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Electrolyte structures and ionization conditions for iontophoretic drug formulation of local anesthetics
Uppsala University, Medicinska vetenskapsområdet, Faculty of Pharmacy, Department of Pharmaceutical Chemistry.
1999 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Iontophoresis is a modern method of drug delivery by which charged bioactive molecules (drugs) are transferred from an electrolytic reservoir into and through a tissue, normally skin, by means of a weak electric current. The drug is placed in a conductive medium, usually an aqueous solution or a hydrogel, between the "active" electrode and the skin. The circuit is completed by a second "passive" electrode and the skin. Although iontophoresis is a well-known method for transdermal delivery of drugs, basic physicochemical knowledge of this phenomenon is still lacking.

This thesis aimed to obtain a wide understanding of electrolyte structures and ionization conditions in iontophoresis, and a firm physicochemical basis for improvement of iontophoretic drug formulation of local anesthetics. The precision conductometric technique was used mainly. Lidocaine hydrochloride (LidHCl) was selected as a model local anesthetic substance. The conductance theory of Fuoss, Hsia and Fernandez-Prini was used to interpret the experimental data, with respect to ionization and mobility of LidHCl in different solvent media. LidHCl was studied in the following solvents:, water, propylene glycol (a transdermal enhancer),aqueous propylene glycol (20 weight-% PG) and 1-octanol. To compare the ionization properties of prilocaine hydrochloride (PrilHCl) with those of LidHCl, PrilHCl was studied in the same pharmaceutical aqueous-enhancer medium. Furthermore, the molecular diffusive transport properties of the local anesthetics lidocaine-, prilocaine-,bupivacaine-, etidocaine-, mepivacaine- and ropivacaine hydrochloride in an agarose hydrogel (1 weight-% agarose) were studied.

The results indicate that, for the solvents studied, LidHCl has the highest ionic mobility in aqueous propylene glycol; u(LidH+) = 1.35 mm2 V-1 min-1. No measurable difference in ionization properties and ionic mobility between LidHCl and PrilHCl in aqueous propylene glycol was observed. Within the concentration range investigated in this solvent, more than 98% of both LidHCl and PrilHCl are in ionized form (LidH+ and PrilH+). Of the six local anesthetics studied by diffusion measurements in agarose hydrogel (1 weight-% agarose) as medium, LidHCl and PrilHCl have the highest diffusion coefficients; D(lido) = 7.79 · 10-6 and D(prilo) = 7.76  · 10-6 cm2/s.

From a pharmaceutical point of view, it might be interesting to study the possibility of combining lidocaine- and prilocaine hydrochloride in an aqueous-enhancer medium as an iontophoretic drug formulation of local anesthetics.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 1999. , 36 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 0282-7484 ; 216
Keyword [en]
Pharmaceutical chemistry
Keyword [sv]
Farmaceutisk kemi
National Category
Medicinal Chemistry
Research subject
Physical and Inorganic Pharmaceutical Chemistry
URN: urn:nbn:se:uu:diva-1008ISBN: 91-554-4569-1OAI: oai:DiVA.org:uu-1008DiVA: diva2:160542
Public defence
1999-11-26, lecture hall B42, Biomedical Center, Uppsala, Uppsala, 10:15
Available from: 1999-11-05 Created: 1999-11-05Bibliographically approved

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