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Anesthesia & Analgesia > Drugs > Flashcards

Drugs Flashcards

1
Q

What kind of drug is a phenothiazine? What kind of phenothiazine do we use?

A

Pre-anesthetic medication
Acepromazine

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2
Q

What are the actions of phenothiazines?

A
  • anti-adrenergic (a1 blocker), antidopaminergic, anticholinergic (muscarine blocker), antihistaminic (H1 blocker), antiserotonergic (5-HT blocker), local anesthetic effects (ion channel blockade), anti-arrhythmic, NO ANALGESIA, anti-thrombotic actions
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3
Q

What are the effects of phenothiazines?

A
  • sedation, hypotension, hypothermia, anti-emetic, anti-arrhythmic
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4
Q

What is the pharmacology of phenothiazines?

A
  • contain 2 benzene rings that are linked by a sulphur & nitrogen atom
  • highly protein bound (>90%)
  • lipophilic - cross the BBB & placenta
  • hepatic metabolism
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5
Q

What are the phenothiazines’ wide variety of actions?

A

primarily depress parts of the CNS which assist in the control of homeostasis:
- vasomotor control, thermoregulation, hormonal balance, acid-base balance, emesis

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6
Q

What are the mechanisms of action of phenothiazines?

A
  • mental calming effect - mediated by ANTIDOPAMINERGIC actions in the CNS
  • useful to calm, seem to reduce anxiety, anesthetic sparing
  • overdose of these drugs will cause catalepsy
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7
Q

What are the negative side effects of phenothiazines?

A
  • CARDIOVASCULAR effects: HYPOTENSION through vascular smooth muscle A1 receptor blockade
  • RESPIRATORY effects: reduces the sensitivity of the respiratory center to CO2
  • THERMOREGULATORY effects: hypothermia can occur due to disruption of thermoregulation & cutaneous vasodilation
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8
Q

What are the positive side effects of phenothiazines?

A
  • ANTI-EMETIC: effect in central chemoreceptor trigger zone
  • ANTI-ARRHYTHMIC: increases the concentration of epinephrine required to induce cardiac arrhythmias
  • ANTI-HISTAMINE: contraindicated prior to allergy testing/skin biopsies
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9
Q

What is acepromazine?

A
  • commonly used in vet med - calming effect
  • 30-40% anesthetic sparing effect
  • mild sedation when used alone, NO ANALGESIA
  • commonly combined w/ A2-agonists, opioids
  • used in cats, dogs, HORSES (do not use in breeding stallions - have been rare cases of penile prolapse), rarely used in Ru or exotics
  • can be used in seizure prone animals
  • can also be used for controlling emergence delirium during recovery from anesthesia
  • solution is yellow in colour
  • slow time to onset of effect, even after IV administration
  • dose-dependent (duration & severity of side effects - HYPOTENSION)
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10
Q

What kind of drugs are benzodiazepines?

A

pre-anesthetic medication

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11
Q

What are benzodiazepines?

A
  • ANTICONVULSANT
  • AVOID using ALONE IV in Ca, Fe, Eq (EXCITEMENT possible in young, healthy animals; may become AGGRESSIVE)
  • better combined w/ mu-opioids (IV or IM - combination good in SICK, OBTUNDED dogs)
  • sedation when used for exotic animals
  • reduces amount of major anesthetic (anesthetic sparing)
  • muscle relaxation
  • retrograde amnesia
  • NO ANALGESIA
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12
Q

What is the pharmacology of benzodiazepines?

A
  • consist of benzene rings fused to a diazepine ring
  • well absorbed across mucous membranes
  • significant first-pass metabolism if administered orally - need to increase dose
  • highly protein bound (>95%)
  • hepatic metabolism - oxidation & conjugation
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13
Q

What are the mechanisms of action of Benzodiazepines?

A
  • act on specific benzodiazepine binding sites - which are associated w/ GABA(A) receptors
  • depresses activity in reticular activating system, by enhancing GABA actions -> ANXIOLYSIS & SEDATION (dose dependent) - SEDATION IS UNRELIABLE IN SOME ANIMALS - CAN CAUSE EXCITMENT
  • central GABA - enhancing activity -> ANTI-CONVULSANT effect
  • act in the spinal cord - depress internuncial transmission -> MUSCLE RELAXATION
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14
Q

What are the side effects of benzodiazepines?

