Pharmacology and Anesthesia
This domain covers local anesthetics, vasoconstrictors, drug interactions, and safe dosing. Know the classes and the math of maximum doses.
Core concepts
- Local anesthetics: amides (lidocaine, articaine, mepivacaine, bupivacaine) and esters (benzocaine, procaine). Amides are metabolized in the liver; esters by plasma esterases. Articaine contains a thiophene ring and is metabolized partly by plasma esterases.
- Vasoconstrictors: epinephrine prolongs anesthesia and reduces bleeding; caution in cardiovascular disease and with nonselective beta-blockers.
- Maximum doses: lidocaine with epinephrine ~7 mg/kg (commonly cited 500 mg adult max); articaine ~7 mg/kg; mepivacaine ~6.6 mg/kg. Always calculate by weight and account for epinephrine content.
- Common interactions: epinephrine with beta-blockers, MAO inhibitors, tricyclics; antibiotics with warfarin; NSAIDs with anticoagulants.
- Adverse effects: CNS excitation then depression, cardiovascular effects, methemoglobinemia (benzocaine, prilocaine).
Traps
Questions often test ester vs. amide metabolism, which anesthetic is contraindicated in methemoglobinemia risk, and whether epinephrine is safe in controlled hypertension. Another trap: forgetting to convert cartridge percentages to milligrams.
Rule of thumb
A 1.8 mL cartridge of 2% lidocaine contains 36 mg of anesthetic (2% = 20 mg/mL × 1.8 mL). Multiply concentration (mg/mL) by volume (mL) to get dose.