Indocyanine Green (ICG): The Ultimate Guide
What Is Indocyanine Green?
Indocyanine Green (ICG), or indocyanine green dye, is a water-soluble, fluorescent tricarbocyanine dye with a peak spectral absorption at 800-810 nm in blood plasma.
First approved by the FDA in 1956, ICG is a vital diagnostic and imaging agent used across medical specialties.
Its unique properties, including rapid hepatic clearance and near-infrared (NIR) fluorescence, make it indispensable in surgeries, ophthalmic imaging, and liver function testing.
Understanding ICG’s chemical structure and regulatory status is crucial for API importers and compounding pharmacies to ensure compliance and meet the demands of healthcare providers.
Does Indocyanine Green Contain Iodine?
One of the most frequently asked questions by compounding pharmacists and patients is: “Does ICG API contain iodine?” The answer is nuanced.
Iodine Content in ICG API:
ICG’s chemical structure includes iodine atoms: specifically, two iodine molecules per cyanine dye molecule.
However, the iodine content is minimal (approximately 5% by molecular weight), and clinical studies show it rarely triggers iodine allergies.
Unlike contrast agents used in CT scans (which contain high iodine loads), ICG’s iodine is tightly bound to its cyanine structure, reducing the risk of allergic reactions.
Clinical Implications:
- Allergy Risk: Patients with severe iodine allergies should still exercise caution, but ICG is generally considered safe for those with mild iodine sensitivities.
- Pharmaceutical Grade: Reputable API suppliers ensure that ICG meets strict purity standards (e.g., USP, EP, or JP) with minimal contaminants, including free iodine.
For compounding pharmacies, this means Indocyanine Green API can often be used in formulations for patients with iodine allergies, provided proper screening and dilution protocols are followed.
What Is Indocyanine Green Used For?
Indocyanine green (ICG) is a near-infrared (NIR) fluorescent dye with diverse medical applications, primarily leveraging its ability to emit fluorescence when excited by NIR light and its preferential accumulation in specific tissues. Here’s a structured overview of its key uses:
1. Ophthalmology: Choroidal and Retinal Angiography
ICG is critical in indocyanine green angiography (ICGA), which is used to visualize deeper ocular structures, such as the choroid (the layer of blood vessels beneath the retina), and to diagnose conditions not fully assessed by fluorescein angiography (FA). Common applications include:
- Age-related macular degeneration (AMD): Detecting choroidal neovascularization (abnormal blood vessel growth).
- Polypoidal choroidal vasculopathy (PCV): Identifying characteristic polypoidal lesions in the choroid.
- Central serous chorioretinopathy (CSCR): Evaluating fluid accumulation under the retina.
- Choroidal tumors or inflammation: Assessing abnormal blood flow in these conditions.
2. Oncology & Surgical Guidance
ICG’s accumulation in tumor tissues (due to increased vascular permeability and blood flow) enables image-guided surgery:
- Tumor Detection: Real-time visualization of solid tumors (e.g., breast, gastrointestinal, head/neck, melanoma) during resection to improve margins.
- Sentinel Lymph Node (SLN) Mapping: Identifying lymph nodes draining tumors to assess metastasis spread.
- Metastasis Detection: Highlighting small metastatic deposits in lymph nodes or distant sites.
3. Dermatology: Vascular Lesion Assessment
ICG highlights abnormal cutaneous blood vessels, aiding in the diagnosis and treatment planning of:
- Port-wine stains (capillary malformations).
- Hemangiomas and telangiectasias (enlarged surface blood vessels).
- It may guide laser therapy by targeting these vessels.
4. Cardiology: Myocardial Perfusion & Vascular Imaging
While less common than other agents, ICG is used to:
- Evaluate myocardial perfusion during cardiac catheterization (assessing blood flow to the heart muscle).
- Assess coronary artery bypass graft (CABG) patency by visualizing the graft blood flow.
