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113 Cards in this Set

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barbiturates
phenobarbital
pentobarbital
methohexital
thiopental
thiamylal
alpha-2 agonists
xylazine
medetomidine
detomidine
benzodiazepines
diazepam
clonazepam
zolazepam
midazolam
dissociative anesthetics
ketamine
tiletamine
neuroleptics
phenothiazines: acepromazine, chlorpromazine

butyrophenones: droperidol
pure opioid agonists
morphine
hydromorphone (oxymorphone)
etorphine
codeine
dextromethorphan
methadone
carfentanil
sufentanil
fentanyl
pure opioid antagonists
naloxone
naltrexone
diprenorphine
mixed opioid agonists/antagonists
butorphanol
buprenorphine
miscellaneous opioids
loperamide
apomorphine
inhalational anesthesetics
halothane
isoflurane
sevoflurane
nitrous oxide
analeptics
doxapram
strychnine
theophylline
aminophylline
theobromine
local anesthetics
esters: cocaine, proparacaine
amides: lidocaine, bupivacaine, mepivacaine
anticonvulsants
phenobarbital
primidone
diazepam
clonazepam
potassium bromide
felbamate
gabapentin
phenobarbital
barbiturate

used to tx seizure disorders in dogs & cats; occasionally used as oral sedative
pentobarbital
barbiturate

sedative agent, drug of choice for tx of intractable seizures in dogs & cats d/t convulsant agents (ex. strychnine poisoning) or CNS toxins (ex. tetanus), major active ingredient in several euthanasia solutions

largely replaced by ultra-short acting barbiturates b/c of slow induction, long duration of action, inactivated primarily by metabolism (don't use w/ liver dz)
thiopental
barbiturate

ultra short acting
excellent IV induction agent in young, healthy animals, or alone for very short procedures
thiamylal
barbiturate

ultra short acting
no longer available in US; replaced by thiopental
methohexital
barbiturate

ultra-short acting anesthetic agent often used in sight hounds b/c it does not depend on redistribution to fat to reverse effect
etomidate
ultrashort acting, hypnotic non-barbiturate induction agent

excellent induction agent for patients w/ CV, respiratory, or liver dz

safe for use in sighthounds

depresses cortisol production
can't use in horses (excitement)
propofol: facts + pros
non-barbiturate sedative-hypnotic agent

used for induction &/or maintenance of anesthesia, to produce prolonged sedation of patients in ICU

pros: rapidly metabolized & redistributed --> very rapid recovery
does NOT accumulate in body w/ chronic dosing
barbiturates & lipid solubility
thiobarbiturate always more lipid soluble than oxybarbiturate

phenobarb<pentobarb<thiopental

as lipid solubility increases:
1. duration of action decreases
2. quicker onset
3. increased rate of distribution, metabolism
4. more hypnotic potency
5. more protein binding
barbiturates: metabolism & redistribution
renal excretion: if highly lipid soluble, completely reabsorbed --> metabolized in liver (caution w/ liver dz)

redistribution occurs if drug given rapidly (ex. IV), highly lipid soluble: drug goes to high flow organs 1st, then rapid reversal to muscle, adipose
clinical uses of barbiturates
induction
tx of seizures
to decrease ICP & tx cerebral edema
euthanasia
cons of barbiturates
NOT analgesic (HYPERalgesic at subanesthetic doses)
contraindicated w/ liver dz d/t metabolism, inc. free drug if hypoproteinemia is present
can't use thiobarbiturates in sighthounds
induce liver microsomal enzymes --> incr. metabolism of other drugs (phenobarb most potent)
given only IV or PO
w/ multiple dosing --> longer duration
no pharmalogical antagonist (phenobarb OD: give bicarb to alkaline urine --> increased rate of excretion of parent drug)
CV, resp. effects of barbiturates
brief hypotension, reflex tachycardia
transient resp. depression (+/- apnea)
arrhythmias, esp. in excited animals
clinical uses of alpha-2 agonists
preanesthetic agent
chemical restraint

