Local anesthetics, specific agents

Specific Local Anesthetic Agents. Clinically used local anesthetics and the methods of appHcation are summarized in Table 5. Procaine hydrochloride [51-05-8] (Novocain), introduced in 1905, is a relatively weak anesthetic having along onset and short duration of action. Its primary use is in infiltration anesthesia and differential spinal blocks. The low potency and low systemic toxicity result from rapid hydrolysis. The 4-arninobenzoic acid... 

Most local anesthetic agents consist of a lipophilic group (eg, an aromatic ring) connected by an intermediate chain via an ester or amide to an ionizable group (eg, a tertiary amine) (Table 26-1). In addition to the general physical properties of the molecules, specific stereochemical configurations are associated with differences in the potency of stereoisomers (eg, levobupivacaine, ropivacaine). Because ester links are more prone to hydrolysis than amide links, esters usually have a shorter duration of action. 

The method of drug administration or exposure to a poison may impart selectivity to a xenbiotic. For example, atropine can be applied directly to the eye for the dilation of the pupils. Note that eventual absorption into the blood stream from this site will cause systemic effects. Another example would be the topical (skin) application of a local anesthetic such as benzocaine. Monoclonal antibodies, which are specific for chemical functional groups, are tissue and cell-specific natural agents to which drugs can be chemically bonded. 

Anesthetic agents are a diverse class of chemicals which are extremely important in modern medicine. They are generally used to produce a loss of sensation to all stimuli, either in a specific anatomical area, or a total loss of consciousness. Anesthetics differ from analgesics in that analgesics such as aspirin, acetaminophen, ibuprofen, or morphine act to decrease pain, but not other sensations. Anesthetics can be broadly categorized into two general classes, local anesthetics and general anesthetics. These classes are independent as far as indication, chemical class, routes of administration, and toxicity, and thus will be considered separately. It will be noted when one compound within a class differs from the others. 

Poly(N-vinyl-pyrrolidone), or PNVP, is a biocompatible, water-soluble (JJ ) polymer that has previously been used as a synthetic blood plasma extender, as a component of soft contact lenses, and in a complex with iodine as the commercially available topical antiseptic Betadine ( ). It also forms a remarkable variety of chemically specific complexes with drugs and hormones such as the tetracyclines, phenothiazine antipsychotics, the antiepileptic drug phenytoin, procaine local anesthetics, and methyldopa antiparkinsonian drugs ( ). In its insoluble, chemically cross-linked form, PNVP has also been used as a concentrating agent for a variety of phenols and catechol compounds (22). 

There is considerable need to find medication that could be used to treat ciguatera specifically. Potentially useful drugs might include local anesthetics (Gillespie et al. 1986). These agents block the sodium channels by binding. 

Local anesthetics are used to locally anesthetize a wide range of specific body parts or areas to allow painless surgery. Local anesthetics are most commonly used for dental procedures and repair of lacerations. They can also be used to provide neural blockade for larger, more painful procedures. Sites of LA application include localized injection, peripheral nerve blocks as well as central nerve blockade. The only safe agents which can be utilized for intravenous regional anesthesia (Bier block) are lidocaine and prilocaine. Other typical indications are outlined in Table 64.1. 

An allergic reaction to specific agents is an obvious contraindication. Allergy to para-aminobenzoic acid (PABA) is a contraindication to use of ester local anesthetics due to the fact that PABA is a metabolic product of ester metabolism. Methylparaben is a common preservative chemically similar to PABA and likewise can cause an allergic reaction. Metabisulfite is a commonly used preservative that may also cause allergic reactions but more notably is neurotoxic when used intrathecally. Local anesthetics containing any preservative should not be used intrathecally. Ester local... 

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