A
  • minimal CARDIOVASCULAR effects
  • minimal RESPIRATORY effects
  • CNS depression: overdose can cause coma
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15
Q

What drugs are benzodiazepines?

A
  • diazepam
  • midazolam
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16
Q

What is important about diazepam?

A
  • adheres to plastic syringes (takes up to 12 hrs)
  • sensitive to light degradation
  • propylene glycol carrier (pH 6.8): painful on IM injection & unreliable absorption
  • active metabolites - Nordiazepam
  • crosses placenta, reaches fetus, & remains in fetus: DO NOT use for c-sections unless antagonist (flumazenil) is available
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17
Q

What is important about midazolam?

A
  • contains an imidazole ring: in acidic solution (pH < 4), ring opens & cmpd is water soluble; pH > 4, ring closes & cmpd becomes highly LIPOPHILIC
  • can be administered IM, intranasal, transmucosal
  • 2-3x more potent than diazepam
  • inactive metabolites
  • popular in EXOTIC ANESTHESIA (reliable sedation)
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18
Q

What is important about flumazenil?

A

Benzodiazepine ANTAGONIST at benzodiazepine binding site on GABA(A) receptor
- no side effects
- increases muscle tone to normal - improves ventilation
- useful for exotic animal anesthesia
- 30-60 mins duration IV, IM

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19
Q

What drugs are behaviour modifiers?

A
  • Trazadone
  • Gabapentin
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20
Q

What is important about trazadone?

A
  • serotonin receptor antagonist & reuptake inhibitor
  • some A1 receptor blocking action - possible hypotension
  • oral administration, may be given before visit
  • similar to using acepromazine to decrease stress
  • can be combined w/ opioid
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21
Q

What is important about gabapentin?

A
  • mechanism underlying its anxiolytic properties is unclear
  • has an inhibitory effect on voltage gated calcium channels in neural tissue decreasing the release of glutamate w/in the CNS
  • routinely used for treatment of chronic pain & epilepsy
  • oral administration may be given before visit
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22
Q

What are the different injectable anesthetics?

A
  1. propofol
  2. alfaxalone
  3. ketamine
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23
Q

What is important about propofol?

A
  • acts on GABA(A) receptors in CNS to produce anesthesia
  • induction smooth & rapid: onset 40-90 secs & 1 dose last 5-10 mins
  • short duration of action depends on REDISTRIBUTION: EXTRA-HEPATIC sites of metabolism - kidneys, lungs, GI tract
  • recovery fast & smooth
  • used for induction & maintenance (TIVA)
  • no analgesia
  • occasionally pain upon IV injection
  • no tissue damage if injected perivascular
  • vehicle is a lipid emulsion (‘Intralipid)
  • PropoClear - lipid free formulation
  • Propoflo 28 - contains preservative & is labelled for use up to 28 days after opening
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24
Q

What effects does propofol have on the cardiovascular system?

A
  • cardiovascular depression is DOSE DEPENDENT
  • myocardial depression
  • venodilation - decreased BP
  • resets baroreceptor reflex - increase in HR w/ drop in BP does NOT occur
  • AVOID IN hypovolemic animals & patients w/ cardiac disease
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25
Q

What effects does propofol have on the respiratory system?

A
  • respiratory depression is DOSE DEPENDENT
  • post-induction apnea
  • post-induction cyanosis
  • supplement oxygen & pre-oxygenate
  • mild bronchodilation
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26
Q

What effects can you occasionally get on induction &/or recovery with propofol?

A
  • dogs: limb stiffness, paddling movements, opisthotonos, twitching
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27
Q

what is propofol recommended for?

A
  • C-SECTIONS
  • CEREBROPROTECTION: reduces CBF & cerebral metabolic rate
  • patients w/ compromised LIVER function
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28
Q

What is important about propofol in Fe?

A
  • reduced capacity for glucuronide conjugation
  • propofol infusion (recovery from anesthesia delayed)
  • repeated administration over several days: hemolysis & Heinz Body formation; clinical relevance has been questioned
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29
Q

What is important about alfaxalone?

