Iodine is a necessary element for life, thus an allergy to elemental iodine is not possible. Nevertheless, iodine containing chemicals can provoke 3 types of reactions on human contact: an irritant contact dermatitis, an allergic contact dermatitis, and a generalized anaphylaxis.
First, an irritant reaction to iodine is an effect of the body's innate immune system and, as such, a skin response can be provoked immediately without prior exposure. Compared with tinctures of pure iodine, these types of reactions are less frequent with the lower levels of free iodine encountered with iodophores, but they are still common and depend on the exposure time and concentration. As opposed to an irritant reaction, an allergic reaction to the iodophore is mediated by T lymphocytes.
In a review published in The Journal of Vitreoretinal Diseases ,authors have discussed the role of povidone-iodine (PI) for endophthalmitis prophylaxis in ophthalmic procedures, stating that it is an essential component, that true PI allergy is rare, and that reported allergy to iodine, shellfish, or contrast media is not a contraindication.
It is now well documented that the antiseptic povidone iodine (PI) is a key component of endophthalmitis prophylaxis. Due to wide evidence of data showing that PI effectively reduces bacterial counts in 30 seconds and that the fastest in vitro killing time is achieved with 0.1% PI rather than more-concentrated formulations, The American Academy of Ophthalmology recommends using 5% PI,25 and recent in vivo studies have shown that 5% PI is as effective as 10% in the setting of IVIs.
"Despite its availability, 34 years passed before the significant utility of PI was demonstrated in a clinical trial of cataract surgery. it is now standard practice not only in the operating room but also in intravitreal injection (IVI) protocols.6-8 Key aspects of PI include short application time for effectiveness,9 efficacy of dilute concentrations,10 lack of microbial resistance,11,12 ability to penetrate biofilm,13 and safety to the retina." wrote the reviewers.
According to the team, a recent retrospective review emphasized the increased rate of endophthalmitis in IVIs without PI and the much lower risk when it is used. This study reported that 11.9% of post-IV endophthalmitis cases occurred when PI was omitted from the preparation. Furthermore, injections lacking PI antisepsis had an estimated infection rate of 9.4%, whereas the study's overall incidence of endophthalmitis after injection was 0.019%. These findings emphasize that, despite its critical, widely accepted role in endophthalmitis prevention, a clinical dilemma arises when patients endorse an "allergy" that may contraindicate PI application.
The reviewers further stated that though present guidelines note that true allergy to PI is rare and anaphylaxis after ophthalmic use has never been described, physicians still hesitate to use the antiseptic in these situations. Although patients may have true allergies to these other substances, no data suggest that using topical PI for endophthalmitis prophylaxis in these patients is contraindicated.
"PI is an essential component of reducing the risk of endophthalmitis after ophthalmic procedures. As such, clinical scenarios that justify withholding PI are rare. Given the infrequency of a true allergy to PI, physicians should critically consider any reported reactions to the antiseptic itself."concluded the reviewers.
Primary source: Journal of Vitreoretinal Diseases
For full article click on the link: "Iodine Allergy" and the Use of Povidone Iodine for Endophthalmitis Prophylaxis
J Vitreoretin Dis 2019 Oct 14;4(1)65, JW Hinkle, CC Wykoff, JI Lim, P Hahn, SJ Kim, H Tabandeh, HW Flynn Jr