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113 Cards in this Set
- Front
- Back
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barbiturates
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phenobarbital
pentobarbital methohexital thiopental thiamylal |
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alpha-2 agonists
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xylazine
medetomidine detomidine |
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benzodiazepines
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diazepam
clonazepam zolazepam midazolam |
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dissociative anesthetics
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ketamine
tiletamine |
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neuroleptics
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phenothiazines: acepromazine, chlorpromazine
butyrophenones: droperidol |
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pure opioid agonists
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morphine
hydromorphone (oxymorphone) etorphine codeine dextromethorphan methadone carfentanil sufentanil fentanyl |
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pure opioid antagonists
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naloxone
naltrexone diprenorphine |
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mixed opioid agonists/antagonists
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butorphanol
buprenorphine |
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miscellaneous opioids
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loperamide
apomorphine |
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inhalational anesthesetics
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halothane
isoflurane sevoflurane nitrous oxide |
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analeptics
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doxapram
strychnine theophylline aminophylline theobromine |
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local anesthetics
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esters: cocaine, proparacaine
amides: lidocaine, bupivacaine, mepivacaine |
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anticonvulsants
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phenobarbital
primidone diazepam clonazepam potassium bromide felbamate gabapentin |
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phenobarbital
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barbiturate
used to tx seizure disorders in dogs & cats; occasionally used as oral sedative |
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pentobarbital
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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) |
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thiopental
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barbiturate
ultra short acting excellent IV induction agent in young, healthy animals, or alone for very short procedures |
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thiamylal
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barbiturate
ultra short acting no longer available in US; replaced by thiopental |
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methohexital
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barbiturate
ultra-short acting anesthetic agent often used in sight hounds b/c it does not depend on redistribution to fat to reverse effect |
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etomidate
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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) |
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propofol: facts + pros
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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 |
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barbiturates & lipid solubility
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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 |
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barbiturates: metabolism & redistribution
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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 |
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clinical uses of barbiturates
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induction
tx of seizures to decrease ICP & tx cerebral edema euthanasia |
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cons of barbiturates
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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) |
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CV, resp. effects of barbiturates
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brief hypotension, reflex tachycardia
transient resp. depression (+/- apnea) arrhythmias, esp. in excited animals |
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clinical uses of alpha-2 agonists
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preanesthetic agent
chemical restraint selectivity: xylazine < detomidine < medetomidine duration: detomidine longest |
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effects of alpha-2 agonists
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increases potency of other anasthetic drugs
sedation/hypnosis analgesia muscle relaxation |
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adverse effects of alpha-2 agonists
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emesis
resp. depression CV effects (vary b'twn drugs) bloat hyperglycemia increased urine output don't use xylazine during last mo. of pregnancy |
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CV effects of xylazine
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transient hypertension followed by prolonged hypotension
bradycardia arrhythmias |
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clinical uses of guaifenesin
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adjunct to anesthesia in horses (IV)
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effects of guaifenesin
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sedation/hypnosis
analgesia muscle relaxation antipyretic antitussive |
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pros & cons of guifenesin
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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) |
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clinical uses of benzodiazepines
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pre-anesthetic med (often w/ opioids)
tx of seizures (midazolam: neonatal seizures in foals) tx anorexia in cats tx fears & phobias |
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pros of benzodiazepines
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dec. dose of other anesthetic drugs
muscle relaxant weak resp. depression minor CV effects |
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cons of benzodiazepines
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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 |
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pharmacokinetics of benzodiazepines
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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 |
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mechanism of action of benzodiazpines
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facilitates GABA by binding to site on GABA receptor --> inc. affinity of GABA for receptor & vice versa --> GABA produces inc. in chloride conductance
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flumazenil
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benzodiazepine receptor antagonist
useful in sick animals, esp. cats, to speed up recovery from anesthesia |
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mechanism of action of barbiturates
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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 |
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dissociative anesthetic state