A
  • acts on GABA(A) receptors to CNS to produce anesthesia
  • induction smooth & rapid: onset 15-45 secs & 1 dose lasts 5-10 mins
  • short duration of action depends on REDISTRIBUTION
  • recovery fast, quality improves w/ premedication
  • used for induction & maintenance (TIVA) - rapidly metabolized
  • no analgesia
  • no pain upon injection
  • no tissue damage if injected perivascular
  • similar effects to Propofol
  • can be administered IM
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30
Q

How does alfaxalone effect the cardiovascular system?

A
  • cardiovascular depression is DOSE DEPENDENT
  • hypotension (combination of myocardial depression & some peripheral vasodilation)
  • compensation via reflex tachycardia (Baroreceptor reflex)
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31
Q

How does alfaxalone effect the respiratory system?

A
  • respiratory depression is DOSE DEPENDENT
  • post-induction apnea
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32
Q

What is alfaxalone good for?

A
  • good muscle relaxation
  • produces reliable sedation when given IM in cats
  • excellent in reptiles (IM)
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33
Q

How does co-induction of another drug with alfaxalone or propofol work?

A
  • combine alfaxalone OR propofol w/ another agent to minimize the amount required
  • typical agents used include (Benzodiazepines (Midazolam or Diazepam); ketamine)
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34
Q

what is ketamine?

A
  • DISSOCIATIVE ANESTHETIC AGENT - interrupts information reaching higher centers in the brain
  • different from GABA(A) agonist drugs: cataleptoid state w/ slow nystagmus; muscle rigidity w/ higher doses; maintains cranial nerve reflexes - gag, swallow, palpebral, & central eye in dogs & cats (no ventral-medial rotation)
  • racemic mixture (S(+)isomer is 2-4x more potent
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35
Q

What is important about ketamine?

A
  • popular in vet med (high margin of safety)
  • slow onset (30-90 sec) & longer duration (20-30 mins)
  • USED FOR INDUCTION & MAINTAENANCE & ANALGESIA - will accumulate
  • can be administered: IM, IV, SC, TM
  • profound ANALGESIA (somatic > visceral; wind up pain (NMDA antagonist))
  • sub-anesthetic doses can be used for reliable SEDATION
  • neither anti- nor pro-convulsant
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36
Q

What are the mechanisms of action of ketamine?

A
  • NMDA receptor antagonist - analgesic effects
  • CNS voltage dependent Na+, K+, Ca2+ channels
  • depression of CNS Acetyl Choline receptors
  • some action at GABA(A) receptors
  • depression of nociceptive cells in the dorsal horn of the spinal cord
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37
Q

Side effects of ketamine?

A
  • muscle rigidity (catatonia): ALWAYS combine w/ muscle relaxant (benzodiazepine or a2-agonist)
  • AVOID in CATS w/ compromised renal function
  • auditory & visual stimuli disturbed during recovery can cause ‘emergence delirium’
  • USE W/ OTHER DRUGS TO REDUCE SIDE-EFFECTS (benzodiazepines, A2-agonists, acepromazine)
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38
Q

How does ketamine affect the cardiovascular system?

A

healthy animals: indirect mild cardiovascular stimulation
- sympathomimetic effects last for 2-15 mins
- increase in cardiac work & myocardial oxygen consumption
- AVOID IN CATS w/ hypertrophic cardiomyopathy

Critically ill patients OR catecholamine depleted:
- may see mild direct myocardial depressant effects

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39
Q

How does ketamine affect the respiratory system?

A
  • minimal respiratory depression
  • bronchodilation
  • laryngeal & pharyngeal reflexes are preserved
  • irregular/periodic breathing pattern - apneustic breathing
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40
Q

Does ketamine cause behavioural side effects?

A
  • can cause rough recoveries (head shaking, vocalization, dysphoria, salivation)
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41
Q

Why do we combine ketamine with other drugs?

A
  • decrease the amount of ketamine needed
  • eliminate unwanted side effects (improve recovery quality)
  • produce good skeletal muscle relaxation
  • improve visceral analgesia
  • prolong the period of anesthesia/ immobilization
42
Q

What is important about Ket-Val?

