title: Equilibrium properties and mechanism of kinetic release of metoclopramide from carbomer hydrogels.
abstract: Equilibrium properties and kinetics of metoclopramide release of carbomer-metoclopramide (C-M) hydrogels are reported. A set of (C-M)(X) (x=moles percent of M=50, 75, 100) that covers a pH range between 6.49 and 8.40 was used. Hydrogels exhibited a high negative electrokinetic potential (zeta). Concentrations of ion pair [R-COO(-)MH(+)] and free species [M] and [MH(+)] were determined by the selective extraction of M with 1,2-dichloroethane (DCE) together with pH measurements. The system (C-M) is characterized by a high proportion of drug present in the form of ion pairs and a negative zeta potential that attracts MH(+) and H(+) and repeals OH(-), providing a microenvironment of higher acidity than the bulk medium. Delivery rates of M were measured in a Franz type bi-compartmental device using water and NaCl 0.9% solution as receptor media. (C-M) hydrogels behave as a reservoir that releases the drug at a slow rate to water; the rate increases 14 times as water is replaced by NaCl solution. The pH effect on delivery rate suggests that, under the main conditions assayed, the rate of dissociation of R-COO(-)MH(+) together with the low change of pH in the polyelectrolyte environment are the factors that control releasing rates.
authors.affiliation: Departamento de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000, Cordoba, Argentina. alfejika@yahoo.com.ar
authors.forename: A F
authors.initials: AF
authors.lastname: Jimenez-Kairuz
authors.forename: D A
authors.initials: DA
authors.lastname: Allemandi
authors.forename: R H
authors.initials: RH
authors.lastname: Manzo
mesh_terms: D000180:Acrylic Resins / Q000008:administration & dosage*; D020100:Hydrogels; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008787:Metoclopramide / Q000008:administration & dosage* / Q000737:chemistry; D012995:Solubility
chemical_list: D000180:Acrylic Resins; D020100:Hydrogels; C006903:carbopol 940; D008787:Metoclopramide