Pharm: Local Anesthetics Flashcards
Allergic reactions to what type of local anesthetics is most common due to metabolism to allergy-causing compounds?
How can you tell the type of local anesthetic based on its name?
Ester-type (i.e., benzocaine, cocaine, procaine, and tetracaine)
*Will only have one‘i’ in the name; while amides will have at least two ‘i’s
Which local anesthetics are more prone to hydrolysis and as a result generally have a shorter duration of action?
Ester-type
Use of which substances will reduce systemic absorption of local anesthetics and is useful for those drugs with intermediate or short durations of action (ie., prolongation of action)?
Vasconstrictors (i.e., epinephrine)
Which type of local anesthetic is widely distributed after IV bolus administration?
Amide-type
How does the metabolism of ester-type local anesthetics differ from the amide-type?
- Ester-type are metabolized in plasma
- Amide-type are metabolized in liver and then excreted in urine as charged substances (CYP450)
What is the MOA of local anesthetics?
Where is their receptor site located?
- Block voltage-gated Na+ channel currents and stop spread of AP’s across nerve axons
- Receptor site is at inner vestibule of the sodium channel
What structural properties of some local anesthetics cause a faster rate of interaction with the sodium channel and more potent actions?
Smaller and more lipophilic
*Tetracaine, bupivacaine, and ropivacaine
How does fiber diameter and degree of myelination affect the action of local anesthetics?
List an example
- Preferentially block small fibers
- Myelinated nerves tend to become blocked before unmyelinated nerves of the same diameter
*Preganglionic B fibers are blocked before smaller unmyelinated C fibers
How does firing frequency affect the action of local anesthetics, which are preferntially blocked?
List an example
- Those tha fire at higher frequenciesof depolarization are blockedfirst
- i.e., type A delta and C fibers are blocked earlier than large A alpha fibers
Which is affected first by local anesthetics injected into a bundle of large mixed nerves (sensory or motor)?
Motor nerves
How does the position of sensory fibers within the extremites change from proximal to distal limbs?
- Proximal sensory fibers are located in outer portion of nerve trunk (will be affected first by local anesthetic)
- Distal sensory fibers are located in the core of the nerve (motor fibers will be affected first)
What is block anesthesia and its purpose?
- Injection in major nerve trunks
- Purpose is the anesthetize a region distal to the injection site
What is intravenous regional anesthesia (Bier block) used for?
How is it done?
- Used for short surgeries (<60 min) involving UE and LE’s
- IV injection of agent is placed in a distal vein while circulation of limb is isolated w/ a proximally placed tourniquet
- Large doses of local anesthetic used; tourniquet remains in place to prevent high circulating drug levels causing systemic effects
Which local anesthetic potentiates the effect of NE on α-adrenergic receptors by blocking NET and results in localized vasoconstriction?
Cocaine
*Eliminates need for combining the drug w/ epinephrine
Epinephrine administration to prolong the action of local anesthetics should never be injected into what tissues?
What could this result in?
- Those supplied by end arteries
- Fingers, toes, nose, and penis
- Vasocontriction could cause gangrene
What are the early signs of CNS toxicity caused by local anesthetics?
- Circumoral and tongue numbness
- Metallic taste
High concentrations of local anesthetics in the CNS may have what adverse effects?
- Nystagmus
- Muscular twitching
- Convulsions
- Death by respiratory failure
When large doses of local anesthetics are required premedication with parenteral _____________ can provide prophylaxis against CNS toxicity by raising the seizure threshold
Benzodiazepine (diazepam or midazolam)
Undesired effects of local anesthetics on the CV system are the result of direct effects on ___________ and from indirect effects on the _____________
Undesired effects of local anesthetics on the CV system are the result of direct effects on cardiac and smooth muscle and from indirect effects on the ANS
Local anesthetics block which ion channels in the heart and can have what adverse effects on the heart and blood pressure?
- Block cardiac sodium channels
- Decrease electrical excitability, conduction rate, force of contraction
- Arteriolar dilation —> sytemic hypotension
Cocaine is an exception to the local anesthetic effects on the heart, and instead can cause what?
- Vasconstriction –> local ischemia
- HTN
- Cardiac arrhythmias
Which local anesthetic is the most cardiotoxic due to its long duration of action?
Bupivacaine
Which local anesthetic is a Class Ib antiarrhythmic?
Lidocaine
What are the effects of Lidocaine on the heart?
- Suppresses automaticity of condunction tissue by increasing electrical stimulation threshold of ventricle, His-Purkinje system, and spontaneous depolarization of the ventricles during diastole
- Blocks both the initiation and conduction of nerve impulses by decreasing the neuronal membrane’s permeability to sodium ions, which results in inhibition of depolarization w/ resultant blockade of conduction
What is Benzocaine used for?
- Only as topical agent
- Dermatologic conditions, hemorrhoids, premature ejaculation, and as anesthetic lubricant (i.e., NG an endoscopic tubes/catheters)
Bupivacaine has a tendency to provide more of a (sensory or motor) block?
Sensory
Cocaine, as a local anesthetic, is used primarily how?
Topical anesthtic of the upper respiratory tract
What is Lidocaine used for clinically?
- Alternative choice for pt’s with allergy to ester-type local anesthetics
- Antiarrythmic agent
*Faster, more intense, longer acting, and more extensive anesthesia than an equal dose of Procaine
What is Procaine used for clinically?
Only for infiltration anesthesia (local anesthesia produced by injection of the anesthetic solution directly into the area of terminal nerve endings)
Which local anesthetic is metabolized to a para-aminobenzoic acid, which inhibits the action of sulfonamide antibiotics?
Procaine
Low concentrations of local anesthetics may produce which adverse effects on the CNS?
- Sleepiness (*CIS Q)
- Light-headedness
- Visual and auditory disturbances
- Restlessness
Which local anesthetic is for surface use only?
Benzocaine
*i.e., someone comes in with bad road rash or something
Which 3 local anesthetics have long durations of action?
- Bupivacaine
- Ropivacaine
- Tetracaine
Which local anesthetic has a short duration of action; used only for infiltration anesthesia?
Procaine
