A study observing the reactions that occur when commonly used surgical antiseptics are mixed found that at least two of the reactions tested—chlorhexidine + Dakin’s solution (sodium hypochlorite) and Dakin’s solution + hydrogen peroxide—yielded byproducts that are potentially toxic to human beings. The findings were presented in Scientific Poster 696 at the AAOS 2018 Annual Meeting.

The investigators mixed all combinations of four antiseptic solutions commonly used in total joint arthroplasty: 4 percent chlorhexidine gluconate (CHX); Dakin’s solution (0.5 percent sodium hypochlorite, or NaOCl); povidone-iodine (betadine, or BTD); and hydrogen peroxide (H₂O₂). These agents are among those that may be used for irrigation and lavage in the process of addressing acute infection with arthrotomy, excision of infected tissue, and exchange of modular components while well-fixed implants are retained.

Sean T. Campbell, MD, lead author of the study, explained that the literature provides little guidance on which of these antiseptic solutions is most effective. Some authors have discussed the combined use of the agents, but no work to date has determined how frequently this mixed usage is practiced. He and his colleagues were prompted to undertake the study after the senior author, Nicholas J. Giori, MD, PhD, happened to notice during a débridement procedure that two solutions—chlorhexidine gluconate and Dakin’s solution—were inadvertently combined on a back table in the operating room and reacted to form a precipitate.

“We hadn’t seen this reaction described elsewhere in the arthroplasty or orthopaedic literature, and thought it would be interesting and informative to characterize this reaction,” Dr. Campbell explained. “This led us down the path to looking at various other reactions and their interactions as well.”

For the study, all possible combinations of 4 percent CHX, 0.5 percent NaOCl, 3 percent H2O2, and 10 percent betadine solutions were mixed in clean test tubes. The researchers first added 2.5 cc of one reagent, followed by 2.5 cc of the second. The solutions were observed immediately and after agitation. Because the reactions were previously undefined and the exact stoichiometry required to yield products (if any) was unknown, an additional 2.5 cc of the original reagent was added to the mixture if no reaction occurred initially. Results were recorded and photographs were taken.

Among the mixtures, CHX and NaOCl, CHX and hydrogen peroxide, and CHX and betadine reacted instantly and formed a precipitate. NaOCl and hydrogen peroxide reacted to produce a gas but no precipitate. NaOCl and betadine did not react initially, but when the additional NaOCl was added, a reaction (color change) was observed. Only hydrogen peroxide and betadine did not react in a visible manner.

The combination of Dakin’s solution with two of the other agents—chlorhexidine and hydrogen peroxide—formed products with the potential for toxicity. The reaction of NaOCl and CHX has been described in the literature as producing parachloroaniline, which is flammable and which in high concentrations has been shown to be carcinogenic in rats and methemoglobinemia-inducing in humans. The mixture of NaOCl and hydrogen peroxide yields water, chlorine ion, and oxygen. Some of this oxygen is singlet oxygen, which is known to be highly reactive. Singlet oxygen is bactericidal but also has been shown to penetrate eukaryotic cells, cause cellular injury, and alter expression of messenger RNA.

The combination of CHX and hydrogen peroxide has been shown to be more effective than CHX alone for disinfection, and no literature discusses possible products formed in the reaction between these two antiseptics. The combination of CHX and betadine has a similar profile in this context, with no studies describing potential hazards. NaOCl with betadine involves a well-characterized multi-step reduction-oxidation reaction between the iodine ion and hypochlorite of unknown clinical significance if occurring in vitro.

Of the results, Dr. Campbell said, “What was surprising was how many of the solutions reacted chemically when combined.”

Limitations of the study, he said, “include the fact that we did not objectively quantify the products formed during the reactions we noticed. We also did not confirm the product identities with analytic testing.”

Other areas of study that could be considered, he suggested, would be other commonly used antiseptic solutions, such as castile soap, bacitracin, and acetic acid.

Dr. Campbell said the takeaway from the study “is that surgeons should think carefully when considering using multiple antiseptics to irrigate a wound. We recommend avoiding potentially toxic antiseptic combinations
altogether.”

Dr. Campbell’s and Dr. Giori’s co-authors of Poster 696, “Antiseptics Commonly Used in Total Joint Arthroplasty Interact and May Form Toxic Products,” are Lawrence H. Goodnough, MD, PhD; and Chase G. Bennett, MD.

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.now.