, angina, or seizures if injected near cerebral vessels or accidentally intrathecally.

Managing Iothalamic acid Side Effects

Ensure emergency resuscitation equipment, oxygen, epinephrine, and intravenous fluids are immediately available in the radiology suite prior to contrast injection. Pre-procedure hydration reduces nephrotoxicity risks.

Iothalamic acid Drug Interactions & What to Avoid

Co-administration with nephrotoxic or biguanide medications requires specific clinical precautions.

Iothalamic acid Drug-Drug Interactions

• Metformin: Intravascular contrast-induced renal impairment can cause metformin accumulation, risking fatal lactic acidosis; metformin should be temporarily withheld at the time of the procedure.
• Nephrotoxic Drugs (e.g., Aminoglycosides, NSAIDs, Amphotericin B): Co-administration increases the risk of acute tubular necrosis and renal failure.
• Radioactive Iodine (I-131): Administration saturates thyroid iodine uptake capacity, interfering with diagnostic thyroid scans or radioiodine therapy for up to 2 to 6 weeks.

Iothalamic acid, Food & Alcohol

Maintain robust oral fluid intake prior to radiologic contrast procedures to ensure adequate hydration. Avoid alcohol consumption prior to imaging to prevent pre-existing dehydration.

Iothalamic acid: Missed Dose, Overdose & Storage

Administered as a single diagnostic procedure dose. Overdose causes extreme hyperosmolality and pulmonary edema. Store at controlled room temperature (15°C–25°C).

Missed Dose of Iothalamic acid

Not applicable; administered as a single, scheduled diagnostic procedure by healthcare professionals.

Iothalamic acid Overdose & Emergency

Intravascular overdose of high-osmolar contrast causes massive fluid shifts into the intravascular space, leading to acute hypervolemia, severe pulmonary edema, metabolic acidosis, renal failure, and cardiac arrest. Emergency management includes hemodialysis to remove the contrast agent, aggressive respiratory support, and diuretic therapy.

How to Store Iothalamic acid

Store sterile injection solutions at controlled room temperature between 15°C and 25°C (59°F to 77°F). Protect from light and freezing. Discard any unused open container portion immediately. Keep strictly out of reach of children.

Iothalamic acid Patient Management & Monitoring

Requires baseline renal function assessment and post-procedure hydration tracking.

Tests Before Starting Iothalamic acid

Baseline serum creatinine, estimated glomerular filtration rate (eGFR), hydration status evaluation, and history of prior contrast allergies.

Monitoring During Iothalamic acid Treatment

Continuous monitoring of vital signs (blood pressure, pulse, pulse oximetry) during and for at least 30 minutes following contrast injection to detect immediate hypersensitivity reactions.

Iothalamic acid Do’s and Don’ts

• Do maintain adequate hydration before and after receiving intravenous contrast.
• Do inform the radiologist immediately if you feel swelling in your throat, shortness of breath, or severe itching.
• Do not undergo contrast procedures without informing medical staff of pre-existing kidney disease or diabetes.
• Do not resume metformin therapy after contrast exposure until renal function is confirmed stable.

Frequently Asked Questions

References

• DrugBank Database – Iothalamic Acid Clinical Profile (DB09133)
• Classyfire Database – Acylaminobenzoic Acid / Benzenoids Taxonomy Profile
• US FDA Prescribing Information – Conray (Iothalamate Meglumine) Injection

Legal Disclaimer

The detailed medical and chemical information provided on this specific web page is intended strictly for educational and informational purposes regarding complex pharmacological mechanisms. It absolutely does not constitute professional medical advice, medical diagnosis, or specific treatment recommendations. Always consult a licensed healthcare provider before making any personal decisions regarding complex medical conditions, medication adjustments, or dietary changes.