28 Local anaesthetics Flashcards
28.01 RAPID-ONSET LAs
Lidocaine, mepivacaine, articaine - actions
prevent the propagation of nerve action potentials
block small-diameter pain fibres at lower concentration than large fibres
28.01 RAPID-ONSET LAs
Lidocaine, mepivacaine, articaine - MOA
use-dependent block of voltage-gated Na+ channels from inside of cell membrane
penetrates cell membrane in its lipid-soluble, uncharged form
less active in inflamed tissue, where the lower pH increases ionisation of the weakly basic local anaesthetic (LA)
28.01 RAPID-ONSET LAs
Lidocaine, mepivacaine, articaine - abs/distrib/elim
usually given by injection for rapid effect
penetrates membranes readily
topical application (gel, solution, patch) has slow onset
metabolised mainly in the liver by the P450 system
28.01 RAPID-ONSET LAs
Lidocaine, mepivacaine, articaine - clinical use
surface and infiltration anaesthesia, nerve block (e.g. dentistry) and epidural and spinal anaesthesia (sometimes combined with an opioid)
adrenaline may be added to reduce loss to bloodstream
28.01 RAPID-ONSET LAs
Lidocaine, mepivacaine, articaine - adverse effects
few adverse effects
high plasma concentration may cause seizures and cardiac depression
transient neurologic symptoms are more prevalent with lidocaine than bupivacaine following epidural use
28.02 SLOW- AND MEDIUM-ONSET LAs
Bupivacaine, levobupivacaine, ropivacaine - actions
prevent the propagation of nerve action potentials
block small-diameter pain fibres at lower concentration than large fibres
28.02 SLOW- AND MEDIUM-ONSET LAs
Bupivacaine, levobupivacaine, ropivacaine - MOA
use-dependent block of voltage-gated Na+ channels from inside of cell membrane
penetrates cell membrane in its lipid-soluble, uncharged form
less active in inflamed tissue, where the lower pH increases ionisation of the weakly basic local anaesthetic (LA)
28.02 SLOW- AND MEDIUM-ONSET LAs
Bupivacaine, levobupivacaine, ropivacaine - abs/distrib/elim
these drugs are amides metabolised by the P450 system in the liver, eventually yielding glucuronides
they have a long duration of action of up to 24 hours
28.02 SLOW- AND MEDIUM-ONSET LAs
Bupivacaine, levobupivacaine, ropivacaine - clinical use
infiltration, nerve block, epidural and spinal anaesthesia
used when longer action is required
may be combined with adrenaline to prolong action and with fentanyl for epidural use
28.02 SLOW- AND MEDIUM-ONSET LAs
Bupivacaine, levobupivacaine, ropivacaine - adverse effects
at normal doses, few adverse effects
bupivacaine is more cardiotoxic, whereas levobupivacaine and ropivacaine are considered safer overall and less cardiotoxic
28.03 TOPICAL LA
Benzocaine, tetracaine, lidocaine/prilocaine combination - actions
prevent the propagation of nerve action potentials
block small-diameter pain fibres at lower concentration than large fibres
28.03 TOPICAL LA
Benzocaine, tetracaine, lidocaine/prilocaine combination - MOA
use-dependent block of voltage-gated Na+ channels from inside of cell membrane
penetrates cell membrane in its lipid-soluble, uncharged form
less active in inflamed tissue, where the lower pH increases ionisation of the weakly basic local anaesthetic (LA)
28.03 TOPICAL LA
Benzocaine, tetracaine, lidocaine/prilocaine combination - abs/distrib/elim
ester-type LAs such as benzocaine and tetracaine are, in general, shorter acting, being mainly and rapidly hydrolysed by plasma esterases
topical tetracaine is considered to be faster acting with longer duration than topical lidocaine
28.03 TOPICAL LA
Benzocaine, tetracaine, lidocaine/prilocaine combination - clinical use
tetracaine is used mainly for skin and corneal anaesthesia, whilst benzocaine is used in the mouth/throat
EMLA (eutectic mixture of LA) is a widely used topical combination of lidocaine with prilocaine
28.03 TOPICAL LA
Benzocaine, tetracaine, lidocaine/prilocaine combination - adverse effects
topical LAs are generally safe
ester LAs are more likely than amides to cause an allergic reaction
