Iohexol

Approved indications (diagnostic/contrast use):

• Computed Tomography (CT) enhancement — head, neck, chest, abdomen, pelvis, and CT angiography (CTA).
• Intravascular angiography — coronary angiography, peripheral arterial angiography, visceral angiography, venography.
• Excretory urography / Intravenous urography.
• Myelography (intrathecal administration) — spinal canal and nerve root visualization (when an intrathecal, appropriate formulation and technique are used).
• Hysterosalpingography — evaluation of uterine cavity and tubal patency.
• Arthrography — joint space imaging.
• Intra-cavitary and intra-operative cholangiography in selected cases.

Clinically accepted off-label / specialized uses (practitioner discretion):

• Select interventional procedures and endovascular device imaging where a low-osmolar iodinated contrast is preferred.
• Contrast-enhanced mammography in some centers (institutional protocol dependent).

Formulations / concentrations: Common commercial concentrations include 240, 270, 300, 320, 350, 370 mg iodine/mL (choose concentration appropriate to imaging task and patient renal/cardiac status). Use warmed solution to reduce viscosity for injections.

General principles:

• Use the lowest concentration and volume that provides diagnostic quality.
• Tailor injection rate, volume and concentration to the modality (CT vs angiography), target vascular bed, and patient size.
• For intrathecal/myelographic use use only the product and concentration approved and validated for intrathecal administration and follow neuroradiology technique guidelines.

Typical adult dosing (examples — adjust per protocol and patient factors):

• CT (IV bolus, contrast enhancement): 1–2 mL/kg (commonly 50–150 mL total); injection rates 1–6 mL/s depending on scanner protocol and vascular phase required.
• CT angiography (CTA): 40–100 mL depending on scan length and injection rate (commonly 300–370 mg I/mL at 3–6 mL/s).
• Coronary angiography (intra-arterial): 3–8 mL per coronary injection; total and repeat injections per interventional protocol (commonly 300–370 mg I/mL).
• Peripheral, visceral angiography: 5–50 mL per injection depending on vessel and procedure.
• Excretory urography / IV urography: ~1 mL/kg (typical adult 50–100 mL of 270–300 mg I/mL).
• Hysterosalpingography: ~10–20 mL.
• Arthrography: 5–20 mL depending on joint.
• Myelography (intrathecal): typically 5–15 mL of appropriately diluted product per institutional myelography protocol (use only a formulation approved and recommended for intrathecal use and adhere strictly to aseptic/technique guidance).

Pediatrics:

• Dosing usually weight-based (commonly 0.5–2 mL/kg depending on indication and concentration), not to exceed the adult recommended total volume for the procedure. Neonatal and infant dosing must follow pediatric radiology protocols.

Elderly / frail patients:

• Start with conservative volume; reduce dose if renal function is reduced or if cardiac compromise is present. Monitor closely.

Renal impairment:

• Use minimal effective dose; consider alternative imaging if feasible. Ensure hydration and nephroprotection strategies (see Warnings & Precautions). In severe renal failure, consider dialysis timing if contrast is essential and dialysis planned.

Administration technique / practical points:

• Warm to body temperature; use dedicated IV line or power injector for bolus CT/angiography; flush with saline post-injection.
• Observe patient for immediate reactions during and for at least 30–60 minutes after administration (longer if history of allergy).
• For intrathecal use, strict aseptic technique, correct patient positioning, and appropriate CSF aspiration checks are required. Only trained clinicians should perform intrathecal injection.

Iohexol is a nonionic, monomeric, low-osmolar iodinated radiographic contrast medium. The iodine atoms in the molecule have a high atomic number, which strongly attenuates X-rays. When iohexol is introduced into blood or body cavities, iodine selectively increases the radiodensity of vascular structures, soft tissues, or cavities relative to surrounding tissues on X-ray/CT imaging, producing enhanced contrast and enabling visualization of anatomical details. Its nonionic, low-osmolar chemical structure reduces osmotic load and endothelial irritation compared with older high-osmolar ionic agents, improving hemodynamic and tolerability profiles.

• Absorption: Administered directly into circulation or body compartments — gastrointestinal absorption is not relevant.
• Distribution: Rapid distribution in extracellular fluid; volume of distribution approximates extracellular water. Protein binding is negligible.
• Metabolism: Not metabolized — chemically inert in vivo.
• Elimination: Primarily renal — excreted unchanged by glomerular filtration.
• Half-life: In subjects with normal renal function, plasma elimination half-life is approximately 1.5–3 hours (varies with dose and renal function).
• Excretion kinetics: >90% of administered dose generally recovered in urine within 24 hours in patients with normal renal function; elimination prolonged in renal impairment.
• Onset of effect: Immediate radiographic enhancement after injection.

Pregnancy: Adequate, well-controlled human data are limited. Iohexol crosses the placenta. Use only if the diagnostic information is essential and cannot be obtained by non-radiographic means; avoid elective contrast studies in early pregnancy. The risk–benefit decision should be individualized and documented.

Lactation: Small amounts may be excreted into breast milk; however, oral absorption by the infant is expected to be negligible. Most guidelines consider continuation of breastfeeding acceptable after administration. As a conservative option, some centers recommend expressing and discarding breast milk for up to 24 hours post-administration — this is optional and should be discussed with the mother.

• Primary therapeutic class: Iodinated radiographic contrast agent.
• Subclass: Nonionic, monomeric, low-osmolar iodinated contrast medium.

