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LOCAL ANESTHETICS.docx - كلية الطب البشري‎

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									                                                                   LOCAL ANESTHETICS (LA)

 -used for operative procedures where GA         Struct:                                                        Properties for ideal LA:
 /loss of consciousness is not needed            1)aromatic ring: lipophilic & non-ionizable (easier to         1)has to be water soluble
 /contraindicated                                penetrate through membrane & cells)                            2)has to be sterilized by heat
 *patients with severe respiratory & cvs         2)amine grp: hydrophilic                                       3)should not be irritant
 disease can’t stand GA                          3)amide/ester bond: connecting 1&2                             4)rapid onset of action
 LA: a drug that has the ability to interrupt    Criteria:                                                      5)proper duration of action conveyed during
 pain impulse from the site of                   1)effect should not be accompanied by loss of                  surgical procedure
 operation/site of injury to the CNS             consciousness                                                  6)should not be associated with local/systemic
 -they are weak bases (pka 8-9) except           2)effect should be completely reversible                       toxicity & no local effect
 benzocaine                                      3)should not cause damage to nerve/tissue(where the drug
                                                 is injected)


           DRUG              PHARMACODYNAMIC              PHARMACOKINETIC              THERAPEUTIC             SIDE EFFECTS                    NOTES
                                MODE OF ACTION                                            USES
                                                 +
ESTERS                      *inhibit /reduce Na                                                                                     -main feature of esters:
Procaine                    influx                     -shortest acting                                   -allergic manifestation   hydrolyzed/metabolized by
                                      +
                                 No K leaving cell     (20-30min)                                         (metabolites:             plasma pseudo-
                            Action potential don’t     -poorly absorbed (after                            paraaminobenzoic          cholinesterase enzyme(rapid
                            occur       propagation    SC/ mucus membrane)                                acid)                     hydrolysis, short duration of
                            stopped                    *never used for surface                                                      action)
                            *in hyperkalemia           anesthesia                                                                   -enquire from patient
Tetracaine                  patient: function of LA    -longest acting (1hr/more)                         (All)                     whether he has any
                            is facilitated ( )                                                            -toxicity arises only     sensitivity/allergy while
Cocaine                     [opposite action for                                     -commonly used       when excessive            receiving LA before
Benzocaine                  hypercalcemia]                                           for surface          amount of LA is given     (legnocaine as alternative
                            -LA binds directly to                                    anesthesia           1)Nerve block             for patients with ester
                            their receptors in the                                                        anesthesia: high          allergies)
                                +
                            Na channels                                                                   concentration, small
                            -more effective when                                                          volume
                            channels are open/                                                            2)Infiltration
                            inactive                                                                      anesthesia: low
                            #for a drug to pass &                                                         concentration, high
                            penetrate membrane,                                                           volume
                            E
        DRUG             PHARMACODYNAMIC                 PHARMACOKINETIC            THERAPEUTIC          SIDE EFFECTS                     NOTES
                             MODE OF ACTION                                            USES
AMIDES                   it has to be in lipophilic   *all metabolized by                           -hypersensitivity          (Amides)
(short to long acting)   form                         liver(more time for                            -high concentration       *should be considered in
                         #it will reach site of       metabolism&elimination)                       reach general              patient with liver
Lidocaine/Legnocaine/    action directly/ionized      -intermediate duration of   -can be used as   circulation:-              derangement, HF / receive
Xylocaine                when it passes               action                      anti-arrhythmic   CNS                        β-blocker(more prolonged
                         through, it can reach                                    agent             -inhibitory neuron is      duration of action, delayed
Mepivacaine              site of action only if the                                                 more sensitive, easily     rate of metabolism)
                         channel is open                                                            inhibited
Bupivacaine              -non-ionized can reach       -longest duration of                          -only left with            Factors influencing the
(+vasoconstrictors)DRU   the site of action           action(2hrs)MACOKINETIC                       excitatory neuron          effect of LA:
Prilocaine               directly because it can                                                    -higher concentration,     1)pH value
G                        penetrate the                                                              depression of              -the closer pKa to the pH,
                         membrane.                                                                  excitatory neuron.         the more ionized form we
                         -ionized form can only                                                     *excitation occur first    will have
                         reach the site of action                                                   (tremor, shivering,        *in infection, pH is low
                         when the gates are                                                         convulsion)                Almost all drug will be in
                         open.                                                                      *than depression           ionized form        reduced
                         *use-dependence(they                                                       occur(cardiopulmonary      effect of LA, almost absence
                         are more effective                                                         failure, respiratory       2)lipid solubility
                         when the action                                                            arrest)                    -more lipid soluble, more
                         potential frequency is                                                     CVS                        non-ionizable it will be and
                         right                                                                      -mainly inhibitory         it penetrates tissue easily
                                                                                                    effect                        improve drug potency
                                                                                                    -dilated b/vessels, fall   (less amount of drug is
