1. Clinical Overview
Fluorescein sodium is a diagnostic dye used primarily in ophthalmology. The 20% concentration is a sterile, injectable solution for intravenous administration. It is a fluorescent compound that, when excited by blue light (wavelength 465-490 nm), emits a yellow-green fluorescence (520-530 nm). This property allows for the visualization of blood flow and the detection of vascular abnormalities in the retina and choroid, as well as corneal epithelial defects. It is a cornerstone of diagnostic retinal imaging.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 10-15 seconds after intravenous injection. | The initial vascular filling phase lasts 30-60 seconds. Fluorescence in tissues can persist for several hours, but the diagnostic window for angiography is typically 10-15 minutes. | 100% (Intravenous administration). |
2. Mechanism of Action
Fluorescein sodium is a small, water-soluble molecule that diffuses freely through most capillaries but not through the tight junctions of the retinal vascular endothelium (blood-retinal barrier). When injected intravenously, it circulates with the blood. Under blue excitation light, it emits yellow-green fluorescence, allowing real-time visualization of the retinal and choroidal circulation. Leakage, pooling, or staining patterns indicate breakdown of vascular integrity or barriers.
3. Indications & Uses
- Diagnostic Fluorescein Angiography (FA/FFA) of the retina and choroid
- Evaluation of retinal and choroidal circulation
- Detection of macular edema
- Diagnosis and management of diabetic retinopathy
- Evaluation of retinal vascular occlusions (BRVO, CRVO)
- Assessment of age-related macular degeneration (AMD) - both dry and wet forms
- Diagnosis of retinal neovascularization
4. Dosage & Administration
Adult Dosage: 500 mg (2.5 mL of 20% solution) administered as a rapid intravenous bolus injection into a large antecubital vein. Typical dose range is 500-750 mg (2.5-3.75 mL).
Administration: 1. Use a sterile 3-5 mL syringe with a 20-23 gauge needle. 2. Ensure IV access is secure to prevent extravasation. 3. Inject rapidly as a bolus (over 2-5 seconds) followed by a saline flush. 4. Angiography imaging sequences begin immediately after injection. 5. Patient should be in a seated or reclined position for the procedure. 6. Resuscitation equipment (adrenaline, antihistamines, oxygen) must be immediately available.
5. Side Effects
Common side effects may include:
- Nausea (5-10%)
- Vomiting (1-5%)
- Transient yellow discoloration of skin and conjunctiva (100%, lasts 6-12 hours)
- Bright yellow-orange discoloration of urine (100%, lasts 24-36 hours)
- Metallic or unusual taste in mouth
- Sneezing
- Pruritus (itching)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Probenecid | May competitively inhibit renal tubular secretion of fluorescein, potentially prolonging its half-life and increasing plasma levels. | Moderate |
| Other diagnostic dyes (e.g., Indocyanine Green - ICG) | If administered concurrently, may interfere with fluorescence imaging. Sequential administration with a waiting period is standard. | Moderate |
7. Patient Counselling
- DO inform your doctor about all allergies, especially previous reactions to dyes, iodine, or contrast media.
- DO inform your doctor if you are pregnant, planning pregnancy, or breastfeeding.
- DO inform about any kidney, liver, or heart problems.
- DO have a light meal 1-2 hours before the test to reduce nausea.
- DON'T be alarmed by yellow skin or bright orange urine; it is normal and will fade in 1-2 days.
- DON'T drive yourself home after the procedure; arrange for transportation.
8. Toxicology & Storage
Overdose: Symptoms would be an exaggeration of known adverse effects: severe nausea, vomiting, hypotension, shock, convulsions, and potentially cardiorespiratory collapse. The LD50 in humans is not established.
Storage: Store at room temperature (15-25°C). Protect from light. The solution is clear and orange-red. Do not use if the solution is cloudy, discolored, or contains particulate matter. Keep out of reach of children. Single-use vial; discard any unused portion.