For a 70 kg patient, what is the maximum number of vasopressor-containing carpules of 2% lidocaine?

• A. 6-7 Carpules
• B. 8-9 Carpules
• C. 10-11 Carpules
• D. 12-13 Carpules

Answer: (B)

The main idea is that the safety limit is the amount of epinephrine you inject, not the lidocaine amount, when a vasopressor is included. Each cartridge of lidocaine with vasopressor delivers a fixed dose of epinephrine depending on the concentration. With a common dental preparation at 1:80,000, a 1.8 mL carpule contains about 0.0125 mg/mL × 1.8 mL = 0.0225 mg of epinephrine. The maximum recommended epinephrine dose per dental visit for a healthy adult is around 0.2 mg. Dividing the limit by per-cartridge amount gives 0.2 mg / 0.0225 mg ≈ 8.9 cartridges, so eight to nine vasopressor-containing carpules is the practical maximum.

This demonstrates why the answer isn’t driven by lidocaine’s total mg per kg in this context—the epinephrine cap governs how many carpules you can safely use. If a different concentration were used (for example, 1:100,000), the per-carpule epinephrine would be smaller and the maximum would be around 11 carpules.