Ointment Bases

Abstract: Higuchi's equation that expresses the rate of release of medicaments from ointments containing drugs in suspension has long been used for its surprisingly simple form and convenience. If initial drug concentration is close to the solubility of the drug in the ointment base, however, accuracy of the equation is not always high. In order to improve the accuracy, explicit solution of Fick's laws with the appropriate boundary conditions was attempted.

Abstract: A new type of highly viscous ointment containing Carbopol-934 (CP) for application to the oral mucosa was formulated. The release properties of Brilliant Blue FCF (B.B.FCF) and the absorption of sodium salicylate through the oral mucosa from the ointment were studied. In release test using the agar gel bed method, there was no significant difference in % release of B.B. FCF after 12 h from ointments containing glycerin and polyethylene glycol (PEG) as excipients. However, the form of the ointment containing glycerin was maintained for 24 h whereas the ointment containing PEG liquefied. The 50% release time (T50) decreased with increase of glycerin content, but the difference of water absorption was negligible. Therefore, the release rate of B.B. FCF was related to the consistency of CP gel ointment rather than to water absorption. In vivo absorption of sodium salicylate from the ointment in hamster cheek pouch was also investigated. Absorption was fast from both 12.5 and 20% CP ointments, and the drug absorption was sustained for 5 h from 12.5% CP ointment.

Abstract: Selection of the base for an ointment should be made only after comparative evaluations of many factors, among which are: (a) drug-release characteristics, (b) consistency and body as defined by viscosity, tube extrusion pressure, penetrometer readings, spreadability, and effect of increased solids, (c) physical and chemical stability, and (d) handling and manufacturing characteristics. Methods for measuring some of these properties are described, and by such methods commonly used ointment bases are compared.