selectivity: xylazine < detomidine < medetomidine

duration: detomidine longest
effects of alpha-2 agonists
increases potency of other anasthetic drugs
sedation/hypnosis
analgesia
muscle relaxation
adverse effects of alpha-2 agonists
emesis
resp. depression
CV effects (vary b'twn drugs)
bloat
hyperglycemia
increased urine output
don't use xylazine during last mo. of pregnancy
CV effects of xylazine
transient hypertension followed by prolonged hypotension
bradycardia
arrhythmias
clinical uses of guaifenesin
adjunct to anesthesia in horses (IV)
effects of guaifenesin
sedation/hypnosis
analgesia
muscle relaxation
antipyretic
antitussive
pros & cons of guifenesin
pros: inc. potency of barbiturates
dec. hypertonicity assoc. w/ ketamine
little cardiopulmonary depression

cons: not very H2O soluble --> large vols. required
may hemolyze RBCs (esp. in cattle)
clinical uses of benzodiazepines
pre-anesthetic med (often w/ opioids)
tx of seizures (midazolam: neonatal seizures in foals)
tx anorexia in cats
tx fears & phobias
pros of benzodiazepines
dec. dose of other anesthetic drugs
muscle relaxant
weak resp. depression
minor CV effects
cons of benzodiazepines
cannot give IM (except midazolam)
weaker sedative/hypnotic effects than other meds
amnesia
can't give oral diazepam to cats --> idiopathic hepatic necrosis
avoid ending chronic tx abruptly
tolerance w/ chronic use
IV midazolam in cats --> profound tachycardia
pharmacokinetics of benzodiazepines
lipid soluble --> extensive redistribution when given IV

metabolism:
oxidative pathway --> many active metabolites
reductive path --> inactive compounds

midazolam: short duration d/t rapid metab & distribution
mechanism of action of benzodiazpines
facilitates GABA by binding to site on GABA receptor --> inc. affinity of GABA for receptor & vice versa --> GABA produces inc. in chloride conductance
flumazenil
benzodiazepine receptor antagonist

useful in sick animals, esp. cats, to speed up recovery from anesthesia
mechanism of action of barbiturates
low doses: facilitates GABA by binding to site on GABA receptor (separate site from benzos)

higher doses (anesthetic):
decreases presynaptic release of NTs
blocks postsynaptic action of excitatory NTs
GABA-mimetic effect
dissociative anesthetic state
eyes open
involuntary movements
vocalization
hallucinations
feel separated from body
physiological effects of dissociatives
analgesia (mostly somatic, less visceral)
sympathetic activation
hypertonicity (use w/ benzos, alpha-2s, or guaifenesin)
inc. ICP, IOP
convulsions (use w/ benzos)
apneustic breathing
retention of near normal pharyngeal & laryngeal reflexes
mechanism of acation of dissociatives
noncompetitive antagonists of NMDA glutamate receptor --> inc. activity of layer V pyramidal output neurons (that release glutamate) --> disruption of thalamic & cerebral functions
tiletamine
similar to ketamine, but longer duration of action

can only be bought mixed w/ benzo zolazepam = Telazol (recoveries may be prolonged & rough)
clinical uses of neuroleptics
chemical restraint
preanesthetic meds (dec. dose of other meds)
antiemetic
neuroleptic syndrome
sedation
tranquilization
dec. emotional behavior
dec. responsiveness to external stimuli
dec. spontaneous movement
NOT hypnotic
NO analgesia alone
adverse effects of neurolpetics
extrapyramidal effects: dyskinesia, dystonia, muscle tremors
higher doses --> catalepsy
hypotension
hypothermia
mild neg. inotropic effect
dec. seizure threshold
weak resp. depression, but can inc. resp. depression w/ other drugs
mechanism of action of neuroleptics
antagonize dopaminergic, alpha-adrenergic, muscarinic, H1, certain serotonergic receptors
phenothiazine neuroleptics: effects in horses
ace, chlorpromazine

