Fluorescein is a dye used particularly as a fluorescent agent in diagnostic procedures at various levels.
As an ocular disclosing agent, fluorescein sodium dissolves readily in aqueous alkaline solutions, responds to 465 to 490 nm at cobalt blue light, and fluoresces at 520 to 530 nm as bright green. The compound contains a conjugated system that illuminates when electrons spend a prolonged time in an excited state.
When using fluorescein to stain cells, its charged ends attract to the hydrophilic ends in the cell membrane to form a strong electrostatic bond. One or more of the charged ends of fluorescein may then be modified for greater interaction.
Ophthalmic administration of fluorescein starts with a paper strip with one tip stained with fluorescein. The paper strip is moistened with saline water, then placed on the conjunctiva or inferior fornix. The patient may blink a few times to spread the dye across the eye.
Fluorescein solution may be administered orally and requires 10-15 minutes before appearing. Although the solution is bitter, combining it with sugar or a beverage can increase palatability.
Intravenous injection of fluorescein sodium occurs at the antecubital vein. The dye appears almost immediately in the retina and choroidal vessels (in 7 to 14 seconds). In the case of anaphylaxis, IV access is still necessary for epinephrine.
After administration, the examiner can extinguish the room light to view the fluorescence of the dye under cobalt blue light.
Common: paresthesia of lips, change in taste (orally), severe eye irritation (ophthalmic), severe nausea, vomiting, abdominal pain, chest pain, and extravasation.
Hypersensitivity to fluorescein formulation prevents its application. Furthermore, even though more research is needed to determine side effects on a fetus, pregnancy may be considered a relative contraindication. 
Fluorescein has no known significant drug interactions. Under ophthalmic examination, contact lens removal is necessary with the use of fluorescein to avoid unnecessary staining. Fluorescein completely clears through urine excretion 2 to 3 days after injection.
Fluorescein toxicity is low. Proper doses of epinephrine and antihistamines can manage cases of significant hypersensitivity after flushing the affected area with plenty of water. Prevention of anaphylaxis is possible by providing a minimal dose of fluorescein to determine if a minor reaction would occur.
If enough fluorescein is issued intravenously, then precaution must be taken for nursing mothers because another route of excretion is through human milk, causing it to turn yellow.
Because fluorescein administration is for diagnostic purposes, its use is most commonly by specialists, especially ophthalmologists and surgeons, but also general practitioners, where nurses and/or medical assistants may also assess proper dosage for the desired procedure. Not all health professionals readily operate with a fluorescent agent. [Level V]
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