                                                                                                    in BP, hypotension,        needed)
                                                                                                    tachycardia(patient        3)protein binding
                                                                                                    anxious, agitated)         -if drug is highly protein-
                                                                                                      myocardial,              bound, duration of action is
                                                                                                    respiratory,               prolonged
                                                                                                    cardiopulmonary            -if drug have good
                                                                                                    depression.                diffussibility, onset of action
                                                                                                                               will be shorter
       DRUG          PHARMACODYNAMIC   PHARMACOKINETIC            THERAPEUTIC              SIDE EFFECTS                       NOTES
                      MODE OF ACTION                                 USES
                                                                                     eg: visiting dentist         - we need drug with rapid
                                                                                     -circum-oral/tongue loss     onset of action and longer
                                                                                     of sensation,                duration of action
                                                                                     lightheadedness, tinnitus,   4)the nature, type & length of
                                                                                     visual disturbance           nerve
                                                                                     -finally, unconsciousness+   -small unmyelinated fibers are
                                                                                     complete                     affected first
                                                                                     cardiopulmonary failure      -sequence of sensory loss: pain,
                                                                                                                  temp(cold, warmth), touch ,
                                                                                                                  deep pressure, motor
                                                                                                                  -recovery in reverse order
Types of LA                            -use drug topically on   *Legnocaine: all                                  Eutectic Mixture of LA
1.Topical                              mucus                    forms of LA                                       (EMLA)=Legnocaine+Prilocaine
Anesthesia/surface                     membrane(nose,           *Benzocaine &                                      -combined in certain
anesthesia                             mouth, bronchial         Cocaine: only used                                concentration (5% or 2.5%)
                                       tree, urethra)           for surface                                        -useful to anesthesize skin but
                                       -use as spray            anesthesia                                        not mucus membrane
                                       /paste/cream/gel         *Procaine: not                                     -action is completed within 1hr
                                       -very rapid              used as surface                                   and last for 1hr
                                       absorption, may be       anesthesia (not                                   -Local infiltration: inject the
                                       associated with toxic    absorbed)                                         drug in SC (low conc, high
                                       manifestation (occur                                                       volume)       sensory loss
                                       in patient using                                                           [used when suturing
                                       urethral                                                                   wound/cut]
                                       catherization,                                                             -Nerve block: injecting drug
                                       especially when done                                                       around nerve trunk, at higher
                                       with metal dilators,                                                       up      sensory + motor loss
                                       more when patient                                                          [dentist anesthesize nerve at
                                       have obstruction at                                                        angle of jaw]
                                       urethra/bladder
                                       more force ,needed
                                       need to use more LA)
        DRUG           PHARMACODYNAMIC   PHARMACOKINETIC         THERAPEUTIC USES              SIDE EFFECTS                        NOTES
                        MODE OF ACTION
2.Epidural/Peridural                     -LA injected close to   -production of                                        -less possibility for infection/
                                         nerve roots around      painless childbirth                                   contamination of spinal fluid
                                         the spinal cord                                                               compared to spinal anesthesia
3.Spinal anesthesia                      -inject drug into the                          -leak of CSF from site of
                                         spinal fluid                                   injection(unlikely to occur)
                                                                                        -respiratory
                                                                                        depression(when reaching
                                                                                        phrenic nerve)
                                                                                        *be careful, the more tilt
                                                                                        patient’s head, the higher
                                                                                        level will be anesthesized
                                                                                        Common:
                                                                                        1.bradycardia,
                                                                                        hypotension (affect of α-
                                                                                        blocker agonist)
                                                                                        2.urinary retention
VASOCONSTRICTORS                                                 -prevent /delay        -ischemia & gangrene (in
-Epinephrine                                                     rapid absorption of    terminal part: ear, penis,
-Adrenaline                                                      drug from systemic     finger…)
                                                                 circulation&              Never use a
                                                                 possibility of toxic   vasoconstrictor in nerve
                                                                 manifestation          block in terminal organ
                                                                 -to keep the drug in
                                                                 contact with the
                                                                 nerve      prolong
                                                                 duration of action

								
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