Dose-finding study of sublingual immunotherapy with phleum pratense extract (vs sodium chloride) in patients with grass pollen allergic rhinitis

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What is this study about?

The study focuses on Allergic rhinitis caused by grass pollen, a condition that produces sneezing, runny nose, itchy eyes and throat. The treatment being tested is a sublingual (under‑the‑tongue) spray containing the grass pollen extract phleum pratense at three different strengths: Vacuna Phleum pratense 1000 TBU/ml, Vacuna Phleum pratense 3000 TBU/ml and Vacuna Phleum pratense 6000 TBU/ml. A matching Placebo spray containing only sodium chloride is also used for comparison. The purpose of the trial is to find the dose that works best without compromising safety.

Participants will receive the assigned spray daily for a set period, while regular visits will include a simple nose test (nasal provocation test) to see how the nose reacts, and a quick breathing measurement called Nasal Inspiratory Peak Flow. Blood samples will be taken at the start and at the end to check levels of antibodies such as IgE and IgG4. Throughout the study, any side effects will be recorded, and standard rescue medicines may be used if needed. The overall length of involvement is several months, with regular check‑ins to monitor health and response.

1 baseline assessment and randomization

after enrollment, a baseline visit is scheduled. during this visit, a nasal provocation test is performed using phleum pratense powder (0.8 ml nasal spray). the result of this test serves as the reference for later comparisons.

blood samples are taken to measure specific antibodies (ig e and ig g4) against phleum pratense. a skin prick test with the same allergen is also conducted.

based on the study protocol, the participant is randomly assigned to receive either placebo (sodium chloride) or one of the three phleum pratense sublingual sprays (1000, 3000 or 6000 tbu/ml).

2 initiation of sublingual treatment

the assigned sublingual spray (0.2 ml per dose) is taken under the tongue as instructed by the study protocol. the spray may be a placebo (sodium chloride) or a phleum pratense extract at 1000, 3000 or 6000 tbu/ml.

the participant continues this administration for the entire study period, which lasts from september 2026 to april 2027 (approximately eight months). the exact frequency (for example, daily) follows the schedule defined in the study documents.

3 routine monitoring visits

regular clinic visits are scheduled throughout the treatment phase. at each visit, the investigator records any local or systemic reactions, symptoms related to allergic rhinitis, and the use of rescue medication.

participants are instructed to avoid taking rescue medication unless required for symptom control; any rescue medication taken is documented.

if adverse reactions occur, the study protocol specifies the actions to be taken, but these are handled by the clinical staff.

4 final assessment

at the end of the study (april 2027), a final nasal provocation test with phleum pratense powder (0.8 ml) is performed to compare the response with the baseline result.

blood samples are drawn again to assess changes in specific Ig e and Ig g4 levels to phleum pratense.

a repeat skin prick test with the allergen is carried out for comparative analysis.

the participant returns the remaining study medication and completes any final questionnaires required by the protocol.

Who Can Join the Study?

Be between 12 and 50 years old.
Have a doctor‑diagnosed allergic rhinitis (runny, sneezing nose) that may also include conjunctivitis (eye irritation) and may or may not include asthma (breathing trouble). If you have asthma, a breathing test must show that your FEV1 (the amount of air you can force out in one second) is more than 70% of what is expected for your age and size, and your FVC (total amount of air you can exhale) is more than 80% of expected.
Have a positive skin prick test to the grass pollen *Phleum pratense* or a similar grass, meaning a small raised bump (wheal) at least 5 mm larger than the control spot, with the test done no more than 6 months ago.
Show a blood level of specific IgE (a type of allergy antibody) to the same grass pollen of at least 0.70 kU/L, measured within the last 6 months and confirmed by the study laboratory.
Have a positive result on a nasal provocation test, where a small amount of the pollen is placed in the nose and causes a reaction at a concentration no higher than 1 part pollen to 10 parts solution.
Sign an informed consent form agreeing to take part in the study.
If you are a woman who could become pregnant, you must not be pregnant when the study starts (proved by a negative urine pregnancy test) and must take another pregnancy test at the end of treatment.
Not have received any specific allergy treatment (immunotherapy) with Phleum pratense pollen or related pollen in the past 5 years, and you must not receive any such treatment during the study.

Who Cannot Join the Study?

