Local anesthetics and analgesics
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Anesthetics with high potency?
Bupivicaine and Tetracaine
High pKa, moderate rate of onset but LONG duration
Two theories of mode of action of anesthetics?
1. Membrane expansion theory: lipophilic anesthetics inciorporate themselves into membrane
- 2. (Major) receptor mechanism: physical occulsion of na channel
- a. allosterically mediated
- b. distort local electrical field
The blockade of Na conductance is the basis of local anesthetic action
What is an additional contributing mechanism to blockade of Na conductance?
Physiochemical interaction of the base form with membrane
What is the differential nerve blockade by anesthetics?
Autonomic loss first (that is why we give epi to constrict because autonomics shutdown)
What are the factors contributing to the differential nerve blockade?
- 1. fiber length
- 2. use-dependent block
- 3. peripheral nerve organization
- 4. local anesthetic selectivity
How to delay anesthetics rate of absorption?
Sympathomimetic agents are topically ineffective
Distribution of local anesthetics?
- 1.bind to plasma proteins
- 2. Unbound diffuses to tissues freely
- 3. Enter CNS and can cross placenta
- a. lido, prilo, etido Cat B
- b. Mepiv, Bupi Cat C
Metabolism of local anesthetics?
Esters by plasma cholinesterase
Amides by hepatic oxidase system (lido T1/2 1.5-3.5hrs but Tetra is 25 minutes because it has an ester)
Metabolite of prilocaine, articaine, benzocaine (O-toluidine) can cause methehemeglobinemia
Lido has some metabolites too that are toxic
Excretion of local anesthetics?
Inversely to their protein binding
Inversely to the pH of urin
Cardivascular toxicity of local anesthetics?
Lipophilic ones like etido and bupivacaine
depress myocardial contractility
note: locally do affect myogenic activity and autonomic tone
Dosage calculation, Clark's rule?
Based on child's body weight
Or Young's rule which is based on patient's age
Maximum does for lido with epi?
7mg/kg max of 500mg
lido no epi 3mg/kg 300mg max
What is inside a carpule of anesthetic?
- 1. Local anest
- 2. Vasoconstrictor
- 3. Metabisulfite (only if epi present)
- 4. Isotonic NaCl
- 5. HCL or NaOH to adjust pH
Drug interactions and local anesthetics?
CNS acting agents can cause permanent deficits
Drug interactions with epi in anesthetic?
potential elevation of BP with tricyclic antidep
NO interaction with epi and MOA
also...alpha blocker (epi reversal=hypotension)
beta blocker (vasoconstriction with epi causing hypertension)
What is Oraverse?
alpha-adrenergic blocking agent, vasodilates removes anesthetic quicker from site
BUT will not reverse CNS and cardio effects
Adverse effects of articaine and prilocaine?
Effects of aspirin?
Antipyretic, analgesic, antiinflammatory, antiplatelet
Can cause analgesic nephropathy, reye's syndrome, GI bleeding
Diflunisal: derivative of salicylic acid
not metabolized to salicylate
What does chronic toxicity of aspirin look like?
Tinnitis, nausea, headache, hyperventiliation, confusion
IRREVERSIBLE binding to COX
Acute toxicity of aspirin?
Hyperthermia, respiratory alkalosis, acidosis
TX: alkalization of urine, gastric lavage, respiratory support
Aspirin intolerance signs?
Rhinitis to severe asthma because lipoxygenase pathway is predominating
DO NOT switch to NSAIDs since they are cross-sensitive
antipyretic, analgesic, but little antiinflammatory effects (that is it is good for aspirin sensitive folks, no COX blocking)
Adverse effects of tylenol?
Hepatotoxicity (metabolite n-acetyl-benzoquinoneimine), max 4g/day
Tx: gastric lavage, within 36hrs give n-acetylcysteine
adverse effects like aspirin but REVERSIBLY binds to COX
ALL NSAIDS have ceiling effect! you give more and less therapy but more side effects
Contraindications of NSAIDs?
Hematologic malignancies w/thrombocytopenia
NSAID mainly formulated for IV use
no more than 5 days due to risk of renal toxicity, has anitplatelet activity
Plant of opium and percent drugs?
What are opiates?
alkaloids derived and isolated from opium
What are opioids?
Morphine like pharm properties but not derived from opium
This and opiates are now called opioid analgesics
Name naturally occuring opiates?
Opium, morphine, codeine
Name semisynthetic opioids?
Heroin, hydromorphone, hydrocodone, oxycodone
Synthetic opioids (fully)?
