Povidone iodine Other names: Iodopovidone

Povidone iodine is an iodophore that has an established use as a broad-spectrum antiseptic, mainly for the treatment of contaminated wounds and for the preoperative preparation of the skin, mucous membranes and the ocular surface. The organic complex contains approximately 10% of active available iodine.

Its spectrum of activity is iodine which gradually and slowly released exerts:

• bactericidal effect in less than 5 minutes in vitro, for all bacteria,
• fungicide effect for yeasts and filamentous fungi.

Solutions of povidone iodine gradually release iodine to exert an antimicrobial effect against bacteria, fungi, viruses, and spores. Although povidone iodine is less potent than preparations containing free iodine, it is also less toxic.

Organic materials (proteins, serum and blood) reduce the activity of free iodine, the active form of the medicinal product. Iodophores are unstable at alkaline pH.

Povidone iodine is a complex of the polymer polyvinylpyrrolidone (povidone) with iodine which, after application, continues to deliver iodine to the ocular surface over the short time that the solution is in contact with the eye.

After application, exposure of the ocular surface to iodine arises from the presence of free iodine in solution, and iodine bound to the polymer, which serves as a reservoir. As the preparation comes in contact with the eye, more and more iodine dissociates from the polymer.

Mechanisms of resistance

There are no reports of bacterial cross-resistance to antibiotics arising from exposure to povidone iodine, or iodine, or of co-resistance due to any known genetic linkage of resistance determinants.

There are limited reports of contamination of iodophores with Pseudomonas species, in nutrient restricted environments, such as hospital waste water, indicating that resistance to povidone-iodine can occur. However, this is of limited relevance to the use of povidone iodine in ocular antisepsis.

Povidone iodine administered clinically via any route can result in systemic absorption of iodine. The amount of absorbed iodine will vary according to the concentration of the povidone iodine preparation used, the number of applications and the route of administration.

Whilst absorption of iodine may occur following topical administration of all povidone iodine preparations, the effects are dose related. In view of the fact that a 10 second burst will deliver only 7mg of available iodine, the levels of iodine likely to be absorbed following topical administration will be exceedingly small and the effects on the internal organs minimal.

Any increase in the blood iodine level is generally transient. In patients with a healthy thyroid, the increased iodine level does not lead to any clinically relevant changes in thyroid hormone status. When iodine metabolism is normal, increased amounts of iodine are excreted via the kidneys.

The available iodine in iodinated povidone is able to cross the conjunctival barrier to a limited extent. At the concentration used, the potential for systemic exposure to iodine is very low.

Conjunctival and peri-ocular sterilisation with iodinated povidone (1.25% or 10%) results in increased urinary elimination of iodide. Elimination is almost exclusively by the renal route. Povidone alone is unlikely to be absorbed systemically.

Preclinical data from safety pharmacology studies, repeated dose toxicity tests and mutagenicity studies did not provide evidence of a particular risk to humans. Animal studies did not show any teratogenic effects.

In oral sub-acute and chronic toxicity studies, including rat studies, the only effects observed after discontinuation of povidone iodine were in most cases transient and dose-dependent increases in serum iodine-bound protein and non-specific histopathological changes in the thyroid gland.