Articles: anesthetics.
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Disordering, fluidizing and dilating effects of anesthetics upon cell membranes are well recognized. The fluidization can be precisely measured with phospholipid membranes. When phospholipids are dispersed in water, they form globules of bilayer structure. ⋯ The normalized values of the fluidizing action of these drugs at physiologic conditions correlated well with their nerve-blocking potencies. The present results indicate that the uncharged molecules fluidize the lecithin membrane by unsaturable nonspecific binding. The possible effect of the charged molecules upon the fluidity of natural membranes remains to be established.
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Plasma concentrations of local anaesthetic agents have been measured after 40 interscalene brachial plexus blocks in 39 patients, using lignocaine, prilocaine, bupivacaine and etidocaine. Lignocaine produced greater concentrations than prilocaine, and bupivacaine greater concentrations than etidocaine. The addition of adrenaline resulted in much lower concentrations in the case of all four agents.
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J. Pharmacol. Exp. Ther. · May 1977
Conduction-blocking concentrations of anesthetics increase with nerve axon diameter: studies with alcohol, lidocaine and tetrodotoxin on single myelinated fibers.
The equilibrium blocking concentrations of benzyl alcohol, lidocaine and tetrodotoxin just sufficient to block nerve impulse conduction were determined on myelinated single fibers of the bullfrog. For all three anesthetics it was found that the fastest conducting fibers (45 m/sec; about 18 micron diameter) required about 4 times higher blocking concentrations than the slowest fibers (8 m/sec; about 3 micron diameter). ⋯ J. Physiol. 10: 267-274, 1960), it is concluded that smaller myelinated fibers are more sensitive to anesthetic blockade.
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The clinical effectiveness and safety of compounded mixtures of lidocaine + bupivacaine and chloroprocaine + bupivacaine for either epidural or brachial-plexus block was studied in 48 adult patients. Of the several alternatives, chloroprocaine + bupivacaine with epinephrine was found the best choice for patients with typical plasma cholinesterase.
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The large number and diversity of anesthetic agents were evident to investigators 80 years ago, and suggested a physicochemical theory of anesthesia. Meyer and Overton were the first to offer a quantitative relationship between a physicochemical property and potency of anesthetic agents. They also focused attention on the lipid phase as the site of anesthetic action. ⋯ The microtubule theory of Allison and Nunn has not accumulated supporting evidence comparable to the lipid theories. Contradictory evidence makes any evaluation of this theory speculative. Additionally, the interspecies and intracellular variability of microtubules raises questions of the relevance of many studies...