The study should create data for the selection of a clinically relevant endpoint to assess the potential of Buparid/PARI SINUS to postpone sinus surgery in patients with chronic Rhinosinusitis.

The objective of this study is to analyse whether Buparid/PARI SINUS has a higher potential to avoid or postpone sinus surgery in adult patients with CRS than Standard of Care therapy with Budes® Nasal Spray. The results of this study are expected to provide estimates for a proper sample size calculation to conduct a pivotal study.

Inclusion Criteria:

• Patient with confirmed diagnosis of chronic rhinosinusitis
• Patient without alternative other than sinus surgery
• Patient's written informed consent obtained prior to any screening or study-specific procedure
• Male or female, ≥ 18 years of age
• Patient is able to undergo nasal therapy without restrictions
• Capable to correctly use the PARI SINUS device
• Capable of understanding the purpose and risk of the clinical trial
• Female patients with childbearing potential must have a negative urine pregnancy test prior to first IMP administration.
• Patient is able to participate in the study according to Investigator's opinion

Exclusion Criteria:

• Patients with cystic fibrosis
• Patients with polyposis nasi grade I-IV
• Patients with prior FESS (Functional Endoscopic Sinus Surgery)
• Pregnant or breastfeeding women
• Any active invasive bacterial, viral or fungal infection within one week prior to first investigational medicinal product (IMP) administration
• No clinically relevant abnormal parameters of vital signs, blood biochemistry or renal/hepatic function
• Unlikely to comply with visits, inhalation procedures or other measurements scheduled in the protocol
• Receipt of an investigational drug as part of a clinical trial within 4 weeks prior to first administration of IMP
• Any co-existing medical condition that in the Investigator's judgement will substantially increase the risk associated with the patient's participation in the clinical trial
• Psychiatric disorders or altered mental status precluding understanding of the informed consent process and/or completion of the necessary procedures
• Drug or alcohol abuse
• End-stage malignancies
• Known hypersensitivity to Budesonide
• Patients with oral steroid therapy within the last 3 months
• Patients needing > 1 mg/day Budesonide (or steroidal equivalent) for therapy of asthma
• Patients on therapy with leukotriene-receptor antagonists, decongestants, antihistamines or antibiotics
• Patients with frequent epistaxis (> 1 episode per week)

Each participant has been monitored for adverse events up to 48 weeks. All patients withdrawn from the study will be followed-up for AEs or SAEs for further 2 weeks or 4 weeks, respectively.