The goal of this clinical trial is to learn about the clinical efficacy and safety of ganciclovir (GCV) capsules in the treatment of refractory moderate-to-severe allergic rhinitis. The main questions it aims to answer are:

1. Whether ganciclovir improve nasal symptoms and life quality in patients with refractory moderate-to-severe allergic rhinitis.
2. Whether ganciclovir is safe for the treatment of allergic rhinitis.

Participants with refractory moderate-to-severe allergic rhinitis will be included in the trial based on the inclusion and exclusion criteria, and randomized into experimental and control groups.

The two groups will be treated with blinded ganciclovir capsules or placebo for two weeks, with the background therapy of mometasone furoate aqueous nasal spray. A placebo is a look-alike capsule that contains no active drug. Nasal symptom scores, nasal secretions, blood samples and adverse events will be collected during the visits.

Researchers will compare the experimental and control groups to see whether ganciclovir improve symptoms and is safe for the treatment of refractory moderate-to-severe allergic rhinitis.

Ganciclovir (GCV) is clinically used for the treatment of DNA viral infections. In clinical practice, we have found that patients with refractory AR have improved nasal symptoms after oral administration of ganciclovir. In clinical practice, we have found that patients with refractory AR have improved nasal symptoms after oral administration of ganciclovir. To further explore the role of GCV in the treatment of refractory allergic rhinitis, we have conducted an interventional non-randomised cohort study of GCV for refractory AR. The results found that 65% of all refractory AR patients included in the observation were effectively treated with GCV. Based on the previous discovery in the clinical practice, the conjecture is proposed that ganciclovir may improve symptoms in allergic rhinitis patients, in particular the patients with refractory moderate-to-severe allergic rhinitis. Thus, the randomized, double-blind, placebo-controlled clinical trial was designed to explore the validity of this hypothesis.

The research involves three phases: screening phase(Day-14±2~0)；baseline (Day1)；treatment phase (Day1~14)；follow-up phase (Day14~28).

In the screening phase, anterior rhinoscopy, serum specific IgE test, skin prick test, total nasal symptom scores (TNSS), visual analogue scale (VAS) scores, Allergic Rhinitis Control Test (ARCT) score will be performed for participants. Participants who meet the inclusion and exclusion criteria will enter the treatment phase and receive the medication for two weeks. At the end of the treatment, researchers will follow participants for two weeks to track efficacy and safety.

Researchers will collect participants' symptom scores, nasal secretions and blood. The biological specimens will be used to test for indicators that support the determination of therapeutic efficacy. Vital signs, blood routine examination, urine routines, liver function test, kidney function test and electrocardiograms will be measured for participants before and after treatment to assess the safety of ganciclovir.

The data collected will be statistically analyzed to examine the clinical efficacy and safety of ganciclovir capsules in the treatment of refractory moderate-to-severe allergic rhinitis.

Inclusion Criteria:

1. Aged between 18 and 65 years.
2. Diagnosed with moderate-to-severe perennial allergic rhinitis based on Chinese guideline for diagnosis and treatment of allergic rhinitis (2022, revision) with Allergic Rhinitis Control Test (ARCT) score <20.
3. Total Nasal Symptom Score (TNSS) ≥6 or at least two of the four subdomains(sneezing, rhinorrhea, nasal itching, and nasal obstruction) ≥2 at the time of both screening and randomization. And the improvement in TNSS was assessed as < 30% at randomization compared to screening.
4. The participant is allergic to dust mites or other perennial allergens
5. Voluntarily participate in the clinical trial and sign the informed consent.

Exclusion Criteria:

1. Participants with hypersensitivity to ganciclovir capsules and its excipients.
2. Have symptoms of viral infection, fever and other systemic symptoms in the past 2 weeks.
3. Pregnant or lactating women and participants who have pregnancy plan during the study period.
4. Participants with severe neutropenia (absolute neutrophil count less than 0.5*10^9/L) or severe thrombocytopenia (platelet count less than 2.5*10^10/L).
5. Comorbidities such as upper and lower respiratory tract infections, history of acute or chronic sinusitis, dry rhinitis, atrophic rhinitis, severe deviated septum and asthma.
6. Participants with other severe heart, lung, liver and kidney disease.
7. Participants who had received any live or attenuated vaccine within 4 weeks prior to baseline or intended to receive live or attenuated vaccine (or BCG treatment) during the study period or within 4 weeks after the last administration of the investigational drug product.
8. Participants with a history of HIV infection or who test positive for HIV serology.
9. Participants currently infected or chronically infected with hepatitis B virus (HBV) or hepatitis C virus (HCV).
10. Participants with cirrhosis and/or chronic hepatitis.
11. Participants who have been diagnosed with active parasitic infections or are at high risk of developing such infections.。
12. Participants with a known or suspected history of immunosuppression, including a history of invasive opportunistic infections (e.g., histoplasmosis, listeriosis, coccidioidomycosis, pneumosporidiosis, aspergillosis). Or participants with what researchers believe to be unusually frequent, recurring, or prolonged infections.
13. Participants with a known history of malignancy within 5 years prior to screening.
14. Participants with severe co-morbidities that, in the opinion of the investigator, would adversely affect their participation in this study.
15. Participants with combined neurological or psychiatric disorders who are unable or reluctant to cooperate.
16. Participants with disabilities prescribed by law (blind, deaf, mute, mentally challenged, mentally handicapped, etc.).
17. Participants suspected or having a history of alcohol and drug abuse.
18. Other participants who have been involved in other clinical trials within 3 months before the screening.
19. The researchers consider it inappropriate to participate in this clinical trial.