Lugol's iodine

Lugol's iodine

2% Lugol's iodine solution
Clinical data
Other names	Potassium triiodide, Lugol's solution, aqueous iodine, strong iodine solution[1]
AHFS/Drugs.com	Monograph
License data	US DailyMed: Lugols_solution
Routes of administration	topical, by mouth
Identifiers
CAS Number	12298-68-9
DrugBank	DB14492
UNII	T66M6Y3KSA
CompTox Dashboard (EPA)	DTXSID1047154
Chemical and physical data
Formula	I3K
Molar mass	419.812

Lugol's iodine, also known as aqueous iodine and strong iodine solution, is a solution of

• 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.^[14] With Lugol’s iodine, low-grade dysplasia appears as an unstained or weakly stained area; high-grade dysplasia is consistently unstained.^[15]
• Lugol's iodine may also be used to better visualize the
  keratinized gingiva.^[16]
• 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.^[17]

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
  organic compounds,^[18] 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.

Outdated uses

• Till early 1970s, it was often recommended for use in victims of rape in order to avoid pregnancy. The idea stemmed from the fact that, in the laboratory, Lugol's iodine appeared to kill sperm cells even in such great dilutions as 1:32. Thus it was thought that an intrauterine application of Lugol's iodine, immediately after the event, would help avoid pregnancy.^[19]

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 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).[22] The Global Harmonized System of Classification and Labeling of Chemicals categorizes this as Category 2 with a hazard statement "Fatal if swallowed".^[23] Potassium iodide is not considered hazardous.^[24]

Mechanism of action

The above uses and effects are consequences of the fact that the solution is a source of effectively free elemental iodine, which is readily generated from the equilibrium between elemental iodine molecules and polyiodide ions in the solution.

History

It was historically used as a first-line treatment for hyperthyroidism, as the administration of pharmacologic amounts of iodine leads to temporary inhibition of iodine organification in the thyroid gland, caused by phenomena including the Wolff–Chaikoff effect and the Plummer effect. However it is not used to treat certain autoimmune causes of thyroid disease as iodine-induced blockade of iodine organification may result in hypothyroidism. They are not considered as a first line therapy because of possible induction of resistant hyperthyroidism but may be considered as an adjuvant therapy when used together with other hyperthyroidism medications.

Lugol's iodine has been used traditionally to replenish iodine deficiency. Because of its wide availability as a drinking-water decontaminant, and high content of potassium iodide, emergency use of it was at first recommended to the Polish government in 1986, after the

Historically, Lugol's iodine solution has been widely available and used for a number of health problems with some precautions.[28] Lugol's is sometimes prescribed in a variety of alternative medical treatments.^[29][30] Only since the end of the Cold War has the compound become subject to national regulation in the English-speaking world.^{[citation needed]}

Society and culture

Regulation

Until 2007, in the United States, Lugol's solution was unregulated and available over the counter as a general reagent, an antiseptic, a preservative,^[31] or as a medicament for human or veterinary application.

Since 1 August 2007, the

Lugol's solution is commonly available in different potencies of (nominal) 1%, 2%, 5% or 10%. Iodine concentrations greater than 2.2% are subject to US regulations.[11]^[33][34] If the US regulations are taken literally, their 2.2% maximum iodine concentration limits a Lugol's solution to maximum (nominal) 0.87%.

The most commonly used (nominal) 5% solution consists of 5% (

In the United Kingdom, in 2015, the NHS paid £9.57 per 500 ml of solution.[4]

References