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Effects of pH and ionic strength on catanionic drug-surfactant mixtures used for prolonged release from gels.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
2007 (English)In: Journal of drug delivery science and technology, ISSN 1773-2247, Vol. 17, no 4, 285-291 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study was to investigate the influence of pH and ionic strength on the phase behavior of two different catanionic drug-surfactant mixtures, and to study drug release from gels facilitated by the catanionic aggregates. Simplified phase diagrams were constructed for diphenhydramine or tetracaine mixed with SDS, varying the pH approximately between 6 and 11, and the NaCI concentration from 0.45 to 1.8%. The phases formed were studied visually, rheologically and with cryo-TEM. Some mixtures containing catanionic vesicles and micelles were selected for drug release studies from gels, varying the pH and NaCI concentration here as well. Both catanionic systems investigated proved relatively resilient to changes in the ionic strength. Changes in pH, on the other hand, caused marked effects to the phase behavior in both systems. The influence of pH was particularly strong in the drug-rich part of the tetracaine/SDS system, where increasing the pH causes precipitation. As expected, the drug release in both systems was somewhat affected by changes in both pH and ionic strength, but remained in all cases significantly prolonged as compared to the release of free, non-complexed, drug. These studies show that catanionic mixtures may be used to obtain prolonged drug release from gels, and that the concept also works when the gels are exposed to a pH that is a couple of units above the pKa of the cationic component. Furthermore, the ionic strength has no pronounced effect on the drug release, as long as it is kept within reasonable pharmaceutical levels.

Place, publisher, year, edition, pages
2007. Vol. 17, no 4, 285-291 p.
Keyword [en]
Microparticle, dosage form, anionic surfactant, pharmaceutical technology, micelle, vesicle, colloidal gel, controlled release form, mixture, cationic surfactant, drug, ionic strength, pH
National Category
Pharmaceutical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96414ISI: 000250032200009OAI: oai:DiVA.org:uu-96414DiVA: diva2:170981
Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2011-03-22Bibliographically approved
In thesis
1. Prolonged Drug Release from Gels, using Catanionic Mixtures
Open this publication in new window or tab >>Prolonged Drug Release from Gels, using Catanionic Mixtures
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of catanionic drug-surfactant mixtures was proven to be an efficient novel method of obtaining prolonged drug release from gels. It was shown that various commonly used drug compounds are able to form catanionic mixtures together with oppositely charged surfactants. These mixtures exhibited interesting phase behaviour, where, among other structures, vesicles and large worm-like or branched micelles were found. The size of these aggregates makes them a potential means of prolonging the drug release from gels, as only monomer drugs in equilibrium with larger aggregates were readily able to diffuse through the gel. When the diffusion coefficient for drug release from the formulation based upon a catanionic mixture was compared to that obtained for the drug substance and gel alone, the coefficient was some 10 to 100 times smaller.

The effects of changes in the pH and ionic strength on the catanionic aggregates was also investigated, and this method of prolonging the release was found to be quite resilient to variations in both. Although the phase behaviour was somewhat affected, large micelles and vesicles were still readily found. The drug release was significantly prolonged even under physiological conditions, that is, at a pH of 7.4 and an osmolality corresponding to 0.9% NaCl.

Surfactants of low irritancy, capric and lauric acid, may successfully be used instead of the more traditional surfactants, such as sodium lauryl sulfate (SDS), and prolonged release can still be obtained with ease.

Some attempts to deduce the release mechanism from the proposed systems have also been made using transient current measurements, dielectric spectroscopy, and modelling of the release using the regular solution theory. In these studies, the previous assumptions made concerning the mechanism responsible for the release were confirmed to a large extent. Only small amounts of the drug existed in monomer form, and most seemed to form large catanionic aggregates with the oppositely charged surfactant.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 66 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 65
Keyword
Pharmaceutics, gel, catanionic, vesicle, micelle, controlled release, diffusion, surfactant, drug delivery, Galenisk farmaci
Identifiers
urn:nbn:se:uu:diva-8303 (URN)978-91-554-7017-3 (ISBN)
Public defence
2007-12-07, B42, BMC, Husargatan 3, Uppsala, 09:15
Opponent
Supervisors
Available from: 2007-11-16 Created: 2007-11-16Bibliographically approved

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