Local anesthetics ideal

An important property of the ideal local anesthetic is low systemic toxicity at an effective concentration. Onset of action should be quick, and duration of action should be sufficient to allow time for the surgical procedure. The local anesthetic should be soluble in water and stable in solution. It should not deteriorate by the heat of sterilization, and it should be effective both when injected into tissue and when applied topically to mucous membranes. Its effects should be completely reversible. 

Although the characteristics of an ideal local anesthetic are easily identifiable, synthesis of a compound possessing all these properties has not been accomplished. The compounds discussed in the following sections fall short of the ideal in at least one aspect. However, the judicious choice of a particular agent for a particular need will permit the practitioner to employ local anesthesia effectively and safely. 

Pharmacological Profile. The profile of the ideal local anesthetic agent depends largely on the type and length of the surgical procedure for which it is applied. Procedures could include neuraxial (spinal and epidural) anesthesia, nerve and plexus blocks, or field blocks (local infiltration). In general, tine ideal agent should have a short onset of anesthesia and be useful for multiple indications such as infiltration, nerve blocks. 

Practitioners should record the event in the patient s chart and avoid using the same anesthetic on subsequent patient visits. Because there is apparently little cross-sensitivity between classes of local anesthetics, practitioners can usually change from proparacaine to an ester of PABA, or vice versa, with little risk of local allergy. Unfortunately, no topical anesthetics approved for ocular use have an amide linkage. Such anesthetics, because of their extremely low allergenic potential, would serve as ideal topical ocular anesthetics. 

Figure 13-9. Idealized local anesthetic-receptor interactions. (Modified from Buchi et al., 1966 Buchi and Perlia, 1960.)...

An ideal local anesthetic should produce reversible blockade of sensory nerve fibers with a minimal effect on the motor fibers. It also should possess a rapid onset and have a sufficient duration of action for the completion of major surgical procedures without any systemic toxicity. 

Because of its ability to block pain, cocaine became widely used as a local anesthetic to deaden nerves during various medical procedures, but it was not an ideal anesthetic owing to its undesired side effects. For example, in eye surgery it produces mydriasis, or dilation of the pupil It also has powerful addictive properties and exhibits dangerous effects on the central nervous system. Medicinal chemists thus began a search for substances related to cocaine that would retain its valuable anesthetic properties but would not produce its side effects. 

Lidocaines rapid onset of action makes it an ideal choice for peripheral neural blockade that will function as the sole surgical anesthetic. Its relatively safe cardiotoxicity profile also increases its attractiveness when compared to other local anesthetics such as bupivacaine or ropivacaine. It is also widely available commercially in generic form for low cost. A 20-mL vial of hdocaine 2% with epinephrine 1 200k costs between 4 and 6 [1,2]. 

Pain and hyperthermia at the injection site can be reduced by pre-administration neural blockade, and administration during general anesthesia. Ideally, Adlea may he applied to patients receiving anesthesia and post-operative analgesia with epidural and peripheral neural blockade catheters. Residual pain may be controlled with local application of ice packs, local anesthetic infiltration, and oral acetaminophen. 

Musculoskeletal In an up-to-date review of the available basic science English literature, the authors describe a consistent finding that local anesthetics have toxic effects on articular chondrocytes and conclude that intra-articular local anesthetics should be used with caution [16 ]. However, the authors point out that comparing the results of multiple models (ex vivo and in vitro), different cell lines from different species and heterogeneous treatment protocols is fraught with difficulties. They suggest that the ideal in vitro or in vivo model is yet to be found to assess the chondrotoxic effects of intra-articular local anesthetic administration. 

Chemical blepharoplasty and cheiloplasty are ideally carried out with Lip Eyelid formula its action is more gradual than that of Baker-Gordon or Litton phenol, and it can be applied locally without any anesthetic since the pain only lasts 12-15 seconds. 

---