Esters
1. Cocaine
ï€ It is used only in topical anesthesia.
ï€ It is used directly in superficial anesthesia of ear-nose-throat, ulcer and wound.
ï€ It is a local anesthetic that produces vasoconstriction. It produces vasoconstriction due to local inhibition of noradrenaline reuptake.
ï€ Other local anesthetics that cause vasoconstriction without adrenaline are bupivacaine and ropivacaine.
ï€ May cause hyperpyrexia.
ï€ May cause methemoglobinemia.
ï€ It produces bradycardia with vagus central stimulation at low doses and tachycardia at high doses.
2. Procaine
ï€ It is a local anesthetic with the weakest potency.
ï€ It is the shortest lasting local anesthetic agent.
ï€ It is the local anesthetic substance that most often causes allergic reactions.
ï€ It should not be administered to people taking sulfonamide therapy as it is converted to PABA in the body.
3. Chloroprocaine
ï€ It is contraindicated to use in spinal anaesthesia.
ï€ It is not used topically.
ï€ Epidural and intrathecal administration is not recommended as it may cause permanent neuronal damage.
ï€ Its effect starts quickly and lasts for a short time.
4. Benzocaine
ï€ It is used only superficially.
ï€ It can be applied directly to wounds and ulcers.
ï€ May cause methemoglobinemia.
5. Tetkacaine, Oxybuprocaine, Hexylcaine, Piperocaine etc
Those Made of Amide
• They should not be used in patients with liver disorders and with drugs that reduce liver blood flow, such as propranolol.
• This group of drugs bind to al-acid glycoprotein in plasma. Since this protein is low in infants; They are more sensitive to LAs.
1. Lidocaine
ï€ It can be applied in all types of local anesthesia.
ï€ Its effect starts quickly.
ï€ It can be used intravenously (without adrenaline) as an antiarrhythmic.
ï€ It is broken down in the liver, the formed monoethylglycine xylidide and glycine xylidide metabolites have a toxic effect on the CNS (the earliest sign is nystagmus).
ï€ Its use in subarachnoid block is limited due to transient neurologic symptoms.
ï€ It is excreted through the kidneys.
ï€ It should not be used in people susceptible to malignant hyperthermia, as it accelerates the release of calcium from the sarcoplasmic reticulum.
2. Prilocaine
ï€ Prilocaine is used in infiltration, peripheral nerve blocks, spinal and epidural anesthesia.
ï€ Due to its high clearance, it causes the least systemic toxicity of all amide local anesthetics and is therefore more preferred for intravenous regional anaesthesia.
ï€ Together with lidocaine is the most appropriate drug for regional intravenous anesthesia.
ï€ Toluidine metabolite formed in the body creates methemoglobinemia.
ï€ If methemoglobinemia develops, it is treated with iv methylene blue.
ï€ It cannot be used in obstetrics, COPD and cyanotic heart diseases.
3. Mepivacaine
ï€ It has a clinical profile similar to lidocaine, but has a slightly longer duration of action because it causes less vasodilation.
ï€ It is not used in obstetrics as it is toxic to the baby.
4. Bupivacaine
ï€ Bupivacaine is the most lipid soluble local anesthetic, which is the structural homologue of mepivacaine.
ï€ Its selectivity to sensory nerve fibers is very high. It provides prolonged sensory anesthesia and analgesia.
ï€ Typically the depth and duration of motor block is longer, especially when used with continuous infusion at low concentrations.
ï€ It is the strongest (longest acting) of those used systemically.
ï€ It is the most cardiotoxic local anesthetic.
ï€ It is widely used in subarachnoid anesthesia and typically has a duration of action of 2-3 hours.
ï€ In contrast to lidocaine and mepivacaine, transient neurological symptoms are very rare.
ï€ It is used for infiltration anesthesia, nerve block, spinal, epidural and caudal anesthesia.
5. Etidocaine
ï€ It is the most lipophilic of the local anesthetics.
ï€ It provides a good motor block, makes very obvious muscle relaxation.
6. Ropivacaine:
ï€ Ropivacaine is the structural homologue of bupivacaine and mepivacaine.
ï€ Its fat solubility is lower than bupivacaine.
ï€ It is clinically equal in strength with bupivacaine in sensory blockade, but motor block starts more slowly and is of shorter duration.
ï€ It has a less cardiotoxic profile compared to bupivacaine.
ï€ Having a natural vasoconstrictive effect causes a decrease in cardiotoxic profile and prolongation of its duration of action.
