A new formulation of Pyrabital injection without urethane was proposed which contained 40% propylene glycol and had a pH approximately of 8.6. After autoclaving, it showed an excellent stability as well as good usability and safety in animal (rabbit) test. The approximate dissociation constants of barbital in various concentration of propylene glycol were determined. The solubility of barbital and aminopyrine in various concentration of propylene glycol and macrogol 400 at various temperatures were also determined. The critical pH value for the barbital to precipitate from the proposed injection solution was estimated to be 8.42 at 32℃.
Pyrabital injection has been one of most popular analgesics in clinical practice for more than 15 years in Taiwan medical circle. It had been a Japanese phamacopeia preparation for many years but was excluded from the pharmacopeia in 9th edition, 1976 because of containing carcinogenic solubilizing agent, urethane.1 Nevertheless, the constant demand for pyrabital injection is still very strong, at least in Taiwan medical circle. This communication presents a new approach to formulate a stable, safe and inexpensive pyrabital injection without the use of urethane and is suitable for intramuscular and intravenous injection. 本篇主要研究是著重於不使用urethane 而能調製Pyrabital注射液之處方設計。該處方含有40％之propylene glycol 而pH約為8.6。經高壓蒸氣滅菌，顯示優異之安定性，利用家兔之靜脈注射確認其安全性。在實驗過程中Aminopyrine 及Barbital 在各種propylene glycol濃液中之溶解度，及Barbital 在各種propylene glycol 濃度中之解離常數，皆經測定。Barbital從該pyrabital注射液析出沉澱之臨界pH值經推定為8.42(在32℃)。
