FDA approval awaited for latex allergy reagent
FDA approval awaited for latex allergy reagent
Skin test would identify latex-allergic HCWs
When a new non-ammoniated latex skin test reagent currently under development receives federal approval, it will go a long way toward solving the problem of definitively diagnosing latex allergies in health care workers, as well as in other high-risk populations.
Presently, occupational health practitioners detect latex allergies in HCWs by their responses to questionnaires (see Hospital Employee Health, January 1997, p. 6; December 1997, pp. 149-150), through suggestive clinical histories, and from screening exams. Some workers then are referred to allergists for serological testing, which often requires several days' wait for results. A reliable skin test, which allergists generally prefer, has not been available in the United States.
But Hospital Employee Health has learned that one such test has been developed and awaits U.S. Food and Drug Administration (FDA) approval. Robert G. Hamilton, PhD, associate professor of medicine at Johns Hopkins University School of Medicine in Baltimore, is leading research efforts in developing a reliable puncture skin test that allergists can use to diagnose latex allergy in HCWs, as well as in children with spina bifida, another high-risk population.
Hamilton has conducted clinical trials of the reagent on HCWs at 12 U.S. health centers. Of the 304 adults tested, 124 were latex-allergic and 180 were not. All provided blood samples and then received sequential puncture skin tests (PSTs) using the reagent. A two-stage glove provocation test was used to clarify latex allergy status of individuals with history-positive/PST-negative and history-negative/PST-positive mismatches. Results, which will be published in detail in the medical literature later this year, showed that the skin test reagent is safe and effective for a definitive diagnosis of IgE-dependent latex allergy.1
Hamilton and colleagues have been working on developing a reagent since 1992.
"In the United States, we still don't have an FDA-licensed skin-testing material, so allergists can't do what they normally do, which is to diagnose using skin testing. They are sending in blood samples for serologic testing, which is the alternative," Hamilton explains. "The skin test is biologically the most relevant and diagnostically accurate test, and results are available in 15 minutes, as opposed to at least one to several days for blood test results."
Some allergists have resorted to making "home brews" from latex glove extracts to skin-test individuals, but this can be extremely dangerous to the patient.
"There are many problems with that," Hamilton says. "First, [the extract] is not characterized, so we don't know what the results of the test mean. We don't know what proteins are in it, what comes off the glove, or if what comes off the glove is representative of what the person has been exposed to. Also, it's potentially hazardous."
Skin-testing using uncharacterized reagents potentially can cause anaphylaxis and death, he notes.
Unlicensed skin tests also can give false-positive diagnoses, says B. Lauren Charous, MD, director of the allergy and respiratory care center at the Milwaukee Medical Clinic, and an allergist who diagnoses and treats many latex-allergic HCWs.
Charous says he recently evaluated a patient who had been diagnosed latex-allergic by another allergist using a homemade latex glove extract. The patient had become "very agitated" by the diagnosis, fearing what would happen if she had a latex reaction requiring hospitalization. Charous said he was suspicious of the diagnosis because the patient, who was not an HCW, had no risk factors or cross-reactions with foods often linked to latex allergies.
"I skin-tested her with a Canadian reagent and found she's negative," he says. "I did a glove challenge on her, and she's not latex-allergic. I don't fault the other [allergist]; he tried to do a good comprehensive evaluation, but it shows we need a reagent we can trust. We're exposing people to situations that can certainly be life-threatening and possibly lethal if they're allergic to latex. It's reasonable for them to know whether they're truly allergic."
Charous, who also is chairman of the latex hypersensitivity committee of the American College of Allergy, Asthma, and Immunology in Arlington Heights, IL, says Hamilton's data "look very good. As far as I can tell from the data presented, this is certainly promising. We need it. I would like to see [the reagent] either generally out, or at least in the hands of people with a lot of patients to get more experience with it."
Hamilton would like to see more rapid approval of the reagent, as well. He says he believes the adult HCW group has been "adequately evaluated," but the reagent has been tested on only 10 spina bifida children so far. He would like the FDA to approve the test for adults while he acquires more pediatric data.
"Whether they'll approve it for adults and not children is unclear. We had to show safety, efficacy, and composition, and that's what I believe we have done," he states. "This whole thing is just taking so long and is going in such slow stages, so I don't know precisely what's going to happen. The FDA process is very slow, and also the documentation of a reagent clinically is very difficult and takes time to do. It took a whole year to do the adult study, and I don't know how long it will take in children."
Whether the FDA would approve the product for adults while waiting for pediatric data is "a labeling issue," says Paul Turkeltaub, MD, a medical officer in the agency's Division of Allergenic Products and Parasitology.
While refusing to comment on anything specifically related to Hamilton's application, Turkeltaub says the speed at which the FDA approves a new product "depends on how fast people move the paper. Applications are reviewed, usually questions are raised, additional data or clarification may be needed. Most of these things do require a period of time to iron out."
Reference
1. Hamilton RG, Adkinson NF Jr., Multi-Center Latex Skin Testing Study Task Force. Diagnosis of natural rubber latex allergy: Multi-center latex skin testing efficacy study. Presented at the American Academy of Allergy, Asthma and Immunology 54th annual meeting. Abstract No. 682. Washington, DC; March 1998.
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