Having a positive skin test or blood test for year‑round allergens such as animal dander, mold, storage mites, or other local allergens that could affect your symptoms during the study (a skin prick test is a tiny poke on the skin to check for allergy, and a specific IgE test measures allergy‑related antibodies in the blood). If you are allergic to animals but never have contact with them, you may still be allowed.
Being allergic to certain trees (Cupressus arizonica, ash, plane tree, or oak) whose pollen season overlaps with the study period, in addition to grass pollen.
Showing nasal hyperreactivity, which means a drop of at least 15 % in the amount of air you can breathe through your nose (measured by Peak Nasal Inspiratory Flow) or a rise of 3 points in symptom scores during a nasal provocation test (a test that briefly exposes the nose to an allergen).
Having had nasal or oral surgery within the past 6 months, or recent dental work such as extractions or implants within the past 2 months.
Having a hole in the nasal septum (the wall that separates the two sides of the nose).
Having partially controlled or uncontrolled asthma, defined by lung‑function tests showing FEV1 ≤ 70 % of the expected value and FVC ≤ 80 % of the expected value, or needing continuous high‑level asthma medication (GINA levels 3‑5). FEV1 and FVC are measurements of how much air you can forcefully exhale.
Having any standard reason to avoid allergy shots, such as active or recent cancer diagnosed in the last 5 years, a serious mental health condition that limits daily activities, being pregnant, or breastfeeding.
Regularly taking medicines that would interfere with study results, such as antihistamines, oral or injected corticosteroids (steroid drugs that reduce inflammation), membrane stabilizers like cromoglycates, or antidepressants.
Refusing to join the trial or to sign the informed consent form, which is the written agreement to participate.
Being known to be allergic to any ingredient in the study medication other than the grass pollen itself.

Where you can join this trial?

Verified and Recommended Sites

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Verified Sites

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Other Sites

Site Name	City	Country
Hospital Universitario De Fuenlabrada	Fuenlabrada	Spain
Hospital General Universitario De Albacete	Albacete	Spain
Hospital Universitario de Cuenca	Cuenca	Spain
Hospital Universitario De Leon	Leon	Spain
Hubvkrjs Uxizgabqbmyty Dc Lj Pnutmgqb	Madrid	Spain
Plqh Cdtzem Gqqq	Barcelona	Spain
Hypetfbg Ds Lc Siqvc Cljh I Sueu Pam	Barcelona	Spain

Trial status

Country	Status	Recruitment Start
Spain	Not yet recruiting	01.09.2026

Trial locations

Investigated drugs:

Phleum pratense sublingual spray (low dose) is a liquid medicine that contains a small amount of grass pollen extract. It is sprayed under the tongue, where it is absorbed through the mouth lining. In this trial the low‑dose spray is used to see if a small amount of the extract can safely reduce allergy symptoms over time.

Phleum pratense sublingual spray (medium dose) is a liquid medicine that contains a moderate amount of grass pollen extract. Like the low‑dose version, it is placed under the tongue as a spray. The purpose of the medium dose is to find out whether a larger amount works better at controlling allergy symptoms while still being safe for participants.

Phleum pratense sublingual spray (high dose) is a liquid medicine that contains a higher amount of grass pollen extract. It is also administered as a spray under the tongue. This form tests whether a higher concentration can provide the most effective allergy relief without causing important side effects.

Nasal provocation test with Phleum pratense is a procedure that uses a powdered form of the grass pollen extract placed in the nose. The test helps researchers measure how strongly a person reacts to the allergen before and after the sublingual treatment, giving a clear picture of how well the therapy works.

Investigated diseases:

Seasonal allergy

Allergic rhinitis caused by grass pollen – This is an allergic reaction that affects the nose when a person breathes in tiny particles from grass pollen. It begins with sneezing, a runny or blocked nose, and an itchy feeling inside the nostrils. Over time, symptoms may become more frequent during the grass pollen season and can spread to the eyes, causing watery and itchy eyes. The inflammation can make the nasal passages swell, which may lead to a feeling of pressure in the face. Without avoidance of the allergen, the condition tends to persist as long as exposure continues.

Trial ID:

2025-522730-31-00

Protocol code:

APISLIT-DD-G-2025-01

Trial Phase:

Therapeutic exploratory (Phase II)

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Dose-finding study of sublingual immunotherapy with phleum pratense extract (vs sodium chloride) in patients with grass pollen allergic rhinitis

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?