A clinical study provides insight into one of the challenges of treating chronic rhinosinusitis.

Many people with chronic rhinosinusitis (CRS) receive one or more courses of oral antibiotics. While some patients improve, others experience only temporary relief or find that their symptoms persist despite treatment.

One possible explanation comes from a clinical study published in Xenobiotica, in which researchers investigated whether commonly prescribed oral antibiotics reach adequate concentrations within sinonasal mucus—the environment where many microorganisms associated with chronic rhinosinusitis are found.

The findings help explain why treating chronic rhinosinusitis can be more complex than simply prescribing an oral antibiotic.

What Is Chronic Rhinosinusitis?

Chronic rhinosinusitis is a long-lasting inflammatory condition affecting the nose and paranasal sinuses.

Unlike an acute sinus infection, CRS is a complex disorder that may involve multiple contributing factors, including:

• Chronic inflammation
• Altered mucociliary clearance
• Allergies
• Anatomical factors
• The nasal microbiome
• Biofilms in some patients

Because these factors vary between individuals, treatment often requires a combination of approaches rather than a single therapy.

The Role of Sinonasal Mucus

The surface of the nasal cavity and sinuses is covered by a thin layer of mucus that helps trap particles and microorganisms while supporting normal mucociliary clearance.

For medications intended to influence microorganisms within the nasal cavity, reaching this mucus layer may be an important consideration.

The researchers behind the Xenobiotica study asked a straightforward question:

Do oral antibiotics reach sufficient concentrations within sinonasal mucus?

The Study

Researchers from the University of Auckland evaluated two antibiotics commonly used in chronic rhinosinusitis:

• Doxycycline
• Roxithromycin

Rather than measuring only blood concentrations, they also measured antibiotic levels in:

• Blood (serum)
• Sinonasal tissue
• Sinonasal mucus

This allowed them to compare how much of each antibiotic reached different parts of the sinonasal environment.

What Did the Researchers Find?

The investigators found that both antibiotics achieved measurable concentrations in blood and sinonasal tissue.

However, concentrations within sinonasal mucus were substantially lower.

The average mucus-to-serum ratios were:

• Doxycycline: 0.16
• Roxithromycin: 0.37

These findings suggest that considerably less antibiotic reached the mucus than was present in the bloodstream.

The authors concluded that limited penetration into sinonasal mucus may be one factor contributing to the variable effectiveness of oral antibiotics in some patients with chronic rhinosinusitis.

Where Do Biofilms Fit In?

Biofilms are structured communities of microorganisms surrounded by a protective matrix.

Researchers have identified biofilms in a proportion of patients with chronic rhinosinusitis, although not every patient with CRS has biofilms, and their precise role continues to be investigated.

Laboratory studies suggest that microorganisms within biofilms may behave differently from free-floating organisms, leading researchers to investigate strategies that modify biofilm structure in addition to conventional antimicrobial approaches.

What Does This Mean for Treatment?

This study does not suggest that oral antibiotics are ineffective or should be avoided.

Instead, it highlights that chronic rhinosinusitis is a complex condition in which medication delivery, inflammation, microbial ecology, and individual patient factors all play important roles.

Current management of CRS may include combinations of approaches depending on the underlying cause and the individual patient, including:

• Saline nasal irrigation
• Intranasal corticosteroids
• Appropriate antibiotic therapy when indicated
• Management of allergies
• Endoscopic sinus surgery in selected patients
• Other treatments recommended by an ENT specialist

Researchers also continue to investigate topical formulations and strategies designed to interact directly with the nasal environment.

Ongoing Research into Topical Nasal Formulations

Because topical nasal products are delivered directly to the nasal cavity, researchers continue to investigate how different formulation ingredients interact with mucus, microbial communities, and biofilms.

Ingredients such as EDTA, xylitol, and other formulation components have been studied in laboratory models because of their physical or chemical properties. Additional clinical research is needed to determine how these findings translate into patient outcomes.

The Bottom Line

The University of Auckland study provides important insight into one of the challenges of treating chronic rhinosinusitis.

Although oral antibiotics reached therapeutic concentrations in blood and sinonasal tissue, substantially lower concentrations were found within sinonasal mucus. These findings suggest that medication delivery may be one factor influencing treatment outcomes in some patients.

As research into the nasal microbiome, biofilms, and topical nasal formulations continues to evolve, scientists are gaining a better understanding of the many factors that contribute to chronic rhinosinusitis and how future treatment strategies may be improved.

Reference

Siu J, Klingler L, Wang Y, et al. Oral antibiotics used in the treatment of chronic rhinosinusitis have limited penetration into the sinonasal mucus: A randomized trial. Xenobiotica. 2020.

FDA Disclaimer

This article is provided for educational and informational purposes only and summarizes findings from a published scientific study. It is not intended as medical advice and should not be interpreted as evidence that any ingredient or product diagnoses, treats, cures, or prevents disease. Treatment decisions for chronic rhinosinusitis should be made in consultation with a qualified healthcare professional.