Mechanism of lidocaine release from carbomer–lidocaine hydrogels

✍ Scribed by Alvaro Jimenez-Kairuz; Daniel Allemandi; Ruben H. Manzo

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 138 KB
• Volume: 91
• Category: Article
• ISSN: 0022-3549
• DOI: 10.1002/jps.10036

✦ Synopsis

Rheology, acid-base behavior, and kinetics of lidocaine release of carbomer±lidocaine (CÀL) hydrogels are reported. A series of (CÀL) 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 À 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

The remaining species in the aqueous phase were distributed as: (L) 3.82%, (LH ) 14.5%, and [R-COO À LH ] 81.7%. Rheology and pH as a function of (CÀL) 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. (CÀL) 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 À 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.