Local anesthetics

Local anesthetics bind voltage-gated sodium channels in nerve membranes, so the action potential rises slowly or not at all and impulses stop. Fiber size and myelination set the order of block: pain goes first, then temperature, touch and position sense, and muscle tone last. Lidocaine and bupivacaine are amides, broken down by the liver; epinephrine is often added to slow absorption and lengthen the block.

• LidocaineOne drug, two jobs: a local anesthetic, and, given IV, a class Ib antiarrhythmic for ventricular arrhythmias. The UK formerly called it lignocaine.
• BupivacaineIts long action suits nerve blocks and epidurals, but an accidental intravascular dose can stop the heart, and resuscitation may be difficult or impossible.

• Local and regional anesthesia, including nerve blocks
• Pain relief in labor and after surgery (epidural)
• Numbing skin and mucous membranes (gels, ointments)
• Ventricular arrhythmias (IV lidocaine)

• Seizures at high blood levelsKnown forSerious
• Arrhythmias and cardiac arrestKnown forSerious
• Numb lips and metallic taste, early signs of toxicity
• Ringing in the ears and dizziness
• Low blood pressure
• Slow heart rateSerious
• Breathing depression and arrestSerious
• MethemoglobinemiaSerious
• Drowsiness, then loss of consciousnessSerious
• Allergic reactions (rare with amides)

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Aspirate before injecting and give doses in steps: an accidental injection into a vessel causes systemic toxicity.
• Use lower doses in liver disease, heart block, frailty and old age; amides are cleared by the liver.
• Solutions with epinephrine are used sparingly in fingers, toes, nose, ear and penis, where they can cause ischemia.
• Methemoglobinemia is likelier in G6PD deficiency, infants under 6 months and with oxidizing drugs.

Written for biofideX in plain words, after checking these references:

• Lidocaine HCl injection: label (DailyMed)
• Bupivacaine hydrochloride injection: label (DailyMed)
• Lidocaine hydrochloride and dextrose injection: label (DailyMed)
• Lidocaine (NCI Thesaurus)
• Bupivacaine (NCI Thesaurus)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.