• Known hypersensitivity to iohexol or to any component of the formulation.
• History of severe immediate hypersensitivity or anaphylactoid reaction to iodinated contrast media (relative contraindication — requires specialist evaluation; alternative imaging modalities preferred).
• For intrathecal use: contraindicated if product is not specifically approved/formulated for intrathecal administration or in presence of active CNS infection (e.g., meningitis) unless clinically justified.
• Severe, uncontrolled hyperthyroidism (iodinated contrast can precipitate thyrotoxic crisis).
• Severe renal failure where contrast administration would produce unacceptable risk and no benefit is expected — use only if absolutely necessary and after expert consult.

Hypersensitivity and anaphylactoid reactions

• Reactions range from mild (nausea, urticaria) to severe (bronchospasm, laryngeal edema, hypotension, cardiac arrest). Have resuscitation equipment and trained personnel available. Consider premedication protocols for patients with prior mild–moderate reactions (institutional protocols vary).

Contrast-induced nephropathy (CIN) / acute kidney injury

• Risk factors: pre-existing renal impairment (especially diabetic nephropathy), dehydration, older age, heart failure, high total contrast dose, concomitant nephrotoxic drugs.
• Employ preventive strategies: assess renal function (eGFR/serum creatinine) prior to administration in at-risk patients, use the lowest effective dose, ensure adequate hydration, consider isotonic IV fluids, avoid or minimize nephrotoxic agents around the time of contrast.

Metformin:

• Risk of lactic acidosis if renal function declines after contrast. Current safe practice: withhold metformin at the time of contrast administration and for 48 hours afterwards in patients with risk factors or uncertain renal function; confirm renal function before restarting. Local institutional guidance may vary.

Thyroid dysfunction

• Iodinated contrast may exacerbate or precipitate thyrotoxicosis or hypothyroidism in susceptible patients — evaluate thyroid disease history.

Cardiovascular disease

• Use caution in patients with severe cardiac disease (arrhythmias, heart failure) who may have limited tolerance to volume shifts or adverse hemodynamic effects.

Intrathecal administration

• Intrathecal use carries risk of neurotoxicity and seizures if non-approved concentrations or agents are used. Use only contrast approved for intrathecal use and follow strict technique.

Extravasation

• Can cause local tissue irritation and pain; for intra-arterial/intravenous injections, monitor needle/catheter placement and stop injection immediately if extravasation suspected. Manage according to institutional extravasation protocol.

Monitoring

• Observe for immediate and delayed reactions; monitor renal function in at-risk patients for 48–72 hours.

Very common / common (procedure-related and immediate):

• Transient warmth or flushing sensation on injection.
• Mild nausea, vomiting.
• Headache, dizziness.
• Injection site pain or local discomfort.

Less common:

• Urticaria, pruritus, erythematous rash.
• Transient hypotension or hypertension.
• Transient changes in taste.

Serious but rare:

• Severe hypersensitivity/anaphylaxis (bronchospasm, angioedema, hypotension).
• Seizures (particularly with intrathecal administration or in patients with CNS disease).
• Pulmonary edema or respiratory compromise.
• Acute kidney injury / contrast-induced nephropathy.
• Cardiac arrhythmias or myocardial ischemia in predisposed patients.

Onset & dose dependence:

• Most immediate reactions occur within minutes of administration; delayed cutaneous reactions may appear hours to days after exposure. Risk of nephrotoxicity increases with higher total iodine dose and pre-existing renal dysfunction.

• Metformin: See section 8 — withhold metformin around the time of contrast as above.
• Nephrotoxic agents (e.g., aminoglycosides, amphotericin B, high-dose NSAIDs, certain chemotherapeutic agents): concomitant use increases risk of renal injury; minimize exposure where possible.
• Beta-blockers / ACE inhibitors: May blunt physiologic response during anaphylactoid reactions and complicate management; not absolute contraindication but be aware.
• Diuretics: May exacerbate volume depletion and increase renal risk if patient is not adequately hydrated.
• Interleukin-2 and other immunomodulators: Higher risk of delayed cutaneous or systemic reactions has been reported.
• Thyroid-related medications / iodine exposure: Prior or concurrent exposure to iodine (e.g., some medications or topical antiseptics) may interact with thyroid status.

No clinically relevant CYP450 enzyme interactions (iohexol is not metabolized).

(Generalized, practice-oriented summaries consistent with contemporary radiology safety guidance)

• Pre-procedure renal screening: Guidelines emphasize obtaining baseline renal function (eGFR) in patients with risk factors; avoid routine screening in low-risk outpatients depending on institutional policy.
• Hydration & nephroprotection: Strong emphasis on periprocedural volume optimization (isotonic saline) for patients at risk of CIN and limiting contrast volume.
• Metformin management: Continued recommendation to withhold metformin at contrast administration in patients with renal impairment or uncertain renal status and to reassess kidney function prior to resuming metformin (commonly 48 hours).
• Use of lower iodine concentration / volume and modern protocols: Protocol optimization (lower concentration, tailored injection rates) and iterative CT reconstruction techniques reduce required iodine dose while preserving diagnostic quality.
• Alternative agents and strategies: For patients with prior severe contrast allergy, consider alternative imaging modalities or premedication protocols; for those with severe renal failure, use multidisciplinary decision-making and dialysis planning if indicated.

• Recommended storage temperature: 20°C to 25°C (68°F–77°F); short excursions permitted per manufacturer guidance (commonly up to 30°C).
• Do not freeze. If product has been frozen, do not use — discard.
• Protect from excessive light and store in original container until use.
• Single-use vials/bottles: Discard any unused portion after puncture according to aseptic technique and institutional infection-control policy. Multi-dose containers (if applicable) must follow manufacturer recommendations.
• Handling: Warm to body temperature before high-flow/power injections to reduce viscosity; inspect for particulate matter, discoloration, or container damage prior to use — do not use if present.
• Reconstitution: Not applicable (iohexol is provided ready-to-use); follow dilution guidance only if explicitly recommended in product literature for specific intrathecal or specialized uses.