5. Liver Function Assessment
ICG is metabolized by the liver and excreted into bile. Measuring its clearance (ICG clearance test) evaluates hepatic function, aiding in:
- Preoperative risk assessment for liver surgery (e.g., resection feasibility).
- Monitoring liver disease progression (e.g., cirrhosis, hepatitis).
6. Intraoperative Vascular Imaging
ICG guides complex surgeries by visualizing blood flow:
- Liver Resection: Identifying segmental hepatic vessels to preserve healthy tissue.
- Free Flap Reconstruction: Ensuring adequate perfusion of transplanted tissue (e.g., breast, head/neck reconstructions).
- Bleeding Vessel Detection: Locating occult vascular leaks during procedures.
7. Research Applications
ICG is used in preclinical studies to:
- Investigate microcirculation in organs (e.g., the brain and kidneys).
- Evaluate drug delivery systems or nanotechnology-based contrast agents.
Safety Considerations
ICG is generally well-tolerated; however, it contains iodine, so it is contraindicated in patients with severe iodine allergies. Mild side effects (e.g., rash, nausea) are rare.
How Does Indocyanine Green Work?
Understanding the mechanism of ICG is key to optimizing its use in APIs and formulations. Here’s a breakdown:
1. Absorption and Excitation
When injected intravenously (IV), ICG binds to plasma proteins, primarily albumin, thereby restricting its distribution to the bloodstream. It absorbs NIR light (with a peak absorption at ~780 nm), exciting its electrons to a higher energy state.
2. Fluorescence Emission
As electrons return to their ground state, ICG emits light at a longer wavelength (~830 nm)—a process called fluorescence. This NIR light penetrates deeply into tissues (up to 2–3 mm), allowing for the imaging of subsurface structures.
3. Tissue-Specific Accumulation
ICG’s distribution depends on blood flow and vascular permeability:
- Choroid/Retina: High blood flow in the choroid makes it ideal for ophthalmic imaging.
- Tumors: The EPR effect causes ICG to accumulate in cancerous tissues due to leaky blood vessels.
- Liver: Hepatocytes (liver cells) rapidly take up ICG, facilitating assessment of liver function.
4. Metabolism and Excretion
ICG is metabolized in the liver by cytochrome P450 enzymes and excreted into bile, primarily via the feces. Its half-life is ~3–5 minutes, minimizing systemic exposure.
For formulators: ICG’s rapid clearance means formulations must be used immediately after reconstitution (unless stabilized). Compounding pharmacies should follow strict protocols to maintain potency.
Indocyanine Green Dosage and Administration
Dosage varies depending on the application, patient weight, and route of administration.
Below are guidelines for common uses:
1. Ophthalmic Angiography
- Dose: 25 mg (0.5 mL of 5 mg/mL solution) injected IV over 10–20 seconds.
- Administration: Followed by fundus photography and NIR imaging within 5–10 minutes.
2. Oncologic Surgery
- Dose: 0.25–0.5 mg/kg IV, administered 10–20 minutes before surgery.
- Administration: Continuous imaging during resection to guide tumor removal.
3. Liver Function Testing
- Dose: 0.5 mg/kg IV, injected as a bolus.
- Administration: Blood samples were taken at 5, 10, 15, and 20 minutes post-injection to calculate the clearance rate.
4. Compounding Pharmacy Considerations
- Reconstitution: ICG powder must be reconstituted with sterile water for injection (SWFI) according to the manufacturer’s guidelines (typically 2.5 mg/mL or 5 mg/mL).
- Stability: Reconstituted solutions are stable for 6–12 hours at room temperature (avoid prolonged exposure to light).
- Patient-Specific Dosing: Adjust the dose based on age, weight, and condition (e.g., reduce the dose in cases of renal or hepatic impairment).
For importers: Pharmaceutical-grade ICG APIs must meet USP/EP purity standards to ensure accurate dosing in compounded formulations.
