Local anesthetics are among the most widely used drugs. Their development over the past century ranges from a documented influence on Freud's Interpretation of Dreams 1 to the synthesis of the ubiquitously popular lidocaine, as described in Chapter 1. For surgical procedures the use of regional, epidural and intrathecal local anesthesia has increased continuously during the past decade. Local anesthetics are also applied by physicians to ameliorate unpleasant sensations and reactions to other procedures, such as tracheal intubation. The presence or the threat of cardiac arrhythmias is often countered by chronic administration oflocal anesthetic-like agents, such as lidocaine or procainamide. Relief of acute pain, accompanying dental manipulations, for example, and of chronic pain are also accomplished with traditional local anesthetics. And over-the-counter formula tions of topical local anesthetics provide practitioners of solar indiscretion welcome relief from their otherwise unaccommodating sunburn. In all these applications the final effect of the local anesthetic is an inhibition of electrical activity, accomplished as a reduction or total blockade of action potentials. The primary site of action is the sodium channel, a transmembrane protein which is essential for the influx of sodium ions that subserves impulse generation and propagation in nerves, skeletal muscle, and heart. The detailed mechanisms oflocal anesthetic action are still being investigated and Chapter 2 of this volume provides a current overview of that subject.
Table of Contents1 Some Aspects of the History of Local Anesthesia.- A. Introduction.- B. Freud, Koller and the Early History of Cocaine.- C. Structure and Synthesis of Local Anesthetics.- D. Epinephrine and Local Anesthesia.- E. Toxicity of Local Anesthetics.- F. The Nervous Impulse and the Action of Local Anesthetics.- G. Pharmacokinetics of Local Anesthetics.- H. Summary and Conclusions.- References.- 2 The Action of Local Anesthetics on Ion Channels of Excitable Tissues.- A. Introduction.- B. Physiological Basis of Generation of the Action Potential.- I. Role of Ion Channels.- II. Kinetic Properties of Sodium Channels.- III. Gating Currents.- IV. Pharmacological Dimensions of the Sodium Channel.- C. The Action of Local Anesthetics on Sodium Channels.- I. Distribution of Local Anesthetics and the Mechanism of Their Blocking Action.- II. The Modulated Receptor Hypothesis: Past and Present Formulations.- D. Current Questions in Local Anesthetic Action.- I. Location of Local Anesthetic Binding Site(s) in the Sodium Channel.- II. Factors that Determine Rates of Action and Potencies of Local Anesthetics.- III. The Number and Nature of Local Anesthetic Binding Sites.- E. New Kinds of Local Anesthetic Agents.- F. Effects of Local Anesthetics on Potassium Channels.- G. Conclusion.- References.- 3 Structural Elements which Determine Local Anesthetic Activity.- A. Introduction.- I. Scope of Review and Methodology.- II. Measurements of Anesthetic Action.- B. Structure and Physico-Chemical Properties of Local Anesthetics.- C. Resolution of Structural Contributions to Potency.- I. Aromatic Groups.- II. Amide, Ester, and Ether Bonds.- III. Intermediate Alkyl Chain.- IV. Terminal Amine.- V. Stereoisomers.- VI. Onset and Duration of Action.- D. Comparisons of Nerve Blocking Actions with Antiarrhythmic Actions of Local Anesthetics.- I. Sensitivity of Nerve Versus Muscle.- II. Different Inactivation Gating in Nerve and Heart.- III. Factors Determining Potency in Heart.- IV. Relevance to Cardiotoxicity.- V. Importance of Intermediate, Open and Inactive Channel Blocking.- E. Models for Local Anesthetic Receptors.- I. Kinetic Models of Local Anesthetic Action.- II. Physico-Chemical Models.- III. Anesthetic Action and Channel Structure.- IV. Molecular Substrate for the Block Recovery Process.- References.- 4 Mechanisms of Differential Nerve Block.- A. Introduction.- B. Historical Discussion.- I. Differential Tonic Block.- II. Origins of the Dominant Paradigm.- III. Synthesis: The Size Principle.- C. Confirmations, Extensions, Clarifications, and Contradictions.- I. Confirmation and Extension of the Size Principle.- II. Contradictions of the Size Principle; Importance of Additional Factors.- D. Summary and Conclusion.- I. The Notion of Functional Specificity.- II. A Distributed Model of Conduction Safety.- References.- 5 Pharmacokinetics of Local Anesthetics.- A. Introduction.- B. Factors Affecting the Interpretation of Local Anesthetic Blood Concentrations.- I. Units of Expression.- II. Sampling Site.- III. Plasma Protein Binding.- C. Metabolism.- I. Ester Type Local Anesthetics.- II. Amide Type Local Anesthetics.- D. Pharmacokinetics in Man.- E. Factors Affecting Pharmacokinetics of Local Anesthetics.- I. Lung Uptake of Local Anesthetics.- II. Age.- III. Other Drugs.- IV. Disease.- V. Other Factors.- F. Pharmacokinetics in Experimental Animals.- References.- 6 Toxicity and Systemic Effects of Local Anesthetic Agents.- A. Effects on the Central Nervous System.- B. Effects on the Cardiovascular System.- I. Cardiac Effects.- II. Peripheral Vascular Effects.- C. Effects on the Neuromuscular Junction.- D. Miscellaneous Effects.- E. Other Toxicological Effects.- F. Treatment of Systemic Toxicity.- G. Local Tissue Toxicity.- H. Summary.- References.- 7 The Role of Local Anesthetic Effects in the Actions of Antiarrhythmic Drugs.- A. Introduction.- B. Electrophysiology of Cardiac Fibers.- I. Description of the Cardiac Action Potential.- II. Fast Responses and Slow Responses.- III. Excitability, Refractoriness, and Responsiveness.- C. The Effects of Local Anesthetics on Cardiac Fibers.- I. Effects on Fast Inward Sodium Current.- II. Effects on Action Potential Duration.- III. Effects on Phase 4 Depolarization and Normal Automaticity.- D. Antiarrhythmic Effects of Local Anesthetic Agents.- I. Classification of Arrhythmias.- II. Arrhythmias Due to Altered Impulse Initiation.- III. Reentrant Rhythms.- E. Conclusion.- References.- 8 Central Effects of Local Anesthetic Agents.- A. Introduction.- B. Routes of Entry of Local Anesthetic Agents into the CNS.- C. Behavioral Pharmacology of Local Anesthetic Agents.- I. Animal Studies of Locomotor Activity, Behavior and Correlative Neural Activity.- II. Effects of Local Anesthetics on Conditioned Behavior.- III. Behavioral Effects of Local Anesthetics in Man.- D. Effects of Local Anesthetics on Electrical Activity of the Brain.- I. The Convulsant Properties of Local Anesthesia.- E. Anticonvulsant Properties of Local Anesthetics.- F. Temporal and Spatial Effects of Local Anesthetics at Regional CNS Sites.- I. The Amygdaloid Complex as the Initial CNS Target of Local Anesthetics.- II. Anatomy and Function of the Amygdaloid Complex.- III. Other CNS Structures Affected by Local Anesthetics.- G. The Mechanisms Underlying Local Anesthetic-Induced Seizures.- I. Local Anesthetic Induced Disinhibition of Neuronal Pathways.- II. The Interplay of Local Anesthetics and Putative Neurotransmitters and Neuromodulators.- H. Central Nervous System Metabolic Effects of Local Anesthetics.- I. Summary.- References.