can cause violent incoordination & excitement

penile prolapse & priapism
droperidol
butyrophenone neuroleptic

used in various preps in SA, swine
don't use in horses d/t bizarre rxns
shorter duration than phenothiazine neuroleptics
potent dopamine receptor antagonists --> more likely to produce extrapyramidal effects
mechanism of action of opioids & opiopeptins
decrease release of substance P --> dec. transmission of nociceptive info
species dependent effects of morphine
dogs, monkey, man: analgesia, sedation, euphoria, pupillary miosis

horses, cats, pigs, ruminants: analgesia, excitement, dysphoria, mydriasis (use low doses)
pros of morphine
valuable premed b/c dec. amt. of other drugs
antitussive
mild hypotension, bradycardia
cons of morphine
dose dependent resp. depression: CAUTION w/ lung dz, neonates
constipation, esp. w/ chronic use
emetic
SEVERE hypotension if in shock or w/ volume depletion
hydromorphone
pure opioid agonist

similar to morphine, but 5x more potent

less GI upset & vomiting than morphine in dogs
etorphine
pure opioid agonist

agonist at all receptors, 1000x more potent than morphine

used only to immobilize wild animals
codeine
pure opioid agonist

10x weaker than morphine
protected from 1st pass metabolism in liver --> converted to morphine

uses:
antitussive
w/ acetaminophen to relieve pain in dogs
dextromethorphan
pure opioid agonist

devoid of all opioid properties except ANTITUSSIVE effect
meperidine
pure opioid agonist (=Demerol)

effective analgesic, maintains much of potency when given PO
less constipating than morphine
methadone
pure opioid agonist

accumulates in body --> inc. duration of action w/ multiple doses
retains most analgesic potency when given orally
tolerance, dependence develop slowly
also NMBA glutamate antagonist --> dec. opioid dependence
carfentanil
pure opioid agonist

most potent of fentanil family (all are short acting, w/ rapid onset)

used to immobilize wild animals
sufentanil
pure opioid agonist

anesthetic adjunct in dogs
fentanyl
pure opioid agonist

anesthetic adjunct in dogs
patches: control of chronic pain (absorption can be unreliable)
naloxone
pure opioid antagonist

most commonly used opioid antagonist in vet med

parenteral use only (usually IV), slightly shorter acting than morphine
diprenorphine
pure opioid antagonist

parenteral only (usually IM)

used only to reverse etorphine-induced immobilization
naltrexone
pure opioid antagonist

uses:
control crib biting in horses
reverse carfentanil-induced immobilization

long duration of action
oral or parenteral use
butorphanol
mixed opioid agonist/antagonist

uses:
analgesic
antitussive
preanesthetic med
chemical restraint (w/ alpha-2 agonist)

popular in horses d/t low incidence of excitatory effects
weak resp. depression, less constipation
buprenorphine
mixed opioid agonist/antagonist

uses:
analgesic in dogs & cats
alternative to methadone for addicts

longer duration of action than torb, morphine
reverse w/ naloxone given PRIOR to buprenorphine
well tolerated in horses
loperamide
misc. opioid agent (=Immodium)

used to tx diarrhea

avoid repeated use --> constipation
can cause profound sedation in certain dog breeds (collies, Australian shepherds, etc.)
apomorphine
misc. opioid agents
strong dopaminergic agonist

emetic of choice in dogs
give conjunctivally (or SQ)
innovar
neuroleptanalgesic

= droperidol + fentanyl
midazolam + morphine
benzo/opioid combo

given IM as pre-med to dogs that can't be handled easily &/or are in pain
often given to cats as alternative to ketamine (ex. w/ intracranial mass, etc.)
diazepam + morphine
benzo/opioid combo

given IV as pre-med to calm depressed &/or sick dogs
neuroleptanalgesia
(+): sedation, dec. anxiety, intense analgesia, dec. movement, NO emesis, dec. dose of other drugs

(-): resp. depression, extrapyramidal effects, chest rigidity, change in autonomic fn
benzodiazepine/opioid combos
(+): sedation, dec. anxiety, intense analgesia, amnesia, minimal autonomic effects, NO extrapyramidal effects

