Influence of ph Most local anesthetics are weak bases.

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1 Local anesthetics The agent must depress nerve conduction. The agent must have both lipophilic and hydrophilic properties to be effective by parenteral injection. Structure-activity relationships The typical local anaesthetics molecule can be divided into three parts: an aromatic group, an intermediate chain, a secondary or tertiary amino terminus. Influence of ph Most local anesthetics are weak bases. Mechanism of action Both the generation and the conduction of nerve action potentials are inhibited. Pharmacologic effects Local anesthetics are not selective. Except local action, they may affect: the cardiovascular and central nervous systems, any organ dependent on nervous or muscular activity Pharmacologic effects:- central nervous system Initial signs and symptoms of a toxic effect consist of a feeling of lightheadedness and dizziness Further on develop: visual and auditory disturbances, apprehension, disorientation, localized involuntary muscular activity. slurred speech, drowsiness, unconsciousness Pharmacologic effects- cardiovascular system: Local anesthetics depress myocardial contractility in a dose-dependent manner. Toxic blood concentrations may cause arteriolar dilation and profound hypotension. Local anesthetics listed in decreasing potential for causing vasodilation, include bupivacaine, procaine, lidocaine, prilocaine, mepivacaine, and cocaine. Vasoconstrictor effects: Vasoconstrictors are often added to local anesthetic solutions to impede systemic absorption of the anesthetic agent. The duration of local anesthesia may be prolonged several times, and even the success rate and intensity of nerve block may be improved. Systemic toxicity may be reduced because less anesthetic may be needed, and drug metabolism is more likely to keep pace with drug absorption.

2 For example, a 3% plain mepivacaine solution would be 50% more toxic than an equal volume of 2% mepivacaine with levonordefrin. Absorption The rate of absorption depends on several factors, including: the dosage pharmacologic profile the presence of vasoconstrictor agent the nature of the administration site. Drugs with potent vasodilating properties, such as procaine and lidocaine, may enhance their own uptake. Inclusion of epinephrine or another vasoconstrictor is especially important in these instances. Drugs that are not strong vasodilators, such as mepivacaine and prilocaine, do not require as much vasoconstrictor. Uptake may be minimized, however by using local anesthetics preparated in the form of an ointment or gel instead of an aqueous spray. Adverse effects- systemic toxicity Most toxic effects of a serious nature are releted to excessive blood concentrations caused by inadvertent intravascular injection or the administration of large quantities of drug. Convulsions, respiratory arrest, and cardiovascular collapse represent the greatest hazards to health. Such reactions can usually be prevented by observing three precautions: 1.administer the smallest dose that will provide effective anesthesia; 2.use proper injection techniques, including aspiration 3. use a vasoconstrictor-containing solution when not contraindicated by patient history or operative need. Use during pregnancy Local anesthetics are generally regarded as safe for use throughout pregnancy. The Food and Drug Administration has classified lidocaine and prilocaine in pregnancy risk category B and articaine, mepivacaine, and bupivacaine in category C. Surface application Tetracaine and lidocaine are useful topical agents as single agents, whereas mepivacaine, prilocaine, and procaine are not. Benzocaine, ineffective parenterally, is well adapted for surface anesthesia because of its slow systemic absorption and relative safety. Spinal anesthesia Tetracaine, lidocaine, and bupivacaine are most commonly used for spinal anesthesia in the United States, but numerous other agents are also used.

3 Treatment of cardiac arrhythmias Lidocaine, procainamide have establised roles in the therapeutic management of cardiac arrhythmias. Uses in dentistry Maximum doses Preparation contents--- proprietary name--- maximum dose 2% Lidocaine hydrochloride; 1:100,000 epinephrine----xylocaine with epinephrine mg/kg mg 2% Lidocaine----Xylocaine mg/kg mg 2% Mepivacaine hydrochloride; 1:20,000 levonordefrin---scandonest 2% mg/kg mg 3% Mepivacaine hydrochloride---carbocaine mg/kg mg 4% Prilocaine hydrochloride; 1:200,000 epinephrine----citanest Forte mg/kg mg 4% Prilocaine hydrochloride----citanest mg/kg mg 0.5% Bupivacaine hydrochloride; 1:200,000 epinephrine--- Marcaine with epinephrine mg 4%Articaine hydrochloride; 1:1000,000 epinephrine---septocaine mg\kg Drug selection A) 2% lidocaine hydrochloride with 1:100,00 epinephrine remains a standard dental anesthetic for routine use. B) Mepivacaine is generally equivalent to lidocaine in its pharmacologic profile. Two distinctive features of mepivacaine are its topical ineffectiveness and its use as a 3% solution without a vasoconstrictor. C) Prilocaine is a less potent and less toxic alternative to lidocaine. Like mepivacaine, it is not used topically as a single agent but is effective for dental application without epinephrine. D) Articaine is the only thiophene-based amide local anesthetic. E) Bupivacaine is slightly slower in onset than the other amides but is equally efficacious and has a much longer duration of action, making it well suited for providing post-operative pain relief in oral surgery. F) Soft tissue anesthesia is comparatively brief after maxillary infiltration with 3% mepivacaine or 4% prilocaine (both without vasoconstrictor). Because the period of pulpal anesthesia is often 20% to 25% that of soft tissue anesthesia, the limited maxillary duration of these agents is sometimes disadvantageous. For instance, 4% prilocain, has a shorter duration by one fifth of the time as compared with 2% lidocaine with epinephrine. Drug selection in children Systemic toxicity should limit the pedodontic use of local anesthetics without vasoconstrictors.

