Local Anesthetic Drugs Flashcards
What is the elimination half life of prilocaine, lidocaine and bupivacaine?
Prilocaine: fastest (elimination ½ t 96 min) versus lidocaine (96 min) versus bupivacaine (210 min)
What is the onset of lidocaine?
Rapid onset
What is the duration after inflitration of lidocaine?
60-120 min
What is the pKa and protein binding of Lidocaine?
Protein binding 70%; pKa 7.9
What is the max dose of lidocaine?
300 mg (5mg/kg plain; 7 mg/kg with epi)
What is the clinical concentrations of lidocaine?
- Topical spray 4%
- Topical gel 2%
- Infiltration 0.5-1%
- Tracheal (LTA) 4%
- Spinal 5%
- Epidural 1-2%
- IV Bier block 0.5%
What is the metabolism of lidocaine?
liver mainly CYP 34A (dealkylation) to main active metabolite monoethylglycinexylidide (MEGX) and lesser metabolite xylidide (10% active)
What accounts for the prolonged antidysrhythmic properties of lidocaine?
active metabolite monoethyl
What impact does hepatic disease have on lidocaine?
Affected by hepatic disease/⬇️ hepatic blood flow (5 fold)
Why has use of lidocaine with spinals decreased?
Use for spinal anesthesia has declined due to concerns about neurotoxicity and transient neurological symptoms (TNS)
What is the most concern with lidocaine?
Causes vasodilation at most concentrations
What can be added to lidocaine to prevent the vasodilation?
The addition of epinephrine can significantly reduce absorption of lidocaine by nearby vessels, allowing more of the initially administered dose to enter the neural compartment, thereby prolonging the duration of action by as much as 50%
What is true about clearance of lidocaine and pregnancy?
Maternal clearance of lidocaine is prolonged in the presence of pregnancy-induced hypertension
What is prilocaine similar to?
Similar clinical profile as lidocaine
What are the uses of prilocaine?
Used for infiltration, peripheral nerve blocks (PNB), spinal, and epidural anesthesia
What is different with prilocaine then with lidocaine?
Causes significantly less vasodilation than lidocaine
What is not needed with prilocaine?
Addition of epinephrine is not necessary to prolong duration of action
What characteristic is specific to prilocaine?
Least systemic toxicity of all amide local anesthetics
What can prilocaine cause?
Can cause methemoglobinemia (>600 mg dose) due to its metabolite orthotoluidine (Limits its clinical usefulness)
What is orthotoludiine?
converts hemoglobin to its oxidized form, methemoglobin
How will a patient present with methemoglobinemia?
Patient may appear cyanotic and oxygen carrying capacity is decreased
What is the treatment for Methemeglobinemia?
readily reversed by administering methylene blue 1-2 mg/kg IV over 5 minutes (do not exceed 7-8 mg/kg)
What shift will occur on the oxyhemoglobin curve with Methemeglobinemia?
Left shift of oxygen-dissociation curve
What other substances are associated with Methemeglobinemia?
- Topical local anesthetics (benzocaine, prilocaine, lidocaine)
- NTG
- Phenytoin
- Sulfonamides
Central cyanosis occurs when methemoglobin concentrations exceed ________%
15%
When is Methemeglobinemia
suspected?
Suspect when oxygen “saturation gap” between arterial blood saturation and pulse oximetry; dx w/ co-oximetry
How does Methylene blue treat Methemoglobinemia?
acts as electron donor and nonenzymatically reduces methemoglobin to hemoglobin
When should normal Normal levels of methemoglobin be reached after methylene blue administration?
20-60 minutes
What is true regarding the effects of methemoglobinemia as methylene blue is cleared?
Effects is short-lived as methylene blue cleared before total conversion
What is the pharmacological properties of mepivacaine (Carbocaine)?
Pharmacologic properties similar to lidocaine-Longer duration of action
Why should mepivacaine (Carbocaine) not be used for obstetric anesthesia?
- Metabolism is prolonged (leading to a decrease in clearance) in the fetus and newborn
- pKa 7.6 – crosses placenta
What is not needed with mepivacaine (Carbocaine)?
Lacks vasodilator activity – no need to add epinephrine (alternative when epi is not recommended)
What is the onset of Bupivacaine (Marcaine)?
Slow Onset
What is the duration after infiltration of Bupivacaine (Marcaine)?
240-480 min
What is the protein binding and pKa of Bupivacaine (Marcaine)?
Protein binding: 95%; pKa 8.1
What is the max dose of Bupivacaine (Marcaine)?
175 mg (2.5 mg/kg plain; 3mg/kg with epi)
What is the chemical structure of Bupivacaine (Marcaine)?
Racemic mixture of both the R and S enantiomers, provides prolonged and intense sensory analgesia which often outlasts the motor block
What is Bupivacaine (Marcaine) used for?
Used in infiltration, PNBs, spinals, epidurals
What is the concentration of epidural analgesia and anesthesia with Bupivacaine (Marcaine)?
Epidural analgesia and anesthesia: used in concentrations of 0.25-0.5% with a 2-5 hour duration of action
What the duration of PNBs with Bupivacaine (Marcaine)?
12-24 hours
What is the characteristics of the intrathecal use of Bupivacaine (Marcaine)?
- provides 2-3 hours of anesthesia and 4-6 hours of analgesia
- Epinephrine sometimes added as a marker for intravascular injection and to prolong duration of action
What are the metabolisms of Bupivacaine (Marcaine)?
Possible pathways for metabolism include aromatic hydroxylation, N-dealkylation, amide hydrolysis, and conjugation
What is the most important plasma protein binding site of Bupivacaine (Marcaine)?
Alpha 1 –acid glycoprotein,
96% protein bound
What has been reported with Bupivacaine (Marcaine)?
- Reports of sudden cardiac arrest associated with significant morbidity and mortality
- Due to high affinity for Na+ channels and high lipid solubility
When is the 0.75% concentration of Bupivacaine (Marcaine) not used?
in labor epidurals because of the associated mortality/toxicity
What is liposomal local anesthetics?
incorporating local anesthetic into liposomes for the purpose of prolonging the duration of action and decrease toxicity
What is the goal of liposomal local anesthetics (bupivacaine)?
to upload higher amount of local anesthetic into the liposome molecule and have a consistent release of local anesthetic in the tissues;
What are the pk of liposomes?
liposomes are hydrophobic-based polymer particles which are then combined with a LA