A 120-pound patient has received 2 cartridges of 2% mepivacaine, 1:20,000 and does not remain adequately numb during the procedure. How many additional cartridges of 2% lidocaine, 1:100,000 epinephrine may the patient receive before reaching the MRD?
A) 6
B) 9
C) 11
D) 13

Question

Quizplus · Accepted Answer

The maximum recommended dose (MRD) for lidocaine with epinephrine in a healthy adult is 7 mg/kg. For a 120-pound patient, which is approximately 54.5 kg (120 lbs / 2.2 lbs/kg), the MRD is 381.5 mg (54.5 kg x 7 mg/kg). Each cartridge of 2% lidocaine contains 36 mg of lidocaine (1.8 mL x 20 mg/mL). The patient has already received 2 cartridges of mepivacaine, but since the question asks specifically about additional cartridges of lidocaine, we focus on the lidocaine MRD. To find out how many additional cartridges of lidocaine the patient can receive, divide the MRD by the amount of lidocaine per cartridge: 381.5 mg / 36 mg/cartridge ≈ 10.6 cartridges. Since the patient can't receive a fraction of a cartridge, they can safely receive up to 10 additional cartridges. However, the closest answer choice that reflects the maximum number of full cartridges is 9 (Choice B), as it's the highest number of full cartridges that doesn't exceed the calculated limit.

A 120-Pound Patient Has Received 2 Cartridges of 2% Mepivacaine