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Citation: Jones V, Milton T (2000) When and how to use iodine dressings. Nursing Times; 96: 45, 2.

Authors Vanessa Jones is education director; Tanya Milton is research nurse; both at the Wound Healing Research Unit, University of Wales College of Medicine, Cardiff.

Iodine is an antiseptic that kills bacteria and pathogens (Lawrence, 1998). In the past its clinical use was limited by the fact that elemental iodine can cause irritation to the skin, be absorbed systemically and is almost insoluble in water.

Iodine can be used for wound cleansing and debridement (Sundberg and Meller, 1997), and for the prevention and treatment of infection (Skog, 1983). Recent research has generated interest in its ability to promote healing by influencing the production and activity of certain cells in the immune system (Moore et al, 1997).

The term iodine is sometimes used to denote all iodine formulations, when in fact there are two distinct preparations:

Each has different physical characteristics that relate to its component parts and the concentration of available iodine that is released when it is used (Gilchrist, 1997).

Povidone iodine is an iodophor composed of a water-soluble complex of elemental iodine and a synthetic polymer. This is referred to as polyvinylpyrrolidone iodine or PVP-I (Mayer and Tsapogas, 1993). 

PVP-I has an affinity to cell membranes and will deliver iodine directly to the surface of the cell. Its role as an antimicrobial agent is not clear (Zamora, 1986). Some researchers have reported a wide range of activity against gram-negative and gram-positive bacteria, fungi, viruses and protozoa. Others found that using differing concentrations of iodine in this form made little difference to wound pathogens (Mertz et al, 1984; Lammers et al, 1990).

Research has identified that iodine in different concentrations can affect fibroblasts, which have a pivotal role in wound healing. However, concerns about this toxic effect on wound healing originated not from clinical studies but from tests on animals (Geronemus et al, 1979; Brennan and Leaper, 1985: Kashyap et al, 1995) and in vitro work (Mayer, 1994; Moore, 1996).

The use of PVP-I as a topical preoperative skin disinfectant is well established. In patients with burns, topical povidone iodine provides effective antibacterial prophylaxis (Lawrence, 1992). The most commonly used dressing is an impregnated tulle.

Iodine can cause local adverse effects such as irritant skin reactions and allergic contact dermatitis (Tosti et al, 1990). It should be used with caution, and if possible avoided, in patients with disorders of the thyroid gland as its use can result in hyperthyroidism.

Similarly, patients with diabetes who are taking sulphonamides or sulphonylureas, which inhibit thyroid hormone synthesis, should be observed for possible toxic effects and it may be necessary to check their thyroid hormone levels.

Severe cutaneous reactions are rare, but nurses should always stop using iodine if they occur. There is no strong evidence that products that contain PVP-I pose any hazard to wound healing, but because of its broad antimicrobial properties it appears that it may play an important role in the prevention and treatment of wound infection (Mayer and Tsapogas, 1993).

Iodine is diluted and can soon be broken down if it comes into contact with exudate and proteins on the wound surface. This reduces any long-term effects it may have. The benefits of PVP-I generally last for a few hours, but subsequent dilution usually makes it necessary to change dressings at least once a day. PVP-I is therefore recommended for use on infected wounds with low levels of exudate and wounds that need frequent dressing changes.

Cadexomer iodine is a three-dimensional starch lattice formed into spherical microbeads containing 0.9% iodine. These beads are highly absorbent and the pores of the lattice increase in size when they are exposed to exudate, allowing the gradual release of iodine (Sundberg and Meller, 1997).

All three proprietary forms of cadexomer iodine are made up of the same formulation and are available as a powder, paste dressing or ointment (Thomas and Leigh, 1998).

The slow release of the iodine in these preparations allows the wound to remain in continuous contact with it, whereas with a single exposure to a product such as PVP-I tulle the iodine is soon broken down (Sundberg and Meller, 1997).

The beads also absorb debris and can therefore be used to remove it from the wound bed, making cadexomer iodine a useful debriding agent.

Ointments containing cadexomer iodine have been shown to be effective against a variety of organisms, such as Staphylococcus aureus, β-haemolytic streptococcus and pseudomonas, in a number of different types of wound.

In a study of 28 patients with venous leg ulcers, Steele et al (1986) found that it was effective in dirty, odorous ulcers and Apelqvist et al (1992) found it useful in controlling exudate in diabetic foot ulcers. Cadexomer iodine has also proven effective against methicillin-resistance S. aureus in pig wounds (Mertz et al, 1994) and experimental wounds (McLure and Gordon, 1992).

The most common adverse effect is a burning or stinging sensation on application, local irritation, redness and eczema (Holloway et al, 1989). Safety studies have demonstrated that cadexomer iodine poses minimal risk to thyroid function (Skog et al, 1983).

Cadexomer iodine is useful when treating infected wounds with moderate amounts of exudate and sloughy wounds. Its ability to release iodine slowly means that it is recommended for use on chronic wounds where less frequent dressing changes are required.

A number of published clinical trials on the use of PVP-I and cadexomer iodine support the use of iodine products, but much of this research has been carried out in laboratories or on animals and all of the studies involved use a wide variety of different preparations.

However, it appears that the latest, low-concentration, slow-release iodine formulations that are now in use in clinical practice are effective and non-toxic. Previous concerns about iodine were based on the toxicity of older formulations that contained elemental iodine.

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