Solid-State Stability of Pentobarbital in Fast-Dissolving Suppositories: Implications for Dissolution Behavior and...

Safe and well-tolerated sedative formulations are essential in pediatric procedural care. Pentobarbital, a short-acting barbiturate, remains widely used for pediatric sedation. However, its oral administration is limited by poor palatability. Rectal administration therefore represents a relevant alternative, provided that formulation stability is ensured. This study evaluated the physicochemical and microbiological stability of fast-dissolving pentobarbital suppositories developed for pediatric use.

Suppositories containing 30 or 60 mg of pentobarbital sodium were formulated with two sodium hydroxide (NaOH) concentrations and stored under refrigerated (5°C) or frozen (-20°C) conditions for up to 180 days. Stability was assessed by macroscopic examination, pH measurement, dissolution testing, mechanical strength, softening time, and microbiological quality. Solid-state changes were analyzed using Raman spectroscopy and X-ray diffraction, and precipitation kinetics were modeled.

Refrigerated storage led to progressive precipitation from day 90, associated with pH decrease and conversion of pentobarbital sodium to its free acid, resulting in incomplete dissolution. In contrast, frozen storage preserved pH, physical integrity, and complete dissolution, even after 30 days at 5°C following thawing. Spectroscopic and diffraction analyses confirmed recrystallization under refrigeration, whereas frozen formulations retained an amorphous structure. Increased NaOH content delayed, but did not prevent, instability at 5°C. All formulations complied with pharmacopeial mechanical and microbiological requirements.

Storage temperature was the main determinant of stability, with freezing ensuring long-term preservation. NaOH buffering mitigated gelatin acidity and delayed drug conversion, thereby extending shelf life. These findings support further biopharmaceutical and clinical evaluation of pentobarbital suppositories for pediatric sedation.