PHARMACODYNAMICS OF LOCAL-ANESTHETICS

The present review points out the present state of pharmacodynamics of local anesthetic agents, After briefly repeating the basic elements o f the anatomy and physiology of neurons, the mode of action of local a nesthetics is shown, The two possibilities for their action, the ionic form from the cells' interior side after passing the membrane and the uncharged form working by a swelling effect in the cells' membrane ar e discussed, The concept of the minimal blocking concentration Cm, whi ch was found to be necessary, in vitro to block impulse conduction is explained, Thereafter some reasons are mentioned as to why it may be d ifficult in some circumstances to reach the Cm in a nerve in practice. The different substances in clinical use are listed and their onset a nd duration of action is mentioned, The dynamics of a nerve blockade i s shown discussing the possibilities of altering them by adding a vaso constrictor or carbon dioxide. The time passing from the first event o f pain until the re-supply with local anesthetic seems to be the main determinant for development of tachyphylaxia. The main actions of the local anesthetics, their side-effects and their interaction with other xenobiotics are discussed in the next chapter. The role of bupivacain e- and etidocaine- related cardiotoxicity is emphasized. The reason fo r this phenomenon should be the long dissociation time constant from t he heart's natrium channel. Finally a short outlook with respect to ro pivacaine is made, also mentioning EMLA- cream and miscellanous applic ation forms of local anaesthetics.