LOCAL ANESTHESIA IN DENTISTRY Clinical tips Articaine and Lidocaine: how their chemical properties can impact your clinical use Introduction Key items Local anesthetics such as lidocaine and • Reinjection articaine are the most commonly • Drug potency administered medications in dentistry. • Onset of action • Duration of anesthetic effect To appreciate the differences in these • Toxicity agents the chemical properties that • Use in patients younger than 4 differentiate them is important. years old • Use in geriatric patients The chemistry and pharmacology of a local • Complications anesthetic can give valuable information about which clinical effect you can expect Reinjection & Elimination half-life when you use them. The half-life of a drug is the amount of time that it will take the plasma concentration of a drug to be halved. Articaine contains an Articaine additional ester group that is quickly (and mostly) hydrolyzed by plasma esterases. This gives articaine an elimination half-life of approximately 20 minutes. The half-life of lidocaine is approximately 90 minutes. Thiophene ring Lidocaine is mostly hydrolyzed in the liver. The enzymes in the liver act slower than plasma enzymes. This makes reinjection of articaine safer, since the majority of the initial dose is metabolized after approximately half an hour, and the reinjected dose will not be added to the initial dose.1 Lidocaine Local Articaine Lidocaine anesthetic Elimination 20 minutes 90 minutes half-time Benzene ring Page 1 LOCAL ANESTHESIA IN DENTISTRY Clinical tips Drug potency & Lipid solubility protein bound agents are not reabsorbed into the central circulation as quickly and Lipid solubility affects the anesthetic therefore may have a lesser tendency potency. Potency represents the measure towards systemic toxicity. Articaine protein of a drug activity expressed in terms of the binding is higher than that of lidocaine.4 amount that is required in order to produce an effect of given intensity. The higher the Local Articaine Lidocaine lipid solubility, the greater the ability to anesthetic cross the lipid membrane of the epineuria, Protein 2 95% 65% which is 90% lipid. binding The lipid solubility of articaine is higher Metabolism & Systemic toxicity than lidocaine because it’s molecular structure contains a thiophene ring Metabolism of local anesthetics is whereas lidocaine contains a benzene ring. important, because the overall toxicity of a Thiophene is more lipid soluble than drug depends on a balance between its 3 benzene. rate of absorption into the bloodstream at the site of injection and its rate of removal Local Articaine Lidocaine from the blood. Approximately 70% of the anesthetic dose of injected lidocaine undergoes Lipid 49.5% 2.9% biotransformation in the liver of patients solubility with normal liver function. Onset of action & Dissociation constant Articaine differs from lidocaine in that it is (pKa) 90-95% metabolized in the blood and only 5 – 10% in the liver. Since articaine is not The dissociation constant (pKa) affects the as dependent as lidocaine for liver onset of action. A lower pKa means that metabolism, there is a higher degree of more uncharged base molecules are safety found with articaine in patients with present to diffuse through the nerve sheath hepatic disease. and thus the onset time is decreased. Articaine has a lower pKa than lidocaine.4 The major metabolic product of articaine is articainic acid. It is inactive as a local Local anesthetic and systemic toxicity has not Articaine Lidocaine 5 anesthetic been observed. This is important because an active metabolite may affect toxicity and pKa 7.8 7.9 may exert undesirable side effects. In comparison, lidocaine has an active Duration of anesthetic effect & Protein metabolite, xylidide, which is a local 3 binding anesthetic and potentially toxic. Local Local anesthetics are bound in different Articaine Lidocaine degrees of intensity to the proteins found in anesthetic 90-95% in 70% in the tissues including the nerves. This Metabolism parameter affects anesthesia duration. The the blood liver more highly protein bound an agent is, the longer it will stay and have an extended duration of action. In addition, highly Page 2 LOCAL ANESTHESIA IN DENTISTRY Clinical tips Use in pediatric patients be no reason to change the dosage in elderly patients.4 In order for a local anesthetic to become popular, it is important that it is useful in a wide range of situations. Local Articaine Lidocaine Lidocaine has been used for both adults anesthetic and children for more than five decades. Aging and physiologic Geriatric Articaine, however, is not indicated in changes can alter the drug patients children younger than 4 years of age. pharmacokinetics When used in pediatric dentistry, it is Local anesthetics & Complications important to remember that articaine is in a 4% solution and that the maximum dose A wide range of different complications can for children is the same as for adults: 7 occur during or after the injection of a local mg/kg (0.175 ml/kg). For simple anesthetic. They can be divided into local