Iohexol

Diagnostic Imaging

Iohexol is primarily used to enhance the clarity of images produced during diagnostic procedures. Because it contains iodine, it blocks X-rays, allowing specific areas of the body to stand out against surrounding tissues. It is used in several types of imaging, including:

• Angiography: Visualizing blood vessels in the heart, brain, or limbs to check for blockages or abnormalities.
• Computed Tomography (CT): Improving the detail of CT scans of the head, chest, abdomen, and pelvis.
• Urography: Examining the kidneys, ureters, and bladder.
• Myelography: Visualizing the spinal cord and nerve roots.
• Arthrography: Looking inside joints, such as the shoulder or knee.

Other Specialized Uses

In addition to being injected into the bloodstream or spine, iohexol may be used in other ways depending on the area being studied:

• Gastrointestinal Imaging: When taken by mouth or given rectally, it helps visualize the esophagus, stomach, and intestines.
• Hysterosalpingography: Used to examine the uterus and fallopian tubes.
• Body Cavity Imaging: Used to view various body cavities or ducts, such as the biliary tract or salivary glands.

Mechanism of Action

Iohexol belongs to a group of drugs known as radiopaque contrast media. It contains iodine, a substance that absorbs X-rays. When iohexol is present in the body, it blocks the passage of X-ray beams, causing the areas where the drug is concentrated to appear bright white on the resulting images.

This process provides a clear distinction between different types of tissues and structures that might otherwise look similar on a standard X-ray or CT scan. Doctors use this contrast to better visualize:

• Blood vessels and the heart
• The digestive system
• The urinary tract and kidneys
• The spinal cord and surrounding spaces
• Joints and other body cavities

The way the drug moves through the body depends on how it is administered. When injected into a vein or artery, it travels through the circulatory system to highlight blood flow and organs. If swallowed or given through a tube, it coats the lining of the stomach or intestines. Eventually, the body eliminates iohexol, primarily by filtering it through the kidneys and into the urine.

Common Side Effects

• Nausea or vomiting
• Headache or dizziness
• Flushing or a sudden feeling of warmth
• Metallic taste in the mouth
• Mild skin rash or itching
• Pain, coldness, or burning at the injection site

Serious Side Effects

Contact a healthcare provider immediately if you experience any of the following serious symptoms:

• Signs of a severe allergic reaction, such as hives, swelling of the face or throat, or difficulty breathing
• Chest pain, shortness of breath, or an irregular heartbeat
• Seizures, confusion, or extreme drowsiness
• Kidney issues, such as decreased urination or swelling in the feet and ankles
• Severe skin reactions, including blistering, peeling, or a red rash
• Vision changes or speech problems
• Neck stiffness or severe back pain following certain types of injections

Severe Allergic Reactions

Serious and potentially fatal hypersensitivity reactions, including anaphylaxis, may occur. These reactions can happen even without prior exposure to iodine-based contrast media. Medical facilities should be prepared to manage severe reactions with emergency equipment and trained personnel.

Kidney Function

Iohexol may cause a sudden decline in kidney function, known as contrast-induced nephropathy. The risk is higher for individuals with pre-existing kidney disease, diabetes, dehydration, or congestive heart failure. Adequate hydration is often necessary to help protect the kidneys.

Neurological Risks

When injected into the spinal canal (intrathecal use), iohexol carries a risk of serious neurological events, including seizures, coma, or paralysis. Precautions are taken during administration to prevent the contrast from reaching high concentrations in the brain.

Thyroid and Endocrine Concerns

In patients with hyperthyroidism, iodine contrast may trigger a thyroid storm. In infants, especially those born prematurely, exposure to iohexol can cause temporary hypothyroidism, which may require monitoring of thyroid function.

Cardiovascular and Other Risks

• Heart Events: Serious heart-related events, including cardiac arrest and arrhythmias, have been reported, especially in patients with underlying heart disease.
• Pheochromocytoma: Administration may cause a severe increase in blood pressure in patients with this adrenal tumor.
• Sickle Cell Disease: Contrast agents can promote the sickling of red blood cells in individuals with this condition.
• Myasthenia Gravis: Symptoms of muscle weakness may be aggravated.

