Halogens - Disinfectants, Antiseptics, & Sterilants

HALOGENS

Iodine

Iodine in a 1:20,000 solution is bactericidal in 1 minute and kills spores in 15 minutes. Tincture of iodine USP contains 2% iodine and 2.4% sodium iodide in alcohol. It is the most active antiseptic for intact skin. It is not commonly used because of serious hyper-sensitivity reactions that may occur and because of its staining of clothing and dressings.

Iodophors

Iodophors are complexes of iodine with a surface-active agent such as polyvinyl pyrrolidone (PVP; povidone-iodine). Iodophors retain the activity of iodine. They kill vegetative bacteria, myco-bacteria, fungi, and lipid-containing viruses. They may be spori-cidal upon prolonged exposure. Iodophors can be used as antiseptics or disinfectants, the latter containing more iodine. The amount of free iodine is low, but it is released as the solution is diluted. An iodophor solution must be diluted according to the manufacturer’s directions to obtain full activity.

Iodophors are less irritating and less likely to produce skin hypersensitivity than tincture of iodine. They require drying time on skin before becoming active, which can be a disadvantage. Although iodophors have a somewhat broader spectrum of activ-ity than chlorhexidine, including sporicidal action, they lack its persistent activity on skin.

Chlorine

Chlorine is a strong oxidizing agent and universal disinfectant that is most commonly provided as a 5.25% sodium hypochlorite solution, a typical formulation for household bleach. Because formulations may vary, the exact concentration should be verified on the label. A 1:10 dilution of household bleach provides 5000 ppm of available chlorine. The CDC recommends this concentration for disinfection of blood spills. Less than 5 ppm kills vegetative bac-teria, whereas up to 5000 ppm is necessary to kill spores. A con-centration of 1000–10,000 ppm is tuberculocidal. One hundred ppm kills vegetative fungal cells in 1 hour, but fungal spores require 500 ppm. Viruses are inactivated by 200–500 ppm. Dilutions of 5.25% sodium hypochlorite made up in pH 7.5–8.0 tap water retain their activity for months when kept in tightly closed, opaque containers. Frequent opening and closing of the container reduces the activity markedly.

Because chlorine is inactivated by blood, serum, feces, and protein-containing materials, surfaces should be cleaned before chlorine disinfectant is applied. Undissociated hypochlorous acid (HOCl) is the active biocidal agent. When pH is increased, the less active hypochlorite ion, OCl^–, is formed. When hypochlorite solutions contact formaldehyde, the carcinogen bischloromethyl is formed. Rapid evolution of irritating chlorine gas occurs when hypochlorite solutions are mixed with acid and urine. Solutions are corrosive to aluminum, silver, and stainless steel.

Alternative chlorine-releasing compounds include chlorinedioxide and chloramine T. These agents retain chlorine longerand have a prolonged bactericidal action.