(-): resp. depression (easily reversed w/ opioid antagonist)
determinants of tension of gas in alveoli (FA)
rate of delivery of gas TO alveoli:
1. tension of anesthetic gas in inspired gas (FI)
2. minute volume

rate of removal of gas FROM alveoli:
1. cardiac output
2. blood solubility (Fblood)*
blood solubility & induction/recovery
LOW blood solubility:
fast induction & recovery

HIGH blood solubility: slow induction & recovery
effects of inhalational anesthetics
all produce dose dependent depression of respiration & MAP
minimal skeletal muscle relaxation

halothane is most potent (lowest MAC)
sevo has fastest induction/recovery (lowest max vapor conc.)
cons of halothane
hypotension d/t dec. myocardial contractility
arrhythmias
significant hepatic biotransformation (hepatotoxic metabolites)

alters Ca++ movements
1. intearctions w/ aminoglycoside Abs, Ca channel blockers --> severe CV depression
2. can produce malignant hyperthermia (esp. in pigs), caused by failure of Ca uptake in SR
dantrolene sodium
used to tx malignant hyperthermia

decreases Ca++ release from SR
sevoflurane
hypotension d/t vasodilation, esp. in muscle & skin (same w/ iso)
unstable in soda lime
excellent for sea turtles
expensive
nitrous oxide
used as adjunct to anesthesia in small animals b/c:
1. concentration & 2nd gas effects
2. decreases dose of primary anesthetic
3. mild stimulation of symp. nervous system
4. ANALGESIC

avoid conc. > 70-75%
do not give to patients w/ any condition where air is trapped in viscera --> will cause air pocket to expand (ex. pneumothorax)
concentration effect
only seen w/ high conc. of nitrous oxide

when higher conc. of anesthetic gas is inhaled, FA (& therefore Fblood), inc. at a slightly greater rate than if a lesser conc. were inhaled
2nd gas effect
occurs when a 2nd gas (ex. 1% halothane) is inspired w/ 75% nitrous & 24% O2

conc. effect produced by 75% N2O not only concentrates O2, but also halothane --> inc. rate of movement of halothane from alveolar air to pulm. blood --> faster induction
uses of analeptics
used to reverse drug-induced CNS depression (esp. respiratory depression)

cause general CNS stimulation --> can result in convulsions
doxapram
most commonly used analeptic

used to stimulate respiration during or after gen. anesthesia, in newborns, in cases of cardiopulm. arrest

stimulates carotid & aortic chemoreceptors --> reflux stimulation of medullary resp. centers

short duration: 5-10 m.
excessive doses --> hypertension, hyperventilation, seizures (rare)
strychnine
analeptic; used as a pesticide

glycine receptor antagonist --> CNS stimulation

strychnine poisoning --> severe & extremely painful convulsions
theophylline
methylxanthine (weak analpetic)

used in tx of asthma, adjunct to digoxin to tx CHF (dilates coronary aa.)
aminophylline
methylxanthine (weak analpetic)

H2O sol. salt of theophylline (better oral absorption)

used in tx of asthma, adjunct to digoxin to tx CHF (dilates coronary aa.)
theobromine
methylxanthine (weak analpetic)

in chocolate
cocaine
local anesthetic (ester)

only one to cause vasoconstriction
proparacaine
local anesthetic (ester)

used to anesthetize cornea
lasts 15-30 m.
lidocaine
local anesthetic (amide)

most widely used local anesthetic

used to tx post-op ileus in horse

may cause local irritation & swelling, esp. in horse
bupivacaine
local anesthetic (amide)

useful for post-op analgesia
duration up to 8 hrs
mepivacaine
local anesthetic (amide)

most widely used local in horses b/c it causes little swelling & edema
mechanism of action of local anesthetics
block initiation & propagation of AP by preventing voltage-dep. inc. in Na permeability that accompanies a small inc. in mem depolarization
factors influencing sensitivity of nerves to blockade by local anesthetics
firing rate of nerve: resting Na channels least susceptible, then open channels, inactivated channels most susceptible

