Abstract
Lidocaine (LC) is a local anesthetic agent. The aim of this study is prolonging the anesthetic effect of this drug for transdermal delivery. Gels of LC hydrochloride were prepared with three different molecular weights (MW) and concentrations of chitosan. lecithin was used as permeation enhancer. Viscosity, bioadhesion, drug release from synthetic membranes, drug permeation through the biological barrier (rat skin) and antinocicetive effect of gels were studied. Increasing the concentration of chitosan caused to decrease the bioadhesion. Drug release studies in gels showed that increasing the concentration and MW of chitosan caused an increase in both the rate and extent and also in flux of drug probably because of the increase in repulsive forces between LC and chitosan cations. The flux of drug through the rat skin was higher for 3% high MW chitosan gel (H3) compared to the standard gel. LC was effective topically in hind paw formalin assay. It was most active immediately after its administration. The analgesic activity of LC in H3 gel could cover the duration of the formalin nociception. The maximal response of LC in comparable doses of H3 and standard gel was about 52% and 36% analgesia in the second phase, respectively compared to the control group. The higher response of the H3 gel may be attributed to the bioadhesive effect of chitosan base and the higher concentrations of LC compared to the standard gel.
Highlights
Transdermal and topical delivery of drugs provide advantages over conventional oral administration
The results show that if administered by means of gel, the same amount of LC gives significantly higher intracameral levels of LC, better analgesia, better patient cooperation, and less need for intraoperative supplemental anesthesia [11]
Materials LC hydrochloride as a gift from Daroupakhsh Pharmaceutical Company (Iran), Chitosan with different molecular weights (MW), formalin 37% solution, sodium hydroxide, and potassium dihydrogen phosphate were all purchased from Merck Chemical Company (Germany), LC marketed gel (2 w/w%) was used as the standard gel (Daroupakhsh Pharmaceutical Company, Iran)
Summary
Transdermal and topical delivery of drugs provide advantages over conventional oral administration. The molecule penetrates the viable epidermis before passing into the papillary dermis and through the capillary walls into systemic circulation It is the stratum corneum, a complex structure of compact keratinized cell layers that presents the rate limiting step and the greatest barrier to absorption of topical or transdermally administered drugs [1]. In trying to increase the anesthetic base concentrations, organic solvents have been used, but unacceptable local irritation prevented their clinical application Because of their poor penetration through intact skin, these solutions can be used only to anesthetize mucous membranes. Production of oil-in-water emulsion of single anesthetic agents may help in achieving relatively high concentrations of the active form with better skin penetration due to the presence of water. Materials LC hydrochloride as a gift from Daroupakhsh Pharmaceutical Company (Iran), Chitosan with different molecular weights (MW) (low MW 150000, intermediate MW 400000, and high MW 600000, Fluka, Switzerland), formalin 37% solution, sodium hydroxide, and potassium dihydrogen phosphate were all purchased from Merck Chemical Company (Germany), LC marketed gel (2 w/w%) was used as the standard gel (Daroupakhsh Pharmaceutical Company, Iran)
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