Introduction
At EXPERTA | TESTING, we have a premium partnership with a lab specialized in designing and executing complex pharmacokinetic (PK) studies to evaluate the safety, efficacy, and bioavailability of novel drug formulations.
Recently, we collaborated on a groundbreaking project to assess the systemic bioavailability and potential drug–drug interactions of a fixed-combination nasal spray containing two active pharmaceutical ingredients (APIs).
This case study highlights our approach to addressing critical questions in formulation development while ensuring regulatory compliance and patient safety.
The Challenge: Evaluating a Novel Combination Therapy
Allergic rhinitis (AR) is a widespread condition affecting hundreds of millions globally, with symptoms ranging from nasal congestion to impaired sleep and productivity.
While intranasal corticosteroids and antihistamines are established first-line treatments, combination therapies are increasingly explored to improve symptom control and patient adherence.
However, developing a fixed-combination nasal spray introduces unique challenges:
- Potential pharmacokinetic interactions between APIs.
- Formulation-based alterations in bioavailability.
- Regulatory requirements for demonstrating systemic safety, particularly when combining with low systemic exposure margins.
Our client sought to validate whether their novel aqueous nasal spray formulation could deliver consistent, predictable PK profiles for both APIs without compromising safety or efficacy.
Our Approach: Rigorous PK Study Design
To address these challenges, we designed two randomized, crossover studies in healthy volunteers, leveraging highly sensitive LC-MS/MS assays to quantify API concentrations at therapeutic doses.
This approach avoided the pitfalls of earlier studies, which relied on supra-therapeutic doses due to assay limitations.
Indicational image of HPLC-MS-MS - Canva
Study 1: Assessing API-1 Bioavailability
- Objective: Compare the PK profile of API-1 in the combination product vs. its single-entity counterparts (a formulation-matched mono-product and a marketed comparator).
- Design:
- Three-period, six-sequence crossover with a washout interval of ≥10 days.
- Dosing: Two sprays per nostril (therapeutic dose).
- Sampling: Serial blood samples collected over 24 hours to capture the full PK profile, including a tri-exponential decline phase - a previously undocumented finding due to improved assay sensitivity.
- Key Parameters:
- Peak exposure (Cₘₐₓ)
- Total exposure (AUC₀₋ₜₗₐₛₜ)
- Time to peak concentration (tₘₐₓ)
- Elimination half-life (t₁/₂)
Study 2: Assessing API-2 Bioavailability
- Objective: Evaluate whether the presence of API-1 or the combination formulation altered the PK of API-2 compared to its mono-product and marketed comparator.
- Design:
- Identified sampling schedule based on the ~20-hour half-life of API-2, with samples collected up to 120 hours post-dose.
- Sensitivity: LC-MS/MS assay with a lower limit of quantification (LLOQ) of 2.0 pg/mL, ensuring accurate detection at therapeutic doses.
Analytical Excellence
- LC-MS/MS Assays: Validated for API-1 (LLOQ: 0.25 pg/mL) and API-2 (LLOQ: 2.0 pg/mL), with inter-assay coefficients of variation (CV) below 8% and accuracy within ±3%.
- Pharmacokinetic Analysis: Non-compartmental methods using validated software (e.g., FUNCALC 3) to calculate primary PK parameters.
- Statistical Rigor:
- ANOVA for crossover design, with log-transformed Cₘₐₓ and AUC data.
- 90% confidence intervals (CIs) for treatment ratios to assess bioequivalence boundaries (predefined as 50–200% for clinical safety).
Overcoming Technical Hurdles
- Low Systemic Exposure:
- Both APIs exhibited extremely low systemic bioavailability (e.g., <2% for API-1), requiring ultra-sensitive assays to detect trace concentrations.
- Solution: Deployed LC-MS/MS with about 40 to 80-fold improved sensitivity over traditional methods, enabling therapeutic-dose studies.
- Biphasic Absorption Profiles:
- API-1 displayed a double-peak phenomenon, suggesting biphasic nasal absorption (rapid dissolution of soluble fraction + sustained release from suspended particles).
- Implication: Formulation characteristics (e.g., droplet size distribution, viscosity, spray volume) likely influenced mucosal deposition and absorption.
- Regulatory Compliance:
- Aligned with EMA guidelines for fixed-combination products, ensuring:
- No clinically meaningful PK interactions between APIs.
- Comparable exposure to marketed mono-products.
- Safety margins for systemic exposure (e.g., >8-fold below thresholds for adrenal suppression).
Why This Matters for Drug Development
This project underscores the importance of early-phase PK studies in:
- De-risking formulation development by identifying potential interactions or bioavailability issues.
- Optimizing nasal spray performance through biopharmaceutical insights (e.g., spray pattern, droplet size, viscosity).
- Supporting regulatory submissions with robust, assay-sensitive data at therapeutic doses.
At EXPERTA | TESTING, we combine our scientific rigor, with cutting-edge analytics, and regulatory expertise at our premium partners to help clients navigate the complexities of combination product development.
Whether it’s nasal sprays, inhalers, or other localized therapies, our tailored PK studies provide the clarity needed to advance innovations safely and efficiently.
⇒ How can we support your next formulation challenge?
Contact our team to discuss tailored PK/PD solutions for your drug development program.