Standardized method for solubility and storage of capsaicin-based solutions for cough induction

Area of Science:

• Pharmacology
• Analytical Chemistry

Background:

• Inconsistent capsaicin solution preparation methods for cough induction challenge results.
• Tween improves capsaicin solubility and stability but imparts an unpleasant taste.
• Need for a standardized, Tween-free capsaicin solution for inhalation studies.

Purpose of the Study:

• Develop a standard method for preparing soluble and stable capsaicin solutions.
• Eliminate the need for Tween in capsaicin formulations.
• Create a safe and palatable capsaicin solution for cough induction.

Main Methods:

• Prepared capsaicin solutions (0-500 μM) in various solvents, with and without Tween.
• Assessed solution stability across four storage conditions: -20°C, 3°C, room temperature (protected from light), and room temperature (light-exposed).
• Quantified capsaicin via UV absorption and used Grubb's test for outlier removal.

Main Results:

• Tween offered a marginal increase in capsaicin solubility; however, complete solubility was not achieved with any tested system.
• Capsaicin solutions stored at 3°C, protected from light, demonstrated the highest stability, lasting a minimum of 30 weeks.
• Similar capsaicin concentrations were observed in solutions with and without Tween.

Conclusions:

• Recommend a 10% ethanol/water solvent system for preparing Tween-free capsaicin solutions.
• The proposed method accounts for incomplete solubility while ensuring a safe, stable, and palatable solution for inhalation.
• Standardized capsaicin preparation enhances the reliability of tussigenic challenge studies.