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eyes open
involuntary movements vocalization hallucinations feel separated from body |
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physiological effects of dissociatives
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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 |
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mechanism of acation of dissociatives
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noncompetitive antagonists of NMDA glutamate receptor --> inc. activity of layer V pyramidal output neurons (that release glutamate) --> disruption of thalamic & cerebral functions
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tiletamine
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similar to ketamine, but longer duration of action
can only be bought mixed w/ benzo zolazepam = Telazol (recoveries may be prolonged & rough) |
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clinical uses of neuroleptics
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chemical restraint
preanesthetic meds (dec. dose of other meds) antiemetic |
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neuroleptic syndrome
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sedation
tranquilization dec. emotional behavior dec. responsiveness to external stimuli dec. spontaneous movement NOT hypnotic NO analgesia alone |
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adverse effects of neurolpetics
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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 |
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mechanism of action of neuroleptics
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antagonize dopaminergic, alpha-adrenergic, muscarinic, H1, certain serotonergic receptors
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phenothiazine neuroleptics: effects in horses
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ace, chlorpromazine
can cause violent incoordination & excitement penile prolapse & priapism |
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droperidol
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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 |
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mechanism of action of opioids & opiopeptins
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decrease release of substance P --> dec. transmission of nociceptive info
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species dependent effects of morphine
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dogs, monkey, man: analgesia, sedation, euphoria, pupillary miosis
horses, cats, pigs, ruminants: analgesia, excitement, dysphoria, mydriasis (use low doses) |
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pros of morphine
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valuable premed b/c dec. amt. of other drugs
antitussive mild hypotension, bradycardia |
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cons of morphine
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dose dependent resp. depression: CAUTION w/ lung dz, neonates
constipation, esp. w/ chronic use emetic SEVERE hypotension if in shock or w/ volume depletion |
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hydromorphone
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pure opioid agonist
similar to morphine, but 5x more potent less GI upset & vomiting than morphine in dogs |
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etorphine
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pure opioid agonist
agonist at all receptors, 1000x more potent than morphine used only to immobilize wild animals |
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codeine
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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 |
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dextromethorphan
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pure opioid agonist
devoid of all opioid properties except ANTITUSSIVE effect |
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meperidine
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pure opioid agonist (=Demerol)
effective analgesic, maintains much of potency when given PO less constipating than morphine |
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methadone
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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 |
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carfentanil
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pure opioid agonist
most potent of fentanil family (all are short acting, w/ rapid onset) used to immobilize wild animals |
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sufentanil
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pure opioid agonist
anesthetic adjunct in dogs |
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fentanyl
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pure opioid agonist
anesthetic adjunct in dogs patches: control of chronic pain (absorption can be unreliable) |
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naloxone
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pure opioid antagonist
most commonly used opioid antagonist in vet med parenteral use only (usually IV), slightly shorter acting than morphine |
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diprenorphine
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pure opioid antagonist
parenteral only (usually IM) used only to reverse etorphine-induced immobilization |
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naltrexone
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pure opioid antagonist
uses: control crib biting in horses reverse carfentanil-induced immobilization long duration of action oral or parenteral use |
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butorphanol
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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 |
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buprenorphine
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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 |
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loperamide
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misc. opioid agent (=Immodium)
used to tx diarrhea avoid repeated use --> constipation can cause profound sedation in certain dog breeds (collies, Australian shepherds, etc.) |
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apomorphine
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misc. opioid agents
strong dopaminergic agonist emetic of choice in dogs give conjunctivally (or SQ) |
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innovar
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neuroleptanalgesic
= droperidol + fentanyl |
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midazolam + morphine
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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.) |
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diazepam + morphine
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benzo/opioid combo
given IV as pre-med to calm depressed &/or sick dogs |
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neuroleptanalgesia
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(+): sedation, dec. anxiety, intense analgesia, dec. movement, NO emesis, dec. dose of other drugs
(-): resp. depression, extrapyramidal effects, chest rigidity, change in autonomic fn |
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benzodiazepine/opioid combos
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(+): sedation, dec. anxiety, intense analgesia, amnesia, minimal autonomic effects, NO extrapyramidal effects
(-): resp. depression (easily reversed w/ opioid antagonist) |
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determinants of tension of gas in alveoli (FA)
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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)* |
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blood solubility & induction/recovery