Pregnancy

There are no adequate and well-controlled studies regarding the use of iohexol in pregnant women. While animal studies using high doses have not shown evidence of harm to the fetus or impaired fertility, these results do not always predict how a human will respond. Healthcare providers typically only use iohexol during pregnancy if the diagnostic benefit clearly outweighs any potential risks.

Breastfeeding

It is unknown if iohexol passes into human breast milk. Many similar contrast agents are known to be excreted in breast milk in very small amounts. If you are breastfeeding, consult your doctor to discuss the risks and benefits. Some patients may choose to temporarily stop breastfeeding for a short period after receiving the injection, though this should be discussed with a healthcare professional.

Available Forms

Iohexol is provided as a sterile solution for various diagnostic imaging applications. It is available in the following forms:

• Injectable Solution: Used for administration into veins, arteries, the spinal canal, or joint spaces.
• Oral Liquid: Used for imaging the digestive tract.
• Rectal Liquid: Used for imaging the lower gastrointestinal tract.
• Body Cavity Solution: Used for imaging areas such as the bladder, uterus, or biliary tract.

Strengths

The concentration of iohexol is typically expressed in milligrams of iodine per milliliter (mgI/mL). Common strengths include:

• 140 mgI/mL
• 180 mgI/mL
• 210 mgI/mL
• 240 mgI/mL
• 300 mgI/mL
• 350 mgI/mL

The solution is supplied in various sizes and containers, including single-use vials, glass bottles, and plastic bottles. It is also available in larger bulk containers for use in clinical settings, such as pharmacy bulk packages or imaging bulk packages. The specific concentration and volume used depend on the patient's age, body weight, and the type of imaging procedure being performed.

FDA Approval and Indications

Iohexol was first approved by the U.S. Food and Drug Administration (FDA) in the 1980s. It is classified as a nonionic, water-soluble, radiographic contrast medium. The FDA has approved iohexol for a wide range of diagnostic procedures, including:

• Angiography (imaging of blood vessels)
• Urography (imaging of the urinary tract)
• Computed tomography (CT) enhancement
• Myelography (imaging of the spinal cord)
• Arthrography (imaging of joints)

Safety Warnings and Regulatory Communications

The FDA requires specific labeling regarding the administration of iohexol. While it is approved for intrathecal (spinal) use at specific concentrations, the FDA warns that accidental administration of higher concentrations or incorrect formulations into the spinal canal can lead to serious adverse events, including seizures, cerebral hemorrhage, and death.

In recent years, the FDA has issued safety communications regarding the risk of thyroid dysfunction in pediatric patients. Following the use of iodinated contrast media like iohexol, newborns and children under three years old should be monitored for potential hypothyroidism or temporary decreases in thyroid hormone levels. This monitoring is typically recommended within three weeks of exposure.

There are currently no Risk Evaluation and Mitigation Strategies (REMS) programs required for iohexol. However, regulatory guidelines mandate that it must be administered by healthcare professionals in clinical settings equipped to handle emergency reactions, such as anaphylaxis or cardiac arrest, which can occur following contrast administration.

How Iohexol Works

Iohexol is a non-ionic, water-soluble contrast medium that contains iodine. When introduced into the body, the iodine atoms absorb X-rays as they pass through. This process creates a clear contrast between the area containing the agent and the surrounding tissues, allowing healthcare providers to see blood vessels, organs, and other internal structures more clearly on a monitor or film.

Common Uses

This agent is used for a wide variety of diagnostic tests, including:

• Angiography: Visualizing blood vessels and the heart.
• Computed Tomography (CT): Enhancing images of the head and body.
• Myelography: Imaging the spinal cord and nerve roots.
• Urography: Examining the kidneys, ureters, and bladder.
• Arthrography: Visualizing the joints.

Iohexol can also be used to examine the gastrointestinal tract or other body cavities during specialized imaging procedures.

Administration

Depending on the part of the body being examined, iohexol may be administered in several ways:

• Injection into a vein or artery.
• Injection into the spinal fluid (intrathecal).
• Oral ingestion (swallowed).
• Rectal administration.
• Direct instillation into body cavities or joints.