Local Anesthetic Agents + MRD PDF

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lecture notes on Local Anesthetic Agents + MRD...

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Local Anesthetic Types ESTERS 

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Names of ester drugs have one “i”: procaine, propoxycaine, cocaine, etc. (names of amide drugs contain two “i"s, e.g., lidocaine). + Novocaine is the brand name for procaine (generic name) and is no longer available in North America. Esters are biotransformed in the blood. Esters are more likely to cause allergic reactions compared to amides. Patients are not allergic to the ester drug itself, but to the byproduct of the drug called para-aminobenzoic acid (PABA). PABA is formed when the drug is metabolized in the blood plasma by plasma pseudocholinesterase. Esters are no longer available as injectable local anesthetics, but they are used as topical anesthetics (e.g., benzocaine topical).

Amides vs esters

AMIDES   

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Names of amide drugs have two ”i”s: lidocaine, mepivacaine, articaine, prilocaine, bupivacaine, etc. Amide drugs are biotransformed in the liver (exception: articaine, which is biotransformed ~90-95% in the blood and ~5-10% in the liver). Lidocaine + Brand name: Xylocaine. + Metabolized in the liver. + Pregnancy category B - this is the safer category compared to category C. Only lidocaine and prilocaine are category B drugs among local anesthetics (refer to the pregnancy category of drugs at the end of the section). + MRD: 500 mg/appointment, or 3.2 mg/lb (7 mg/kg). + 2% concentration, 1:50,000 epinephrine: 60 mins (nerve block) pulpal, 35 hrs soft tissue anesthesia. + 2% concentration, 1:100,000 epinephrine: 60 mins (nerve block) pulpal, 3-5 hrs soft tissue anesthesia. + Half-life: 1.9 hrs. + Represents the “gold standard” drug against which other drugs are compared to. Mepivacaine + Brand name: Carbocaine. + Metabolized in the liver. + Least vasodilating drug among those used in dentistry. + Pregnancy category C. + MRD: 400 mg/appointment, or 3.0 mg/lb (6.6 mg/kg). + 2% concentration, 1:20,000 levonordefrin: 60 mins (nerve block) pulpal, 3-5 hrs soft tissue anesthesia. + 3% concentration, plain: 20 (infiltration)-40 (nerve block) mins pulpal, 2-3 hrs soft tissue anesthesia. + Half-life: 1.9 hrs. + Plain solution is recommended when vasoconstrictors are contraindicated or if the dental procedures only require 30 minutes of pulpal anesthesia. + Often used with geriatric, pediatric, and mentally-challenged patients. Prilocaine + Brand name: Citanest (called Citanest Forte if the solution contains epinephrine). + Metabolized in the liver, lungs, and kidneys. + Pregnancy category B. + MRD: 600 mg/appointment, or 4.0 mg/lb (8 mg/kg). + 4% concentration, 1:200,000 epinephrine: 60-90 mins (nerve block) pulpal, 3-5 hrs soft tissue anesthesia. + 4% concentration, plain: + Nerve block: 40-60 mins pulpal, 2-4 hrs soft tissue anesthesia. + Infiltration: 10-15 mins pulpal, 1 ½-2 hrs soft tissue anesthesia. + Half-life: 1.6 hrs.

