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Nefopam hydrochloride degradation kinetics in solution.
1Health Sciences Center, College of Pharmacy, University of Oklahoma, Oklahoma City 73190.
Journal of Pharmaceutical Sciences
|January 1, 1990
Summary
This study developed a HPLC method to analyze nefopam hydrochloride degradation. Nefopam hydrochloride shows maximum stability in aqueous solutions between pH 5.2-5.4, degrading via first-order kinetics.
Area of Science:
- Analytical Chemistry
- Pharmaceutical Chemistry
- Physical Chemistry
Background:
- Nefopam hydrochloride is a centrally acting non-opioid analgesic.
- Understanding its degradation pathways is crucial for pharmaceutical formulation and stability.
Purpose of the Study:
- To develop a stability-indicating analytical method for nefopam hydrochloride.
- To investigate the degradation kinetics and pH-rate profile of nefopam hydrochloride in aqueous solutions.
Main Methods:
- Reversed-phase high-performance liquid chromatography (RP-HPLC) was employed.
- Accelerated degradation studies were conducted across a pH range (1.18-9.94) at elevated temperatures (90°C).
- Spectrophotometric titration was used to determine the pKa value.
Main Results:
- A stability-indicating RP-HPLC method was successfully developed.
- Degradation followed apparent first-order kinetics.
- Maximum stability was observed at pH 5.2-5.4.
- The pKa of nefopam hydrochloride was determined to be 8.98 ± 0.33 at 25°C.
- Specific catalytic rate constants for hydrogen ion, water, and hydroxyl ion were quantified.
Conclusions:
- The developed HPLC method is suitable for stability testing of nefopam hydrochloride.
- The study elucidates the pH-dependent degradation kinetics, identifying optimal pH conditions for stability.
- Hydroxyl ion significantly influences degradation, with a greater effect on the protonated form.