Résumé
An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into two broad classes: general anesthetics, which result in a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body without necessarily affecting consciousness. A wide variety of drugs are used in modern anesthetic practice. Many are rarely used outside anesthesiology, but others are used commonly in various fields of healthcare. Combinations of anesthetics are sometimes used for their synergistic and additive therapeutic effects. Adverse effects, however, may also be increased. Anesthetics are distinct from analgesics, which block only sensation of painful stimuli. Local anesthetic Local anesthetic agents prevent the transmission of nerve impulses without causing unconsciousness. They act by reversibly binding to fast sodium channels from within nerve fibers, thereby preventing sodium from entering the fibres, stabilising the cell membrane and preventing action potential propagation. Each of the local anesthetics has the suffix "–caine" in their names. Local anesthetics can be either ester- or amide-based. Ester local anesthetics (such as procaine, amethocaine, cocaine, benzocaine, tetracaine) are generally unstable in solution and fast-acting, are rapidly metabolised by cholinesterases in the blood plasma and liver, and more commonly induce allergic reactions. Amide local anesthetics (such as lidocaine, prilocaine, bupivacaine, levobupivacaine, ropivacaine, mepivacaine, dibucaine and etidocaine) are generally heat-stable, with a long shelf life (around two years). Amides have a slower onset and longer half-life than ester anesthetics, and are usually racemic mixtures, with the exception of levobupivacaine (which is S(-) -bupivacaine) and ropivacaine (S(-)-ropivacaine).
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