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+ Methemoglobins (abnormal hemoglobin with reduced oxygen binding capacity) can form as a result of prilocaine metabolism. Signs and symptoms of methemoglobinemia include cyanosis (can cause observable pale to bluish lips, mucous membranes, nails, etc.) and respiratory distress. + For this reason, prilocaine is contraindicated with idiopathic or congenital methemoglobinemia. + Reported to cause higher incidences of paresthesia with the IA nerve block. Articaine + Brand name: Septocaine. + Metabolized in the liver and blood plasma. + Only amide anesthetic that contains an ester group. + Pregnancy category C. + MRD: No absolute MRD. 3.2 mg/lb (7 mg/kg). + 4% concentration, 1:100,000 epinephrine: 60-75 mins (nerve block) pulpal, 3-6 hrs soft tissue anesthesia. + 4% concentration, 1:200,000 epinephrine: 45-60 mins (nerve block) pulpal, 2-5 hrs soft tissue anesthesia. + Half-life: 0.5 hrs. + Biotransformed faster than other amide local anesthetics because of its dual metabolism (90% in the blood and 5-10% in the liver). + Reported to diffuse through soft and hard tissues more reliably, therefore increasing the success of the anesthesia. + Reported to have higher incidences of paresthesia. Bupivacaine + Brand name: Marcaine. + Metabolized in the liver. + Pregnancy category C. + MRD: 90 mg/appointment. No mg/kg (mg/lb) in the United States. 0.9 mg/lb (2.0 mg/kg) in Canada. + 0.5% concentration, 1:200,000 epinephrine: 90-180 mins (nerve block) pulpal, 4-9 hrs soft tissue anesthesia. + Half-life: 2.7 hrs. + 4 times more potent and toxic compared to lidocaine and mepivacaine. It is only used for: + Longer procedures (e.g., periodontal surgery, implant surgery, etc.). + Management of postoperative pain. Can be injected shortly before the patient leaves the office to prolong anesthetic effects.

NOTE: FDA pregnancy categories of drugs  

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Category A: best, failed to demonstrate a risk to the human fetus in the first trimester of pregnancy. Category B: animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women. + Amoxicillin, lidocaine, prilocaine, etc. Category C: animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans. + Acetaminophen, rifampin (anti-TB), mepivacaine, septocaine, etc.

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Category D: positive evidence of human fetal risk. Potential benefits may warrant use of the drug in pregnant women despite potential risks. + Aspirin, phenytoin (anti-seizure), tetracycline (antibacterial), etc. Category X: studies in animals or humans have demonstrated fetal abnormalities. + Temazepam (anti-anxiety), etc.

Calculating Local Anesthetic Drug Dose AMOUNT OF LOCAL ANESTHETICS IN A CARTRIDGE 

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The amount of local anesthesia is represented as a percentage (%) on dental cartridges. The number in % indicates the grams of drug per 100 ml of solution. + e.g., 2% = 2 g/100 ml; 3% = 3 g/100 ml; 4% = 4 g/100 ml Amount of g should be converted into mg in order to match the ml unit. + 1 g = 1000 mg + 0.5% = 0.5 g/100ml = 500 mg/100 ml = 5 mg/ml + 2% = 2 g/100ml = 2000 mg/100 ml = 20 mg/ml + 3% = 3 g/100ml = 3000 mg/100 ml = 30 mg/ml + 4% = 4 g/100ml = 4000 mg/100 ml = 40 mg/ml In order to calculate the amount of local anesthetic in a cartridge, multiply the drug per ml by 1.8 (or 1.7 if the cartridge contains 1.7 ml of solution). + 0.5% drug: 5 mg/ml x 1.8 ml = 9 mg; 0.5% drug: 5 mg/ml x 1.7 ml = 8.5 mg + 2% drug: 20 mg/ml x 1.8 ml = 36 mg; 2% drug: 20 mg/ml x 1.7 ml = 34 mg + 3% drug: 30 mg/ml x 1.8 ml = 54 mg; 3% drug: 30 mg/ml x 1.7 ml = 51 mg + 4% drug: 40 mg/ml x 1.8 ml = 72 mg; 4% drug: 40 mg/ml x 1.7 ml = 68 mg + To simplify the calculation, multiply 18 (or 17 depending on the cartridge) by the number in front of the %. e.g., 18 x 0.5 = 9 (mg), 18 x 2 = 36 (mg), etc. This will give you the amount of anesthetic in a cartridge. If the cartridge was not used in full, multiply the total amount of solution in a full cartridge by the amount used. + e.g., half of 2% lidocaine cartridge used: 36 mg x 1/2 = 18 mg; quarter of 2% lidocaine cartridge used: 36 mg x 1/4 = 9 mg. If multiple cartridges were used, multiply the amount of local anesthetic per cartridge by the number of cartridges used. + e.g., 3 cartridges of 2% lidocaine used: 36 mg x 3 = 108 mg; 4 cartridges of 2% lidocaine used: 36 mg x 4 = 144 mg.