ï€ It is more selective to sensory nerve fibers than motor nerve fibers (like Bupivacaine).
ï€ It is long-acting LA.
ï€ It is used in spinal and regional anesthesia.
7. Levobupivacaine
ï€ It is the C-enantiomer of racemic bupivacaine.
ï€ Clinically similar to bupivacai.
ï€ Less cardiotoxic than bupivacaine.
8. Dibucaine
ï€ It is the strongest of local anesthetics in terms of gravimetric potency.
ï€ It is one of the most potent and most toxic local anesthetics.
Properties of local anesthetics | |||||
local anesthetic | structure | Usage area | Effect duration | Effect onset | Feature |
Cocaine | Ester | topical | *** | *** | vasoconstriction |
benzocaine | Ester | topical | *** | *** | Topical use only, methemoglobinemia |
procaine | Ester | Topical, infiltration, spinal | Short | Slow | Causes allergies, the shortest and weakest effect |
chlorprocaine | Ester | Infiltration, peripheral nerve block, epidural, spinal (?) | Short | Fast | Spinal use is controversial |
Tetracaine (amethocaine) | Ester | Topical, Spinal | Long | Slow | Very long spinal anesthesia |
dipucaine | amide | Topical, Spinal | Long | Slow | Quite potent and highly toxic |
Etidocaine | amide | Infiltration, peripheral nerve block, epidural | Long | Fast | Most lipophilic LA |
lidocaine | amide | Topical, infiltration, peripheral nerve block, spinal, epidural | Middle | Fast | SSS toxic, antiarrhythmic iv can be used in IVRA |
mepivacaine | amide | infiltration, peripheral nerve block, spinal, epidural | Middle | Slow | Toxic to newborn |
Prilocaine | amide | Infiltration, peripheral nerve block, epidural | Middle | Fast | Methemoglobinemia can be used in IVRA |
bupivacaine | amide | Infiltration, peripheral nerve block, spinal, epidural | Long | Middle | most cardiotoxic |
Ropivacaine | amide | Infiltration, peripheral nerve block, spinal, epidural | Long | Middle | Sensory selective, vasoconstriction |
Levobupivacaine | amide | Major peripheral nerve block, spinal, epidural | Long | Middle | Less cardiotoxic effect |
Side Effects and Toxicity of Local Anesthetics
Systemic Side Effects
• Initially, numbness, dizziness, restlessness, irritability and muscle twitches are seen in the tongue and around the mouth.
• This is followed by convulsions, loss of consciousness.
• Finally, apnea, cardiovascular collapse and coma develop due to medullary depression.
• They can cause intracardiac block and cardiac arrest (especially bupivacaine).
• They may cause hypotension due to sympathetic blockade (especially during spinal and epidural anaesthesia).
• They can cause allergic reactions, mostly seen in ester structures.
• They initially produce a depressant effect in CVS and CNS (except for cocaine, this substance causes euphoria).
• They cause disinhibition-related excitation (tonic-clonic convulsions) at high doses.
• Hypotension (which happens most prominently during spinal anaesthesia)
• Cardiac arrhythmias and cardiac arrest (Bupivacaine)
• Toxic effects on CNS (Lidocaine)
• Increase in body temperature
• Allergic reactions to esters are common (Procaine, Tetracaine).
• P-aminobenzoic acid, which is formed by the breakdown of esters, is responsible for the allergy. (PABA).
Local Anesthetic Systemic Toxicity (LAST) treatment:
• The initial basic treatment required for CNS toxicity is supportive therapy.
• Adequate oxygenation and ventilation should be maintained, and the airway should be secured if necessary.
• Convulsions that persist despite adequate ventilation and oxygenation should be treated with sedative hypnotic agents such as midazolam and propofol. If there is no improvement despite this, a neuromuscular blocker is used to end severe muscle activity.
• In case of cardiac arrest due to LAST, standard advanced cardiac life support should be applied.
• Vasopressin is not recommended and adrenaline is preferred initially.
• If ventricular dysrhythmias develop, amiodarone should be preferred instead of lidocaine.
• Severe CVS toxicity from bupivacaine is resistant to standard resuscitation. In this case, cardiopulmonary bypass should be considered at an early stage for the effective treatment of life-threatening dysrhythmia and cardiovascular collapse.
• It has been shown that intravenous intralipid emulsion significantly reduces bupivacaine-induced CVS toxicity.
