Good Practice in Postoperative and Procedural Pain Management ...

enhance systemic absorption. Lidocaine is included insome injections, such as depot corticosteroids, to preventpain and itching caused by local irritation.Prilocaine is an amide local anesthetic with a similarpotency to lidocaine. However, it has a slower onset ofaction, less vasodilator activity, and a slightly longerduration of action; it is also less toxic. Prilocaine isused for infiltration anesthesia and nerve blocks insolutions of 0.5%, 1%, and 2%. A 1% or 2% solutionis used for epidural anesthesia; for intravenous regionalanesthesia, 0.5% solutions are used. For dentalprocedures, a 3% solution with the vasoconstrictorfelypressin or a 4% solution without is used. A 4%solution with epinephrine (1 in 200 000) is also usedfor dentistry in some countries. Carbonated solutionsof prilocaine have also been used for epidural and brachialplexus nerve blocks. Prilocaine is used for surfaceanesthesia in a eutectic mixture with lidocaine EMLA.(ii) Doses, side effects, and toxicityThe dose of lidocaine depends on the site of injectionand the procedure but in general, the maximum doseshould not exceed 3 mgÆkg )1 (maximum 200 mg)unless vasoconstrictor is also used. Lidocaine hydrochloridesolutions containing epinephrine (1 in200 000) for infiltration anesthesia and nerve blocksare available; higher concentrations of epinephrine areseldom necessary, except in dentistry, where solutionsof lidocaine hydrochloride with epinephrine 1 in80 000 are traditionally used. The maximum dose ofepinephrine should be 5 microgm/kg )1 and of lidocaine5mgÆkg )1 . Epinephrine-containing solutions shouldnot be used near extremities such as for digital orpenile blocks. Lidocaine may be used in a variety offormulations for surface anesthesia. Lidocaine ointmentis used for anesthesia of skin and mucous membranes.Gels are used for anesthesia of the urinarytract and for analgesia of aphthous ulcers. Topicalsolutions are used for surface anesthesia of mucousmembranes of the mouth, throat, and upper gastrointestinaltract. For painful conditions of the mouth andthroat, a 2% solution may be used or a 10% spraycan be applied to mucous membranes. Eye drops containinglidocaine hydrochloride 4% with fluoresceinare used in tonometry. Other methods of dermal deliveryinclude a transdermal patch of lidocaine 5% forthe treatment of pain associated with postherpetic neuralgiaand an iontophoretic drug delivery system incorporatinglidocaine and epinephrine.Lidocaine is bound to plasma proteins, including a1-acid glycoprotein (AAG). The extent of binding is variablebut is about 66%. Plasma protein binding oflidocaine depends in part on the concentrations ofboth lidocaine and AAG. Any alteration in the concentrationof AAG can greatly affect plasma concentrationsof lidocaine. Plasma concentrations declinerapidly after an intravenous dose with an initial halflifeof