The brown surgical antiseptic works by rationing its iodine very slowly
Plain iodine kills germs well but stings, stains and poisons tissue. In 1955 two Philadelphia researchers bound it to a polymer called povidone, so only a trickle of free iodine escapes at a time. The result, sold as Betadine among other brands, is now on the WHO's List of Essential Medicines.
Iodine was discovered by Bernard Courtois in 1811 and soon became a standard wound treatment, effective against bacteria, fungi, viruses and protozoa. Its drawbacks in water solutions were irritation, toxicity and stained skin. H. A. Shelanski and M. V. Shelanski of the Industrial Toxicology Laboratories solved much of this by mixing iodine with the polymer polyvinylpyrrolidone. In mice their complex proved less toxic than tincture of iodine, and human trials rated it better than rival iodine preparations. It went on sale that same year.
The trick is controlled release. Free iodine seeps gradually from the complex and kills microbes by iodinating fats and oxidising compounds inside cells and their membranes, while the low concentration spares human cells. Because soft tissue absorbs it slowly, its effect outlasts iodine tincture, which is why surgeons have favoured it for long operations. It dissolves in water and several alcohols and is far more stable in solution than Lugol's solution.
Uses range widely: hand and skin preparation before surgery, minor cuts and burns, chronic ulcers, and a buffered 2.5 percent eye solution to guard newborns against conjunctivitis, though whether it beats alternatives there is unclear. Doctors also use it to fuse the lining of the lungs in stubborn fluid build-ups, where it matches talc and costs less. The recommended 10 percent strength is unpopular with staff because it dries so slowly.
Comparisons are not all flattering. Strong evidence favours chlorhexidine with alcohol for skin cleansing, and the WHO backed that option in 2016, yet a 2024 trial of over 3,300 heart and abdominal surgery patients found alcohol-based povidone-iodine was no worse at preventing wound infections. Non-sterile stock has a history of contamination with Burkholderia cepacia, a bacterium that resists it, so claims that germs never become resistant deserve caution. It is contraindicated in some thyroid conditions, reacts with metals and hydrogen peroxide, and can skew thyroid tests.
Source: Povidone-iodine
