title: Mechanism of lidocaine release from carbomer-lidocaine hydrogels.
abstract: Rheology, acid-base behavior, and kinetics of lidocaine release of carbomer-lidocaine (C-L) hydrogels are reported. A series of (C-L)(x) (x = mol% of L = 25, 50, 75, 100) that covers a pH range between 5.33 and 7.96 was used. Concentrations of ion pair ([R-COO(-)LH(+)]) and free species (L) and (LH(+)) were determined by the selective extraction of (L) with cyclohexane (CH) together with pH measurements, i.e., CH in a ratio CH/hydrogel 2:1 extracted 48% of the whole concentration of lidocaine [L(T)] of a (C-L)(100), [[L(T)] = ([R-COO(-)LH(+)]) + (L) + (LH(+))]. The remaining species in the aqueous phase were distributed as: (L) 3.82%, (LH(+)) 14.5%, and [R-COO(-) LH(+)] 81.7%. Rheology and pH as a function of (C-L) concentration are also reported. Delivery rates of free base L were measured in a Franz-type bicompartmental device using water and NaCl 0.9% solution as receptor media. (C-L) hydrogels behave as a reservoir that releases the drug at a slow rate. pH effects on rate suggest that, under the main conditions assayed, dissociation of [R-COO(-)LH(+)] is the slow step that controls releasing rates. Accordingly, release rate was increased upon addition of a second counterion (i.e., Na(+)), or through the diffusion of neutral salts such as NaCl, into the matrix of the gel.
authors.affiliation: Departamento de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000, Córdoba, Argentina.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Jimenez-Kairuz
authors.forename: Daniel
authors.initials: D
authors.lastname: Allemandi
authors.forename: Ruben H
authors.initials: RH
authors.lastname: Manzo
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry / Q000493:pharmacokinetics*; D000779:Anesthetics, Local / Q000737:chemistry / Q000493:pharmacokinetics; D002626:Chemistry, Pharmaceutical; D017220:Dentin-Bonding Agents / Q000737:chemistry / Q000493:pharmacokinetics; D004337:Drug Carriers / Q000737:chemistry / Q000493:pharmacokinetics; D020100:Hydrogels / Q000737:chemistry / Q000493:pharmacokinetics*; D008012:Lidocaine / Q000737:chemistry / Q000493:pharmacokinetics*; D012212:Rheology
chemical_list: D000180:Acrylic Resins; D000779:Anesthetics, Local; D017220:Dentin-Bonding Agents; D004337:Drug Carriers; D020100:Hydrogels; C006903:carbopol 940; D008012:Lidocaine