procedures the recommendation is 0.04 complications such as pain on injection, ml/kg and for complicated procedures the persistent anesthesia/paresthesia, trismus, recommendation is 0.07 ml/kg. It is hematoma, edema, facial nerve paralysis important to remember that when you and systemic complications such as administer a local anesthetic to children overdose and allergic reactions. with a small weight, the maximum dose 4 can easily be reached. Among these, we would like to highlight paresthesia, which is certainly not one of Local Articaine Lidocaine the most recurrent side effects, but many anesthetic discussions are still on going in regard to For children with a small the use of articaine in mandibular nerve Pediatric weight, the maximum dose block procedures and its increased risk of patients can easily be reached generating paresthesia. Use in geriatric patients Paresthesia can be defined as persistent anesthesia or altered sensation well Aging is associated with physiologic beyond the expected duration of changes that can alter the anesthesia. The symptoms are most pharmacokinetics of drugs. Age-related commonly associated with mechanical changes in pharmacokinetics affect drug trauma during surgical noxious stimuli. absorption, distribution, metabolism and During the administration of anesthesia for elimination. Increase in body mass, a mandibular block, the lingual or inferior decrease in lean body mass, total body alveolar neurovascular bundle can be water, changes in hepatic metabolism and traumatized by the sharp needle-tip, the renal elimination capacity in the elderly are movement of the needle, extraneural or of particular clinical significance. These intraneural hemorrhage from trauma to the changes should be taken into account blood vessels, or from neurotoxic effects of when choosing drug therapy for older the local anesthetics. patients to minimize adverse effects and maximize potential benefits. Haas and Lennon did a retrospective analysis of paresthesia after local Taking into account that articaine shows an anesthetic administration for nonsurgical age independent metabolism there should dental procedures over a 20-year period, Page 3 LOCAL ANESTHESIA IN DENTISTRY Clinical tips from 1973 – 1993, in 1995. The analysis direction of the needle at the approximate revealed a higher than expected frequency depth of the lingual nerve. The sharp of paresthesia with articaine based on the needle tip may lacerate the lingual nerve number of cartridges used. There were no and/or artery on the initial or subsequent significant differences found with respect to path. Another possible explanation might patient age, patient gender or needle be that during a subsequent injection for gauge.6 the inferior alveolar nerve block, the needle might traumatize the more superficial Subsequently in JADA, February 2001, lingual nerve but without the “electric Malamed, ET. Al. reported on three shock” sensation because the nerve is identical single-dose, randomized, double usually anesthetized on the initial attempt. blind, parallel-group, active-controlled The cause of paresthesia may also be a multicenter studies that were conducted to combination of neurotoxicity of the local compare the safety and efficacy of anesthetic and trauma to the nerve. articaine (4% with epinephrine 1:100,000) with that of lidocaine (2% with epinephrine Local Articaine Lidocaine 1:100,000). A total of 1,325 subjects anesthetic participated in these studies, 882 of whom Can be associated with the received articaine 4% with epinephrine use of any local anesthetic. 1:100,000 and 443 of whom received Controversial conclusions lidocaine 2% with epinephrine 1:100,000. Paresthesia still exist in regard to The overall incidence of adverse events in articaine and its increased the combined studies was 22% for the risks associated to articaine group and 20% for the lidocaine paresthesia group. The most frequently reported adverse events in the articaine group, Conclusion excluding post procedural dental pain, were headache (4%), facial edema, A range of local anesthetic drugs has been infection, gingivitis and paresthesia (1% used in dentistry. Although lidocaine each). The incidence of these events was continues to be used more than articaine in similar to that reported for subjects who the US, many dentists have begun using received lidocaine. articaine as a more definitive means of achieving profound anesthesia. The adverse events most frequently reported as related to articaine use were Many dentists who continue to use paresthesia (0.9 percent), hypoesthesia lidocaine refer to the lower cost of (0.7%), headache (0.55%), infection lidocaine. Due to the fact that articaine is a 7 (0.45%), and rash and pain (0.3% each). 4% solution and lidocaine is a 2% solution, a dentist would theoretically only need to An interesting finding in the Haas and use one-half the volume of articaine to get Lennon analysis is the different frequency the same level of anesthesia, which makes between paresthesia of the lingual nerve the cost of the two anesthetics very and the inferior alveolar nerve.