4 Not doing so would result in more total anesthetic drug being administered. Lidocaine with 1:50,000 epinephrine can be advantageous when surgical hemostasis is desired. Articaine with epinephrine may be considered for situations in which the drug s short metabolic half-life and possible increased efficacy may prove advantageous. Bupivacaine with epinephrine would be good choice for nerve block if a truly extended effect is desired. Lidocaine hydrochloride - it is several times more potent and toxic than procaine and provides more prompt, more extensive, and longer lasting local anesthesia, - the aministration of 2% lidocaine hydrochloride with 1:100,00 epinephrine is most suitable for routine dental use, - although 2% lidocaine with vasoconstrictor provides satisfactory dental anesthesia in normal cirumstances, it has sometimes proved ineffective in rendering extremely sensitive teeth completely pain free, - a concentrated solution of 5% lidocaine with 1:80,000 epinephrine has been shown to produce effective anesthesia in most instances when conventional local anesthetic preparations have failed, - lidocaine is the only amide marketed as a single agent for topical anesthesia in dentistry, Mepivacaine hydrochloride - similar in many respects to lidocaine, mepivacaine hydrochloride is marketed in a 2% concentration with 1:20,00 levonordefrin and as a 3% solution without vasoconstrictor Prilocaine hydrochloride - somewhat less potent than lidocaine, prilocaine hydrochloride is marketed as a 4% solution with and without 1:200,000 epinephrine, - because the systemic toxicity of prilocaine is approximately half that of lidocaine, toxic effects on a milliliter basis are essentially equal, Articaine hydrochloride - marketed in the United States in a 4% concentration with 1:100,000 epinephrine (and with 1:200,000 epinephrine in Canada), articaine has become a popular agent for routine use in dentistry, - the high concentration of the agent may increase the danger of intravascular injection and the risk of nerve damage in the immediate area of injection, Bupivacaine hydrochloride - is approximately four times as potent and as toxic as mepivacaine; it also has a slower onset of action,

5 - for dentistry, 0.5% bupivacaine hydrochloride is available with 1:200,000 epinephrine, - bupivacaine with epinephrine given for nerve block produces operative anesthesia several times longer than that afforded by other drugs. - bupivacaine is less effective and shoter acting than lidocaine for pulpal anesthesia after maxillary supraperiosteal injection. Agents limited to surface application Topical anesthetics are used in the oral cavity for a variety of purposes. Formulations marketed as pressurized sprays produce widespread surface anastheshia apprioprate for making impressions or intraoral radiographs. Topical liquids, which avoid the possibility of aerosol inspiration may also be used for anesthetic coverage of large surface areas. Nonaqueous topical preparations are suitable for most other procedures. Benzocaine - poorly soluble in aqueous fluid, benzocaine tends to remain at the application and is not readily absorbed of into the systemic circulation, - is especially useful for anesthesia of large surface areas within the oral cavity, Tetracaine hydrochloride - it is no longer available for injection in dentistry - is one of the most effective topical anesthetics, but the drug s toxic potential after surface application should dictate caution in its use. - for surface application it is marketed as a 2% hydrochloride salt in combination with 14% benzocaine and 2% butamben in an aerosol spray, solution, gel, and ointment (Cetacaine). Lidocaine/ prilocaine - marketed under the name of EMLA, a mixture of 2.5% lidocaine and 2.5% prilocaine is available in the form of a cream for topical anesthesia of the skin, - when placed under an occlusive dressing for 1 hour, EMLA obtunds the pain of venipuncture and finds special use in young children and other patients intolerant of needle insertion, - although this formulation is not intendend for topical anesthesia of the oral cavity (and tastes bad and has poor physical characteristics for intraoral use), it may be better in relieving pain of oral tissues. - an intraoral preparation with the same active ingredients of EMLA has been marketed with the name of Oraqix- it provides local anesthesia for periodontal scaling and root planing.