What Are the Side Effects of Indocyanine Green?
ICG is generally safe, with adverse effects occurring in <1% of patients:
Mild: Nausea, itching, or urticaria.
Severe (Rare): Anaphylaxis, hypotension, or tachycardia.
Risk factors include iodine allergy, hepatic impairment, and pregnancy (see safety section below).
To minimize contamination risks, compounding pharmacies must provide clear labeling and consistently follow handling protocols.
Indocyanine Green Precautions and Drug Interactions
Precautions:
- Iodine Allergies: Screen patients with a history of iodine sensitivity and consider skin testing if necessary.
- Pregnancy/Lactation: Limited safety data (see “Is ICG Safe During Pregnancy?” below).
- Liver/Kidney Disease: Reduce the dose in patients with impaired hepatic or renal function (ICG is metabolized and excreted by these organs).
- Light Sensitivity: ICG solutions degrade in light—store reconstituted formulations in dark vials.
Drug Interactions:
- Bilirubin: High bilirubin levels may interfere with ICG clearance measurements (liver function tests).
- Beta-Blockers: May reduce ICG clearance (theoretical risk; monitor liver function).
Cholestyramine may delay hepatic uptake.
- Valproic acid can displace ICG from plasma proteins, altering fluorescence.
Pharmacies must verify patient medication histories to avoid interactions.
For compounding pharmacies: Always document the patient’s medical history and concurrent medications to avoid adverse interactions.
Indocyanine Green vs. ICG Alternatives
How does ICG stack up against other diagnostic or surgical dyes? Let’s compare:
1. Indocyanine Green vs. Fluorescein Sodium
Fluorescein is used in ophthalmology (fluorescein angiography), but has limitations:
- Wavelength: Excited by blue light (490 nm), which is scattered by tissues, limiting the depth of imaging.
- Side Effects: More frequent allergic reactions (e.g., anaphylaxis).
ICG’s NIR fluorescence penetrates deeper, making it superior for choroidal and tumor imaging.
2. Indocyanine Green vs. Methylene Blue
Methylene blue is used for lymph node mapping, but it has risks:
- Toxicity: Can cause skin necrosis or serotonin syndrome (high doses).
- Imaging: Poor NIR fluorescence compared to ICG.
ICG is safer and provides better visualization of lymph nodes and tumors.
3. Indocyanine Green vs. Contrast Agents (e.g., Gadolinium)
Gadolinium-based agents are used in MRI but carry risks like nephrogenic systemic fibrosis (NSF) in patients with kidney disease. ICG:
- No known NSF risk.
- Rapid clearance reduces background noise in imaging.
For API importers: ICG’s advantages position it as a preferred choice for next-gen diagnostic tools, driving demand for high-purity APIs.
Is Indocyanine Green Safe During Pregnancy?
Pregnancy is a critical concern for compounding pharmacies and patients. Here’s what we know:
Limited Human Data:
ICG has not been adequately studied in pregnant women. Animal studies have shown no evidence of teratogenicity (congenital disabilities) at therapeutic doses; however, human data are sparse.
Clinical Use:
In urgent cases (e.g., life-threatening bleeding requiring ICG-guided surgery), the benefits may outweigh risks. However:
- Avoid routine use in pregnancy.
- Monitor fetal heart rate and maternal vital signs during administration.
Lactation:
ICG is excreted in breast milk in small amounts, but the risk to infants is unknown. Mothers should pump and discard milk for 24 hours post-administration.
For compounding pharmacies: Always consult with the prescribing physician and document the discussion in the patient’s record.
How Long Does Indocyanine Green Take to Work?
The onset of action depends on the route of administration and clinical application:
1. Ophthalmic Imaging
- Onset: 1–2 minutes after IV injection.
- Peak Effect: 5–10 minutes (optimal imaging window).
2. Oncologic Surgery
- Onset: 10–20 minutes after IV injection (time for tumor accumulation).
