By mixing of hydrochloric acid and three uncharged local anesthetics (mepivacaine, bupibacaine, and dibucaine), respectively, we produced the coexisting state of uncharged and charged anesthetics in the aqueous solution and examined the competitive surface-adsorption of both anesthetics by measuring the surface tension and pH of aqueous solutions of hydrochloric acid-uncharged anesthetic mixture. The transferred quantities of respective uncharged and charged anesthetics into the surface-adsorbed film were evaluated by analyzing the experimental data thermodynamically. It was found that uncharged and charged anesthetics coexist only in the composition range more than 0.5. At the coexisting composition, the uncharged anesthetics transferred preferentially into the surface-adsorbed film rather than charged ones. The relative ease with which local anesthetics transferred into the surface-adsorbed film was proportional to the hydrophobicities and correlated the anesthetic potencies. The greater quantity of charged anesthetic exists in the aqueous solution in the physiological pH (ca. 7.4), however, the present results showed that the relation was reversed in the surface region under the same pH condition. The fact clearly implies that the surface-active molecule of local anesthetic in the physiological pH is the uncharged molecule.
|Number of pages||4|
|Journal||Anesthesia and Resuscitation|
|Publication status||Published - 2001|
All Science Journal Classification (ASJC) codes
- Anesthesiology and Pain Medicine