SAN ANTONIO, Texas — Hypochlorous acid causes less pain than povidone iodine when used as a disinfectant prior to intravitreal injections, researchers say.

Povidone iodine is the standard of care, but hypochlorous acid could offer a viable alternative, at least in patients who find povidone iodine unbearable, said Robert L. Avery, MD, of California Retina Consultants in Santa Barbara, California, who presented the finding at the American Society of Retina Specialists (ASRS) 2021 annual meeting.

“There is no question it’s less painful,” he told Medscape Medical News. “The only question is whether it does the job as well.”

To compare the two treatments, Avery and his colleagues recruited 62 patients and treated one eye in each patient with hypochlorous acid and the other eye with povidone iodine.

After instilling the disinfectant, the researchers asked the patients to rate their pain on a scale from 1 to 10, with 10 the worst pain the patients had ever felt. The researchers repeated the question immediately after the injection, and 1-2 hours after the injection.

Table. Disinfectant Pain
Disinfectant	After Disinfectant, 1-10 scale	Immediately After Injection, 1-10 scale	1-2 Hours After Injection, 1-10 scale
Povidone Iodine	1.15	1.02	3.00
Hypochlorous Acid	0.11	0.78	0.47
P value	< .001	.19	< .001

An hour or two after the procedure, 51 of the patients said that the eye treated with hypochlorous acid was more comfortable than the eye treated with povidone iodine. None said the eye treated with povidone iodine felt better, while eight said there was no difference and three didn’t respond. Thirty-nine reported a foreign-body sensation in their eye with povidone iodine, vs three who said the same about their eye with hypochlorous acid.

The proportion of negative cultures was 68% with povidone iodine and 47% with hypochlorous acid. The difference was not statistically significant (P = .067), and none of the patients got endophthalmitis, but the trend toward more negative cultures with povidone iodine raises concerns about hypochlorous acid, said Avery.

Previous studies have shown better disinfectant results with increased application of povidone iodine drops; the same might be true of hypochlorous acid, said Avery. When using it in his own practice for patients who can’t tolerate povidone iodine, Avery applies hypochlorous acid up to five times before and after applications of an anesthetic gel.

A randomized controlled trial is underway to provide a more definitive comparison of the two disinfectants, Avery said.

Hypochlorous acid is an important potential addition to the armamentarium for infection control in intravitreal injections, said Linda Lam, MD, MBA, a professor of ophthalmology at the University of Southern California Roski Eye Institute in Arcadia. “It’s the aspect of the procedure that patients are most unhappy about,” she told Medscape Medical News .

Like Avery, she would need to see more research before using hypochlorous acid routinely. But she said it could be useful in those patients who are unwilling to be treated again after they have experienced the sting of povidone iodine. “There are many patients who just don’t come back,” she said.

The study was funded by California Retina Research Foundation. Avery reported consulting for companies that make drugs for intravitreal injection. Lam has disclosed no relevant financial relationships.

American Society of Retina Specialists: Comparison of Hypochlorous Acid vs Povidone Iodine Use Prior to Intravitreal Injection: A Randomized Prospective Trial (PAVE Study). Presented October 9, 2021.

Laird Harrison writes about science, health, and culture. His work has appeared in national magazines, in newspapers, on public radio, and on websites. He is at work on a novel about alternate realities in physics. Harrison teaches writing at the Writers Grotto. Visit him at lairdharrison.com or follow him on Twitter: @LairdH.

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