Stabilization of a thermosetting emulsion system using ionic and nonionic surfactants

• Published in: International journal of pharmaceutics 1998-10, Vol.173 (1), p.103-116
• Main Authors: Scherlund, Marie, Malmsten, Martin, Brodin, Arne
• Format: Article
• Language: English
• Subjects: Anesthetics. Neuromuscular blocking agents; Biological and medical sciences; General pharmacology; Lidocaine; Medical sciences; Neuropharmacology; PEO-PPO-PEO block copolymers; Periodontal pocket; Pharmaceutical technology. Pharmaceutical industry; Pharmacology. Drug treatments; Prilocaine; Surfactants; Thermoreversible gelation
• ISSN: 0378-5173; 1873-3476; 1873-3476
• DOI: 10.1016/S0378-5173(98)00219-1

Ways of achieving a suitable local anesthetic formulation for use in the periodontal cavity were investigated in this study. By choosing poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers as excipients, formulations which are low viscosity fluids at room temperature and rigid elastic gels at body temperature are obtained. Despite the solubilizing capacity of these polymers, formulations containing Lutrol® F127 (EO 99PO 65EO 99) and the active ingredients lidocaine and prilocaine at the desired concentrations, i.e. approximately 25 mg g −1 of each component, are unstable. In order to achieve a more stable formulation a second surfactant can be added to the system since it could help both to solubilize the hydrophobic active ingredients and to stabilize the droplets of lidocaine and prilocaine from flocculation and coalescence. Thus, formulations containing local anesthetic compounds comprising the oil phase, a block copolymer giving the system unique rheological properties, and a suitable second surfactant were evaluated with regard to rheological behavior, drug release properties and stability. The system needs to be balanced regarding the concentration of polymer, active ingredients and surfactant in order to achieve a formulation with suitable properties. Stable formulations with appropriate characteristics for the application in focus here were obtained with anionic, cationic and nonionic surfactants.