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LOW blood solubility:
fast induction & recovery HIGH blood solubility: slow induction & recovery |
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effects of inhalational anesthetics
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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.) |
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cons of halothane
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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 |
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dantrolene sodium
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used to tx malignant hyperthermia
decreases Ca++ release from SR |
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sevoflurane
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hypotension d/t vasodilation, esp. in muscle & skin (same w/ iso)
unstable in soda lime excellent for sea turtles expensive |
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nitrous oxide
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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) |
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concentration effect
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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 |
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2nd gas effect
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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 |
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uses of analeptics
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used to reverse drug-induced CNS depression (esp. respiratory depression)
cause general CNS stimulation --> can result in convulsions |
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doxapram
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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) |
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strychnine
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analeptic; used as a pesticide
glycine receptor antagonist --> CNS stimulation strychnine poisoning --> severe & extremely painful convulsions |
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theophylline
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methylxanthine (weak analpetic)
used in tx of asthma, adjunct to digoxin to tx CHF (dilates coronary aa.) |
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aminophylline
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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.) |
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theobromine
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methylxanthine (weak analpetic)
in chocolate |
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cocaine
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local anesthetic (ester)
only one to cause vasoconstriction |
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proparacaine
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local anesthetic (ester)
used to anesthetize cornea lasts 15-30 m. |
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lidocaine
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local anesthetic (amide)
most widely used local anesthetic used to tx post-op ileus in horse may cause local irritation & swelling, esp. in horse |
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bupivacaine
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local anesthetic (amide)
useful for post-op analgesia duration up to 8 hrs |
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mepivacaine
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local anesthetic (amide)
most widely used local in horses b/c it causes little swelling & edema |
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mechanism of action of local anesthetics
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block initiation & propagation of AP by preventing voltage-dep. inc. in Na permeability that accompanies a small inc. in mem depolarization
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factors influencing sensitivity of nerves to blockade by local anesthetics
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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 |
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local anesthetics: determinants of absorption from site of administration
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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 |
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metabolism of local anesthetics
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esters: shorter half life d/t rapid hydrolysis by plasma & liver cholinesterases
amides: hydrolyzed by liver microsomal enzymes (DO NOT USE w/ liver dz) |
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systemic effects of cocaine
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restlessness, euphoria --> tremors --> convulsions
vasoconstriction, hypertension, arrhythmias |
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systemic effects of local anesthetics (except cocaine)
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only w/ HIGH plasma levels:
marked hypotension d/t dec. cardiac contractility --> dec. CO & vasodilation by dec. symp. tone |
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mechanisms of action of seizures
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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 |
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3 ways anticonvulsants inhibit seizures
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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 |
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tx for chronic seizures in dogs & cats
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Dogs:
1. phenobarb 2. phenobarb + KBr 3. KBr alone Cats: 1. phenobarb 2. benzodiazepine 3. third level drugs |
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when to start tx for seizures
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> 1 seizure/month
very intense seizures w/ breathing difficulties clusters of seizures |
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pros of phenobarbital for tx of seizures
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effective against wide spectrum of epilepsies
inexpensive relatively non-toxic easy to measure blood levels relatively little sedation |
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cons of phenobarbital for tx of seizures
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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 |
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mechanism of action of phenobarb for tx seizures
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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 |
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primidone
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anticonvulsant (dogs only)
congener of phenobarb more expensive, more hepatotoxic, quite sedative intially it & 2 metabs all anti-convulsant |
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benzodiazepines to tx seizures
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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 |
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cons of potassium bromide
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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) |
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third level drugs used to tx seizures
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felbamate (dogs)
gabapentin (dogs, cats) |
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tx of status epilepticus
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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 |
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cons of propofol
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-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 |
