For the millions who suffer from hay fever or asthma, a new under-the-tongue treatment may hold promise.
Pills and drops designed to desensitise the immune system to allergens could bring some of these allergy patients relief, a new research review finds.
The review pulled together 63 studies on so-called sublingual immunotherapy.
The therapy, commonly used in Europe and Asia, essentially allows people to get traditional allergy shots in the form of pills or drops that dissolve under the tongue. The principle is the same: Expose the immune system to extracts of the substance causing a person's allergy - grass pollen, for example - until it builds up a tolerance.
Right now, no under-the-tongue allergy products are approved in the United States. But some doctors offer the therapy anyway; they take the extracts approved for allergy shots and give them to patients to use orally.
What the research found
In the new review, researchers found "strong" evidence that under-the-tongue immunotherapy eased symptoms of allergy-induced asthma: In eight of 13 studies, patients saw more than a 40% improvement in symptoms, versus patients who either got a drug-free placebo or standard medication.
The evidence was weaker when it came to nasal allergies. Only nine of 36 studies showed a more than 40% drop in symptoms such as congestion, runny nose and itchy eyes.
Still, the majority of studies did show some benefit, said lead researcher Dr Sandra Lin, an associate professor of otolaryngology at Johns Hopkins University School of Medicine in Baltimore.
Under-the-tongue products are being evaluated for approval by the US Food and Drug Administration (FDA), and those results will be helpful, said Lin.
She said the results from European trials cannot be simply translated to the United States because of differences in the potency of the allergen extracts used.
"We need studies to see what are the most effective doses for US patients," Lin said.
The idea of taking pills instead of getting shots definitely appeals to patients, said Dr Harold Nelson, an allergy specialist at National Jewish Health in Denver, who wrote an editorial published with the study.
But his advice to US patients was to wait for products to be approved by the FDA.
Even if your doctor offers under-the-tongue immunotherapy, "there's no guarantee" it would be the same as the products studied in clinical trials, Nelson said. He noted that US doctors commonly give a patient a mix of different allergen extracts, because that's how it is done with allergy shots.
But the under-the-tongue products used in clinical trials have contained only a single allergen extract, Nelson said.
Like allergy shots, immunotherapy pills and drops take time to work. They need to be taken daily, for a few years. And they're not cheap, Nelson pointed out. They can cost $2 or more a day, and insurance companies may not cover it.
'Children fare as well as adults'
As far as safety, Lin said the trials her team reviewed found no serious allergic reactions to the immunotherapy. Most often, patients had "local" reactions, such as throat irritation and swelling or itching in the mouth.
"But we didn't do an exhaustive safety review," Lin stressed. It's possible that in the real world, some patients have had more serious reactions.
Another big question is whether under-the-tongue immunotherapy is as effective as traditional allergy shots, Nelson said. "It's not clear how they compare head-to-head," he said.
On the other hand, Lin said many more US patients will try immunotherapy if under-the-tongue options are approved. That's especially true of kids. "Who's going to be the least likely to accept allergy shots?" Lin said. "Young children."
Twenty of the studies her team reviewed focused solely on children. And kids seemed to fare as well as adults.
Current clinical trials in the United States are looking at under-the-tongue products for allergies to grass pollen, ragweed, cat dander and house dust mites. Lin suggested that for now, patients with allergies or allergy-induced asthma talk to their doctors about all their treatment options.
The study was funded by the US Agency for Healthcare Research and Quality. Nelson has received research funds from Circassia, Ltd., which is developing so-called T-cell vaccines to treat allergies.
Learn more about allergy immunotherapy from the American College of Allergy, Asthma and Immunology.