pH of body fluids & pKa of local anesthetic: uncharged mols penetrate mem, but CHARGED mols bind receptors (if pH dec. d/t inflammation --> more drug needed to block)

anatomical structure of nerve: small diameter n. easier to block
local anesthetics: determinants of absorption from site of administration
dosage
site of injection: absorbed more quickly in highly vascular area
extent of tissue binding: keeps drug at site of admin --> inc. duration of action
concurrent admin of vasoconstricting substances: locals are vasodilators & usually sold w/ vasoconstrictor (ex. epi); vasoconstriction --> inc. efficacy b/c systemic absorption is decreased d/t low blood flow
metabolism of local anesthetics
esters: shorter half life d/t rapid hydrolysis by plasma & liver cholinesterases
amides: hydrolyzed by liver microsomal enzymes (DO NOT USE w/ liver dz)
systemic effects of cocaine
restlessness, euphoria --> tremors --> convulsions

vasoconstriction, hypertension, arrhythmias
systemic effects of local anesthetics (except cocaine)
only w/ HIGH plasma levels:

marked hypotension d/t dec. cardiac contractility --> dec. CO & vasodilation by dec. symp. tone
mechanisms of action of seizures
seizure focus activated, seizure discharge from focal area may synchronize w/ other neurons & propagate to surrounding areas of brain

dec. GABA activity & inc. glutamate activity important
3 ways anticonvulsants inhibit seizures
1. dec. excessive discharge of seizure focus
2. inc. seizure threshold required for discharge
3. dec. spread of discharge to surrounding neurons

most drugs work by 2 & 3
tx for chronic seizures in dogs & cats
Dogs:
1. phenobarb
2. phenobarb + KBr
3. KBr alone

Cats:
1. phenobarb
2. benzodiazepine
3. third level drugs
when to start tx for seizures
> 1 seizure/month
very intense seizures w/ breathing difficulties
clusters of seizures
pros of phenobarbital for tx of seizures
effective against wide spectrum of epilepsies
inexpensive
relatively non-toxic
easy to measure blood levels
relatively little sedation
cons of phenobarbital for tx of seizures
polyphagia --> wt. gain
PU/PD
hepatotoxicity

w/ chronic use:
altered bone metabolism
inc. metabolism of other drugs using liver microsomal enzymes
blood dyscrasias
inc. liver enzymes
mechanism of action of phenobarb for tx seizures
inc. seizure threshold, dec. spread of discharge d/t facilitation of GABA, then also inhibition of glutamate

at higher doses, may dec. Ca flux across neuronal mem
primidone
anticonvulsant (dogs only)

congener of phenobarb
more expensive, more hepatotoxic, quite sedative intially

it & 2 metabs all anti-convulsant
benzodiazepines to tx seizures
orally ineffective in dogs
tolerance to anticonvulsant properties can develop over time
most potent elevator of seizure threshold: facilitates GABA

diazepam: used in cats that are refractory to phenobarb (don't give orally)

clonazepam: not metab. by liver microsomal enzymes (no active metabolites), longer half life, doesn't cause hepatic necrosis
cons of potassium bromide
vomiting
pancreatitis (rare)
takes ~1 mo. to reach therapeutical plasma levels
in emergency, would have to give large loading dose --> potentially cardiotoxic (can use sodium bromide IV instead)
third level drugs used to tx seizures
felbamate (dogs)
gabapentin (dogs, cats)
tx of status epilepticus
1. IV diazepam (2-3 doses if needed)
2. IV phenobarbital
3. if still seizing, IV pentobarbital to produce anesthesia (or IV propofol)

if seizures result of strychnine poisoning: tx of choice is anesthetic dose of IV pentobarbital
cons of propofol
-some pain w/ IV administration
-can damage tissue if given extravascularly
-apnea common after administration
-dose dependent vasodilation --> dec. MAP (do NOT use in hypotensive patients)
-cats: chronic admin can cause oxidative injury to RBCs