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Dose Calculations Made Routine Chapter: Dose Calculations and Maximum Recommended Doses
🖨 Print or save as PDF Updated 2026-10-20
mg per cartridge (mg/mL = % × 10) Solution mg/mL mg per 1.8 mL mg per 1.7 mL MRD (commonly taught, Malamed) Lidocaine 2% 20 36 34 7.0 mg/kg, max 500 mg (older texts 4.4 mg/kg, 300 mg) Mepivacaine 3% 30 54 51 6.6 mg/kg, max 400 mg Mepivacaine 2% 20 36 34 6.6 mg/kg, max 400 mg Articaine 4% 40 72 68 7.0 mg/kg; no U.S. absolute maximum listed Prilocaine 4% 40 72 68 8.0 mg/kg, max 600 mg Bupivacaine 0.5% 5 9 8.5 Max 90 mg (Canada: 2.0 mg/kg)
U.S. cartridges are labeled 1.7 or 1.8 mL depending on the product; check which volume your course and exam use. Vasoconstrictor limits Ratio mg per 1.8 mL Healthy adult (0.2 mg epinephrine; 1.0 mg levonordefrin) Significant cardiovascular disease (0.04 mg epinephrine) Epinephrine 1:50,000 0.036 About 5.5 cartridges About 1 cartridge Epinephrine 1:100,000 0.018 About 11 cartridges About 2 cartridges Epinephrine 1:200,000 0.009 About 22 cartridges (drug limit is reached first) About 4 cartridges Levonordefrin 1:20,000 0.09 About 11 cartridges Avoid or keep to the minimum
The 0.04 mg cardiac figure is a commonly taught guideline, not a hard ceiling: aspirate, inject slowly and monitor vital signs. Four-step method 1) Convert weight: kg = lb ÷ 2.2. 2) Maximum mg = MRD (mg/kg) × kg, then cap at the absolute maximum. 3) Cartridges = maximum mg ÷ mg per cartridge; round DOWN. 4) Check the vasoconstrictor limit and use the lower of the two answers. When two different drugs are used, their percentages of each maximum add up (e.g., half the lidocaine maximum leaves half the mepivacaine maximum). Worked examples (1.8-mL cartridges) 60-kg adult, lidocaine 2% with 1:100,000: 7.0 × 60 = 420 mg → 420 ÷ 36 = 11.7; epinephrine 0.2 ÷ 0.018 = 11.1 → about 11 cartridges. 110-lb (50-kg) adult, mepivacaine 3%: 6.6 × 50 = 330 mg → 330 ÷ 54 = 6.1 → 6 cartridges. 30-kg child, mepivacaine 3%: 6.6 × 30 = 198 mg → 198 ÷ 54 = 3.7 → 3 cartridges. 90-kg adult, prilocaine 4%: 8.0 × 90 = 720 mg, capped at 600 mg → 600 ÷ 72 = 8.3 → 8 cartridges. Bupivacaine 0.5%: 90 mg ÷ 9 mg = 10 cartridges is the absolute ceiling; a smaller patient gets less if your course uses a mg/kg limit. ⚠️ Common traps Forgetting the absolute maximum in a large patient (the 90-kg prilocaine case). Rounding cartridges up: always round down. Ignoring the vasoconstrictor limit, which can be lower than the drug limit (1:50,000 and 1:100,000). Mixing 1.7-mL and 1.8-mL values in the same problem. Mini-quiz Pick an answer to see right away whether it is correct and why.
How many mg of drug are in one 1.8-mL cartridge of 4% articaine?
A. 72 mg B. 36 mg C. 68 mg D. 40 mg
A 50-kg patient receives mepivacaine 3% plain (MRD 6.6 mg/kg). What is the maximum number of 1.8-mL cartridges?
A. 4 B. 6 C. 7 D. 8
A patient with significant cardiovascular disease is limited to 0.04 mg epinephrine. How many 1.8-mL cartridges of 1:100,000 is that?
A. About 1 B. About 2 C. About 4 D. About 11
A 90-kg patient gets prilocaine 4% (8.0 mg/kg, max 600 mg). Maximum 1.8-mL cartridges?
A. 10 B. 9 C. 6 D. 8
A 70-kg adult receives lidocaine 2% with 1:50,000 epinephrine. Which limit is reached first?
A. Lidocaine, at about 13 cartridges B. Both at exactly the same point C. Epinephrine, at about 5 cartridges D. Neither; there is no limit for healthy adults
0 of 5 answered
Answer key: 1 A · 2 B · 3 B · 4 D · 5 C
