Local Anesthesia
Types of Local Anesthetics
-
Esters (metabolized by plasma cholinesterase)
- Cocaine (out of date)
- Benzocaine
- Procaine
- Tertracaine
-
Amides (metabolized by cytochrome p-450)
- Lidocaine
- Bupivacaine
- Mepivacaine
- Prilocaine
- Ropivacaine
| Drug | Mechanism of Action | Pharmacokinetics | Advantages |
|---|---|---|---|
| Lidocaine | The most commonly used amide type local anesthetic. | Rapid onset and a duration of 60-75 minutes, extended with epinephrine for up to 2 hours. Metabolized in the liver and excreted by the kidneys. | Contraindicated in patients with a known sensitivity. Has also antiarrhythmic action. |
| Bupivacaine | Onset of action is slower than lidocaine and anesthesia is long acting - 2-4 hours, extended with epinephrine for up to 7 hours. | Metabolized in the liver and excreted by the kidneys. | More cardio-toxic than lidocaine, difficult to treat. Contraindication: known hypersensitivity. |
| Ropivacaine | Less toxic, long-lasting LA. | Undergoes extensive hepatic metabolism, with only 1% of the drug eliminated unchanged in the urine. | Ropivacaine is slightly less potent than bupivacaine. |
Local Anesthesia toxicity, and adjuncts
Local Anesthetics
- Mechanism of Action: Reversibly blocking sodium channels to prevent depolarization.
- Lipid Solubility: Potency, plasma protein binding determines, duration of action of local anesthetics.
- Addition of Vasoconstrictor: Prolongation of anesthetic action, decreased risk of toxicity, and decrease in bleeding from surgical manipulation.
Applications of Local Anesthesia
- Nerve block: (e.g., dental and other minor surgical procedures)
- Topical application: To skin for analgesia (e.g., benzocaine) or mucous membranes (for diagnostic procedures)
- Spinal & epidural anesthesia:
- Local infiltration: At end of surgery to produce long-lasting post-surgical analgesia (reduces need for narcotics)
- I/V: For control of cardiac arrhythmias (e.g., lidocaine for ventricular arrhythmias)
Choice of Local Anesthetics
- Onset
- Duration
- Sensory vs. motor block
- Potential for toxicity
All must be preservative free.