Prilocaine, structure

Some other anesthetics with similar structures are prilocaine, tetracaine, ropivacaine, bupivacaine, chloroprocaine, and mepivacaine ... 

Figure 5.4 Structural formulae showing tertiary (lidocaine (lignocaine), bupivacaine) and secondary (prilocaine) amines. Asymmetrical carbon atom.

The introduction of a eutectic mixture of lidocaine (2.5%) and prilocaine (2.5%) (EMLa) bridges the gap between topical and infiltration anesthesia. The efficacy of this combination lies in the fact that the mixture of prilocaine and lidocaine has a melting point less than that of either compound alone, existing at room temperature as an oil that can penetrate intact skin. EMLA cream produces anesthesia to a maximum depth of 5 mm and is applied as a cream on intact skin under an occlusive dressing, for procedures involving skin and superficial subcutaneous structures (e.g., venipuncture and skin graft harvesting). EMLA must not be used on mucous membranes or abraded skin, as rapid absorption across these surfaces may result in systemic toxicity. 

Broadly speaking, it has been observed critically amongst all the known local anaesthetics , which are invariably employed in clinical practice, that there exists no clear-cut and obvious structure activity relationship in them. Besides, a plethora of these clinically prevalent and useful local anaesthetics are importantly tertiary amines , such as Butacaine, Bupivacaine, Dibucaine, Lidocaine, Mepivacaine, Prilocaine, Pramoxine, Proxymetacaine, Tetracaine etc. 

These local anesthetics, including lidocaine (Xylocaine), mepivacaine (Carbo-caine), Prilocaine (Citanest), and bupivacaine (Marcaine) are weak sensitizers, but allergic reactions are sporadically reported, e. g., lidocaine (Turner 1977). Recently Fregert et al. (1979) described two patients developing lidocaine allergy after 8 and 1 month use of Xyloproct ointment (lidocaine 5%, hydrocortisone acetate) they also had positive patch tests to related amide anesthetics, both to mepivacaine, one to bupivacaine and prilocaine. A positive reaction to the chemically unrelated cincaine was interpreted as concomitant sensitivity rather than cross-sensitivity. Safe substitutes for benzocaine-sensitive patients include lidocaine, mepivacaine, prilocaine, bupivacaine, and pyrocaine (Fisher 1973 p. 312), all based on an amide structure. Lidocaine-sensitive patients may use tetracaine (pontocaine), a derivative of aminobenzoic acid. 

One of the first uses of local anesthetics (LA) for anesthesia was in the late nineteenth century with William Halsted reporting a mandibular block and brachial plexus block using cocaine [37,38]. The chemical structure of local anesthetics in clinical use consists of an aromatic (lipophilic) benzene ring linked to an amino group (hydrophflic) via either an ester or an amide intermediate chain. The intermediate link classifies the local anesthetic as either an ester (procaine, chloroprocaine, tetracaine, and cocaine) or an amide (lidocaine, prilocaine, mepivacaine, bupi-vacaine, etidocaine, and ropivacaine). 

Chemical Structure lidocaine (hgnocaine), see Figure 68.1 prilocaine, see Figure 68.2... 

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