Meperidine, Fentanyl, sufentanyl (extremely potent, the last two)
Name narcotic antagonists?
Endofenous opioid peptides, rank in order of size?
Four types, many subtypes
- Main is mu
- mu1 is supraspinal
- mu2 is spinal analgeisa
Where do opioids provide analgesia?
Central and peripheral (not neuropathic or sharp)
no ceiling effects
effective against continuous, dull, aching pain
What does aging do to pharm effects of opioids?>
- 1. dec sensitivity to pain
- 2. reduced ability to clear morphine
- 3. more pain relief with dose compared to younger patient
Respiratory effects of opioids?
Dec in tidal volume and rate
dec response of brainstem to CO2 tension
cough suppression and opioids?
Side effect, but wanted
codeine and dextrometrophan
supression is lower does than needed for analgesic eeffect or respiratory effect
Pupillary constriction and opioids?
No tolerance to this excitation
pinpoint pupils in addicts
Nausea and opioids?
Vomiting, stimulate CTZ in medulla causing emesis
vestibular component, if patient lays down all good but not when walking
Opioids and GI tract?
Constipation, inc sm tone and dec propulsive motility
Billary spasms, inhibits intestinal hypersecretion (great for diarrhea tx)
Opioids and other smooth muscles?
Dec urine flow due to effects on sm cells of ureter, bladder, uterus
Opioids and asthma?
May propentiate, due to histamine release
Opioids and CV system?
Dec BP due to hypoxia (vasodilation to counteract)
Dec peripheral vascular tone (helps in pulmonary edema)
Therapeutic use for morphine?
Therapeutic use for codeine?
Inc oral effectiveness (60% bioavailable)due to methoxy group
analgesic postoperative (30-60mg), antitussive (15-20mg)
10 morphine=120mg codeine
biotransformation is inhibited by cimetidine or antidepressants
Mepiridine side effects?
Poor CV stability during IV
Acute intoxication is CNS excitation (tremors, convulsions opposite of coma and stupor with morphine)
must be given IV, poor orally
Mepiridine and pupils and billary?
Less pupillary and billary due to atropine like activity
Therapeutics of fentanyl?
80-100 times more potent due to lipid soluble, short duration of action
ADVantage: cardiac stability, reduces endocrine response to surgery
Short acting IV admin
antidote for respiratory depression
Long acting- oral admin
48-72 hrs effectiveness
Therapuetics of pentazocine?
agonist at K and partial agonist or weak antagonist at mu recpetors
new drug Talwin has this and naloxone to prevent injection abuse.
Side effects of pentazocine?
Less potent than morphine
Can increase HR and BP, unlike other opioids
does not cause as severe resp depression
Therapuetics of Tramadol?
weak Mu agonist and reuptake of NE and 5HT
mod-severe pain, good orally
n/v and drowsiness common side effects
Therapeutics of Tapentadol?
Opioid agonist and inhibits NE reuptake
schedule II drug
not first line drug
Nitrous oxide therapuetics?
Analgesic: mobilizes endogenous opioids
Anxiolytic: GABA inhibition
Benefits of NO2?
Rapid induction and recovery
High MAC 100% low potency, can be titrated
protects cough reflex
Adverse effects of NO2?
n/v worsened by longer duration, inc concentration, or fluctations of administration
fasting not necesssary but light meal recommeneded
What is a sedative?
drowsiness, relaxation, calmness, dev motor activity with no loss of consciousness
What is hypnosis?
loss of unconsciousness that resembles natural sleep, dec motoractivity, impaired sensory responsiveness
Which benzos used for surgical adjuncts in conscious sedation?
Diazepam and Midazolam
Which benzos to treat skeletal m uscle spasm?
Diazepam and chlordiazepoxide
Which benzos used to treat tension, insomnia, and anxiety?
alprazolam, diazepam, triazolam, oxazepam
Skeletal muscle spasms and site of action by benzos?
site of action is subcortical but evidence of spinal interneurons are also affected
All benzos cause anterograde amnesia
Side effect of midazolam?
respiratory depression and apnea, worse with opioid
Adverse effects of benzos?
CNS depression (elderly more susceptible)
inc incidence of nightmares, hyperactivity, insomnia
What antihistamines are given to children?
Hydroxyzine and Promethazine,
hydroxy: also anticholinergic
Psychosocial or behavioral factors may contribute to the perception of chronic craniofacial or dental pain.
(e.g. SOMATOFORM PAIN DISORDER and MUNCHAUSEN SYNDROME.
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