ADULT LOCAL ANESTHETIC MRD 

If the patient is 150 pounds or heavier, use the absolute highest MRD set by the manufacturer (e.g., patient weight 180 lbs, MRD for mepivacaine 1:20,000 is 400 mg/appointment)

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If the patient is lighter than 150 lbs, calculate the MRD based on the patient’s weight (e.g., if the patient weighs 100 lbs, the MRD for mepivacaine 1:20,000 is 300 mg/appointment, 3 mg/lb x 100 lb) Lidocaine: 500 mg/appointment, or 3.2 mg/lb (7 mg/kg) Mepivacaine: 400 mg/appointment, or 3.0 mg/lb (6.6 mg/kg) Prilocaine: 600 mg/appointment, or 4.0 mg/lb (8 mg/kg) Articaine: No absolute MRD per appointment, or 3.2 mg/lb (7 mg/kg) Bupivacaine: 90 mg/appointment. No mg/kg or mg/lb in the United States. 0.9 mg/lb (2.0 mg/kg) in Canada.

PEDIATRIC LOCAL ANESTHETIC MRD    

A pediatric patient refers to patients under the age 18. Multiply the child’s body weight by the MRD/lbs (or kg) if the child is below 150 lbs. e.g., 50 lbs child, mepivacaine plain (MRD 2.0 mg/lb), 2.0 mg/lb x 50 lb = 100 mg. The most common type of overdose in dentistry is related to over administration of local anesthetic in children. MRD defined by the American Academy of Pediatric Dentistry guidelines: + Lidocaine: 300 mg/appointment or 2.0 mg/lb (4.4 mg/kg). + Mepivacaine: 300 mg/appointment or 2.0 mg/lb (4.4 mg/kg). + Articaine: 500 mg/appointment or 3.2 mg/lb (7.0 mg/kg). + Prilocaine: 400 mg/appointment or 2.7 mg/lb (6.0 mg/kg). + Bupivacaine: 90 mg/appointment or 0.6 mg/lb (1.3 mg/kg).

CALCULATING LOCAL ANESTHETIC MRD IN CARTRIDGES 

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Step 1: find the MRD specified by the manufacturer in mg according to the local anesthetic and the patient’s weight. + If the patient is over 150 lbs, apply the absolute highest MRD set by the drug manufacturer. e.g., lidocaine with epinephrine MRD is 500 mg/appointment. + If the patient is under 150 lbs, calculate the MRD by multiplying the patient’s weight and the MRD per lb. e.g., 100 lbs patient, 100 lb x 3.2 mg/lb = 320 mg. Step 2: find the amount of local anesthetic in a cartridge (there is either 1.7 ml or 1.8 ml). e.g., 1 cartridge - assuming the cartridge is listed as 1.8 ml - of lidocaine 2% has 36 mg of local anesthetic (regardless of whether the cartridge contains epinephrine or not). Step 3: divide step 1 by step 2 (MRD / amount of local anesthetic in 1 cartridge). + e.g., If patient is over 150 lbs, use the absolute MRD (MRD listed on the drug insert packet). e.g., 500 mg/36 mg = 13.8 cartridges. + e.g., If patient is under 150 lbs, use the MRD by weight. (e.g., 320 mg/36 mg = 8.9 cartridges). When two and more drugs are used, the total dose of both local anesthetics should not exceed the lowest MRD of all the drugs (referred to as the limiting factor). + e.g., prilocaine 200 mg was administered and the clinician would like to administer lidocaine. How much lidocaine can be given? If the patient is over

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150 lbs, the MRD for prilocaine is 600 mg/appointment while the MRD for lidocaine is 500 mg/appointment. If the patient is under 150 lbs (e.g., 100 lbs), the MRD for prilocaine is 400 mg (100 lb x 4.0 mg/lb = 400 mg) while the MRD for lidocaine is 320 mg (100 lb x 3.2 mg/lb = 320 mg). Regardless of the patient’s weight, the lower MRD between lidocaine and prilocaine becomes the limiting factor. In this case, lidocaine has a lower MRD with 500 or 320 mg/appointment. Since 200 mg was already given, 300 (or 120) mg more of local anesthetic can be administered....