Plain choice when a vasoconstrictor should be avoided; AAPD pediatric 4.4 mg/kg
Mepivacaine 2% with levonordefrin 1:20,000
20
34
6.6
400 mg
Levonordefrin: avoid with tricyclic antidepressants
Articaine 4% with epinephrine 1:100,000 or 1:200,000
40
68
7.0
None listed in U.S. labeling (500 mg commonly used as a ceiling)
Thiophene ring and ester side chain: mostly broken down in plasma; label not for children under 4
Prilocaine 4% plain or with epinephrine 1:200,000
40
68
8.0
600 mg
Methemoglobinemia risk (o-toluidine metabolite)
Bupivacaine 0.5% with epinephrine 1:200,000
5
8.5
1.3 (newer Malamed editions: 2.0)
90 mg
Long-acting; useful for long surgery and postoperative pain
mg per mL = % × 10. mg per cartridge = mg/mL × mL. (Some texts still compute with 1.8 mL: 2% lidocaine = 36 mg.)
Maximum dose (mg) = mg/kg × weight (kg), never above the absolute maximum. Cartridges = maximum mg ÷ mg per cartridge.
Vasoconstrictor content
Ratio
mg per mL
mg per 1.7-mL cartridge
Healthy-adult limit
Cardiac-patient limit (commonly taught)
Epinephrine 1:50,000
0.02
0.034
0.2 mg ≈ 5.9 cartridges
0.04 mg ≈ 1.2 cartridges
Epinephrine 1:100,000
0.01
0.017
0.2 mg ≈ 11.8 cartridges
0.04 mg ≈ 2.4 cartridges (about 2)
Epinephrine 1:200,000
0.005
0.0085
0.2 mg ≈ 23.5 cartridges (the anesthetic limit is reached first)
0.04 mg ≈ 4.7 cartridges (about 4)
Levonordefrin 1:20,000
0.05
0.085
1.0 mg ≈ 11.8 cartridges
0.2 mg ≈ 2.4 cartridges
1 : 100,000 means 1 g in 100,000 mL = 1,000 mg ÷ 100,000 mL = 0.01 mg/mL.
The 0.04 mg cardiac limit is a commonly taught (Malamed) guideline for patients with significant cardiovascular disease, not a hard evidence-based ceiling; aspirate, inject slowly and monitor vitals.
Worked examples
Healthy 70-kg adult, 2% lidocaine 1:100,000: 7.0 × 70 = 490 mg (under 500) → 490 ÷ 34 = 14.4 cartridges by lidocaine, but epinephrine 0.2 ÷ 0.017 = 11.8 → the epinephrine limit applies: about 11 cartridges.
Defer elective care (and avoid epinephrine) with: MI or stroke within the last 6 months (commonly taught), unstable angina, uncontrolled hypertension (≥ 180/110 mmHg), uncontrolled arrhythmias, uncontrolled hyperthyroidism, recent cocaine or methamphetamine use (commonly taught: no epinephrine within 24 h of cocaine).
Interactions: nonselective β-blockers (propranolol) → hypertension with reflex bradycardia; tricyclic antidepressants → exaggerated pressor response (limit epinephrine, avoid levonordefrin); general anesthetics such as halothane → arrhythmias.
Avoid epinephrine-impregnated retraction cord in cardiovascular patients.
Toxicity and adverse reactions
Overdose is CNS excitation then depression: circumoral numbness, tingling, tinnitus, dizziness, slurred speech, muscle twitching → seizures → CNS and respiratory depression.
Management: stop injecting, position, oxygen, monitor, basic life support; a seizure lasting more than 5 minutes is treated with a benzodiazepine (midazolam); call EMS.
Methemoglobinemia (prilocaine, topical benzocaine): gray-blue cyanosis that does not improve with oxygen; treat with IV methylene blue.
Esters (benzocaine, tetracaine, procaine) are hydrolyzed by plasma pseudocholinesterase and form PABA, the usual cause of true LA allergy. Allergy to amides is very rare; sulfite preservative (in vasoconstrictor-containing cartridges) can trigger reactions in sulfite-sensitive asthmatics.
Lower pKa → more uncharged base at tissue pH → faster onset. Inflamed, acidic tissue traps the drug in its charged form and weakens the block.
⚠️ Common traps
Using 7.0 mg/kg for a child when the question names the AAPD table (4.4 mg/kg for lidocaine and mepivacaine).
Forgetting that epinephrine, not the anesthetic, limits 1:100,000 lidocaine in many healthy adults.
Mixing up 1:100,000 (0.01 mg/mL) with 1:1,000 (1 mg/mL, the anaphylaxis strength).
Calculating cartridges from the mg/kg value without capping at the absolute maximum.
Treating methemoglobinemia with oxygen alone.
Mini-quiz
Pick an answer to see right away whether it is correct and why.
How many milligrams of lidocaine are in one 1.7-mL cartridge of 2% lidocaine?
A patient with stable angina may receive the commonly taught cardiac maximum of 0.04 mg epinephrine. About how many 1.7-mL cartridges of 1:100,000 epinephrine is that?
Which local anesthetic is most associated with methemoglobinemia?
A 25-kg child is to receive 4% articaine with epinephrine (maximum 7.0 mg/kg). About how many 1.7-mL cartridges is the maximum?
Which is typically the earliest sign of local anesthetic overdose?
0 of 5 answered
Answer key: 1 C · 2 B · 3 A · 4 B · 5 A
Dental School Map · Original study material, written and checked by our team; always confirm clinical decisions against current guidelines.
