Stability of Levodopa/Carbidopa Rectal Suspensions.

Area of Science:

• Pharmaceutical Sciences
• Neurology

Background:

• Levodopa and carbidopa (L/C) combination therapy is standard for Parkinson's disease.
• Rectal administration of L/C is a viable alternative for patients with oropharyngeal dysphagia or when nasogastric tube insertion is not feasible.

Purpose of the Study:

• To determine the stability of two levodopa and carbidopa (L/C) rectal suspension formulations.
• To establish beyond-use dates for L/C rectal suspensions stored at 22°C and 5°C.
• To assess the impact of storage temperature on L/C rectal suspension stability.

Main Methods:

• Two L/C rectal suspension formulations were prepared and packaged in amber polypropylene bottles.
• Formulations were stored at 22°C and 5°C and analyzed over 35 days.
• Stability was assessed using a validated stability-indicating high-performance liquid chromatography (HPLC) method, alongside physical parameters like caking, resuspendability, and pH.

Main Results:

• Both formulations remained easy to resuspend with no caking or significant pH changes over 35 days.
• A glycerin-based formulation (formulation 1) showed reduced stability at 22°C (10 days) compared to formulation 2 (24 days).
• Both rectal suspensions demonstrated stability for 35 days when stored at 5°C.

Conclusions:

• The physical compatibility and chemical stability of L/C rectal suspensions varied by formulation and storage temperature.
• Refrigerated storage (5°C) extended the stability of both formulations to 35 days.
• Storage at 22°C yielded stability of 10-24 days, depending on the formulation.