- Duration: Fluorescence persists for 1–2 hours (sufficient for most surgeries).
3. Liver Function Testing
- Onset: 5–10 minutes after IV injection.
- Peak Effect: 15–20 minutes (blood samples collected at this time).
Key Takeaway:
ICG acts quickly, but timing is critical for optimal results.
Compounding pharmacies must ensure that formulations are promptly reconstituted and administered to maintain potency.
Storage and Handling of Indocyanine Green
Unreconstituted ICG Bulk Powder: Store at 15-30°C in airtight, light-resistant containers.
Reconstituted Solution: Use within 6 hours; discard unused portions.
Compounding pharmacies should prioritize cold chain logistics and provide stability data for custom formulations (e.g., ICG-loaded nanoparticles).
API Sourcing and Quality Control for Indocyanine Green API
For API importers, sourcing high-quality ICG is non-negotiable.
Here’s what to look for:
1. Purity Standards
- Pharmaceutical Grade (USP/EP/JP): Required for medical use. Look for certificates of analysis (CoAs) verifying purity (>95% for most APIs).
- Industrial Grade: Lower purity (70–90%) for non-medical applications (e.g., textiles).
2. Regulatory Compliance
- GMP Approval: Ensure the supplier adheres to Good Manufacturing Practices (GMP) for Active Pharmaceutical Ingredients (APIs).
- Traceability: Verify batch numbers, production dates, and storage conditions (ICG degrades in light and moisture).
3. Supplier Reputation
- Experience: Choose suppliers with a proven track record in pharmaceutical APIs.
- Customer Support: Look for providers that offer technical assistance (e.g., formulation guidance and stability testing).
Pro Tip: Partner with suppliers that offer small-batch samples for testing before committing to large orders.
Compounding Pharmacy Considerations: Formulation and Storage
Compounding pharmacies face unique challenges when working with ICG. Here’s how to optimize your processes:
1. Formulation Guidelines
- Vehicle Selection: Use sterile water for injection (SWFI) or saline for IV formulations. For topical use, consider oil-in-water emulsions to enhance skin penetration and absorption.
- Stabilizers: Add antioxidants (e.g., sodium bisulfite) to prevent oxidation, which degrades ICG.
2. Storage
- Light Sensitivity: Store reconstituted solutions in amber vials or wrap them in aluminum foil to protect from light.
- Temperature: Keep at 2–8°C (refrigerated) for long-term storage; avoid freezing (may cause precipitation).
3. Patient Education
- Administration Timing: Instruct patients to use ICG-based products immediately after preparation.
- Adverse Reaction Reporting: Provide clear instructions on how to report side effects (e.g., itching, swelling).
Where to Source High-Quality Indocyanine Green API?
Not all ICG API suppliers are created equal.
When sourcing, prioritize:
- Certifications: Look for suppliers certified to ISO 9001, GMP, and FDA standards.
- Purity: Verify CoAs for impurity profiles (e.g., heavy metals, residual solvents).
- Lead Times: Ensure the supplier can meet bulk order demands without compromising quality.
Final Tip: Build relationships with suppliers that offer technical support—this can save time and reduce formulation errors.
Conclusion: Partnering for Precision in ICG Supply
For API importers and compounding pharmacies, ICG represents a growing market driven by advancements in surgery and the rise of personalized medicine.
Businesses can meet clinician demand by prioritizing regulatory compliance, adhering to sterile handling practices, and fostering effective supplier partnerships, while also prioritizing patient safety.
Stay ahead by investing in ICG’s emerging applications and educating healthcare providers on their benefits.
Do you need reliable ICG API suppliers or custom compounding support?
Contact us for cGMP-compliant ICG API and end-to-end regulatory guidance to drive revenue growth for your business.
Disclaimer:
This blog post is for informational purposes and does not constitute medical advice.
Always consult a healthcare professional before starting any new medication or treatment.
