Lugol's iodine, also known as aqueous iodine and strong iodine solution, is a solution of potassium iodide with iodine in water. It is a medication and disinfectant used for a number of purposes. Taken by mouth it is used to treat thyrotoxicosis until surgery can be carried out, protect the thyroid gland from radioactive iodine, and to treat iodine deficiency. When applied to the cervix it is used to help in screening for cervical cancer. As a disinfectant it may be applied to small wounds such as a needle stick injury. A small amount may also be used for emergency disinfection of drinking water. Side effects may include allergic reactions, headache, vomiting, and conjunctivitis. Long term use may result in trouble sleeping and depression. It should not typically be used during pregnancy or breastfeeding. Lugol's iodine is a liquid made up of two parts potassium iodide for every one part elemental iodine in water. Lugol's iodine was first made in 1829 by the French physician Jean Lugol. It is on the World Health Organization's List of Essential Medicines. Lugol's iodine is available as a generic medication and over the counter. Lugol's solution is available in different strengths of iodine. Large volumes of concentrations more than 2.2% may be subject to regulation.
Uses
Medical uses Preoperative administration of Lugol's solution decreases intraoperative blood loss during thyroidectomy in patients with Graves' disease. However, it appears ineffective in patients who are already euthyroid on anti-thyroid drugs and levothyroxine.
During colposcopy, Lugol's iodine is applied to the vagina and cervix. Normal vaginal tissue stains brown due to its high glycogen content, while tissue suspicious for cancer does not stain, and thus appears pale compared to the surrounding tissue. Biopsy of suspicious tissue can then be performed. This is called a Schiller's test. Patients at high risk of oesophageal squamous cell carcinoma are usually followed using a combination of Lugol's chromoendoscopy and narrow-band imaging. With Lugol's iodine, low-grade dysplasia appears as an unstained or weakly stained area; high-grade dysplasia is consistently unstained. Lugol's iodine may also be used to better visualize the mucogingival junction in the mouth. Similar to the method of staining mentioned above regarding a colposcopy, alveolar mucosa has a high glycogen content that gives a positive iodine reaction vs. the keratinized gingiva. Lugol's iodine may also be used as an oxidizing germicide, however it is somewhat undesirable in that it may lead to scarring and discolors the skin temporarily. One way to avoid this problem is by using a solution of 70% ethanol to wash off the iodine later. Lugol's iodine was distributed in Polish People's Republic after the Chernobyl catastrophe, due to government not being informed of how severe the event was and overestimating radiation, and unavailability of iodine tablets.
Science As a mordant when performing a Gram stain. It is applied for 1 minute after staining with crystal violet, but before ethanol to ensure that gram positive organisms' peptidoglycan remains stained, easily identifying it as a gram positive in microscopy. This solution is used as an indicator test for the presence of starches in organic compounds, with which it reacts by turning a dark-blue/black. Elemental iodine solutions like Lugol's will stain starches due to iodine's interaction with the coil structure of the polysaccharide. Starches include the plant starches amylose and amylopectin and glycogen in animal cells. Lugol's solution will not detect simple sugars such as glucose or fructose. In the pathologic condition amyloidosis, amyloid deposits (i.e., deposits that stain like starch, but are not) can be so abundant that affected organs will also stain grossly positive for the Lugol reaction for starch. It can be used as a cell stain, making the cell nuclei more visible and for preserving phytoplankton samples. Lugol's solution can also be used in various experiments to observe how a cell membrane uses osmosis and diffusion. Lugol's solution is also used in the marine aquarium industry. Lugol's solution provides a strong source of free iodine and iodide to reef inhabitants and macroalgae. Although the solution is thought to be effective when used with stony corals, systems containing xenia and soft corals are assumed to be particularly benefited by the use of Lugol's solution. Used as a dip for stony and soft or leather corals, Lugol's may help rid the animals of unwanted parasites and harmful bacteria. The solution is thought to foster improved coloration and possibly prevent bleaching of corals due to changes in light intensity, and to enhance coral polyp expansion. The blue colors of Acropora spp. are thought to be intensified by the use of potassium iodide. Specially packaged supplements of the product intended for aquarium use can be purchased at specialty stores and online. This and other iodide-iodine solutions can also function as a less toxic replacement for aqua regia, allowing for gold to be dissolved without the use of strong acids.
Side effects Because it contains free iodine, Lugol's solution at 2% or 5% concentration without dilution is irritating and destructive to mucosa, such as the lining of the esophagus and stomach. Doses of 10 mL of undiluted 5% solution have been reported to cause gastric lesions when used in endoscopy. The LD50 for 5% Iodine is 14,000 mg/kg (14 g/kg) in rats, and 22,000 mg/kg (22 g/kg) in mice. The World Health Organization classifies substances taken orally with an LD50 of 5–50 mg/kg as the second highest toxicity class, Class Ib (Highly Hazardous). The Global Harmonized System of Classification and Labeling of Chemicals categorizes this as Category 2 with a hazard statement "Fatal if swallowed". Potassium iodide is not considered hazardous.
Mechanism of action Potassium iodide is a common additive used for iodizing, which helps preserve and solublize the iodine component of Lugol's iodine. The iodine component of this solution is used as an antiseptic, but is poorly water-soluble iodine without the addition of potassium iodide.
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