A

Ketamine/Diazepam
- IV induction agent in: Dogs, cats, neonatal foals, horses, calves, & cattle
- slow onset (30-90 sec)
- short acting, rapid recovery
- MINIMAL CARDIOVASCULAR SIDE EFFECTS
- MINIMAL RESPIRATORY SIDE EFFECTS
- DO NOT USE FOR C-SECTIONS (diazepam accumulates in neonates)
- less side effects than A2/ketamine

43
Q

What are our options for combining an A2-agonist w/ ketamine?

A
  • xylazine + ketamine
  • dexmedetomidine + ketamine + opioid
44
Q

What is important about xylazine + ketamine?

A
  • good combination in large animals (horse, cattle) (IV)
  • reliable for wildlife immobilization (IM)
  • analgesia, muscle relaxation, & narcosis
  • potent cardiopulmonary depression
  • not recommended for routine use in cats & dogs
45
Q

What is important about Dexmedetomidine + ketamine + opioid?

A
  • “kitty-magic”
  • wildlife, game ranch animals
  • supportive care (provide oxygen)
  • monitor closely
  • A2 reversible (Atipamezole)
46
Q

What are our A2 Agonists?

A
  • are NOT pure A2 agonists
  • newer A2 agonists have more specific action on the A2, & less action on the A1 receptors
  • xylazine (Anased, Rompun)
  • clonidine
  • detomidine (Dormosedan)
  • romifidine (Sedivet)
  • medetomidine (Domitor)
  • dexmedetomidine (Dexdomitor)
47
Q

What are our A2 Antagonists?

A
  • Atipamezole
  • Yohimbine
    -Tolazoline
48
Q

What is important about Atipamezole?

A
  • most selective A2 antagonist available
  • competitive antagonist
  • occasionally accompanied by: muscle tremors, tachycardia, over-alertness, transient hypotension, panting, defecation vomiting
  • reversal of both sedation & ANALGESIA
  • only labelled for IM administration
49
Q

What is important about Yohimbine?

A

more of a historical drug
- general CNS stimulant w/ antagonist action at the A2 receptors
- tachycardia is possible
- used for xylazine (Eq, Ca, Fe)
- not in cattle (volume is too large)

50
Q

What is important about Tolazoline?

A

more of a historical drug
- true A2 receptor antagonist
- more suitable volume in cattle
- can cause excitement when administered IV

51
Q

What is the A2 agonist of choice for SMALL ANIMAL premed?

A

Dexmedetomidine

52
Q

What is important about Dexmedetomidine?

A
  • Highly selective for the A2 receptor
  • IM in dogs & cats
  • excellent sedative for healthy exotics
  • always combine w/ an opioid for more reliable results
  • if IV administration, decrease dose by half
  • quality of sedation is profound but can override
  • dose dependent CV & respiratory depression (choose your dose based on a number of factors: patient temperament, hydration status, anticipated pain level of the procedure)
  • onset of action: 15 mins
  • duration of action: 45 mins - 1 hr
  • reversal available - Atipamezole
53
Q

What is the A2 agonist used in Eq, Ru, & camelid premed?

A

xylazine

54
Q

What is important about Xylazine?

A
  • Eq & Ru IV, camelid IM
  • excellent sedative in healthy patients
  • quality of sedation is excellent
  • reflex bradycardia is profound but transient
  • onset of action: minutes
  • duration of action: 30-45 mins
  • can be reversed if necessary (RARE)
55
Q

What is the A2 agonist used mainly in Eq for premed?

A

Detomidine

56
Q

What is important about Detomidine?

A
  • IV or IM in Eq
  • good quality sedation (may be slightly more ataxic/depressed than w/ xylazine)
  • onset & duration of action similar to xylazine
57
Q

What do we use for sedation for minor procedures in small animals?

A

dexmedetomidine
- provides profound sedation for minor procedures: quill removal, laceration repair
- combine w/ an opioid to improve quality of sedation
- combine w/ local block if possible
- IV to effect
- sedation even more profound if administered IV - place a catheter so “top ups” are more easily administered
- reversible - get rid of drugs once procedure is complete

58
Q

What do we use for sedation for standing procedures in large animals?

A
  • xylazine
  • detomidine
59
Q

Xylazine for standing procedures?

A

xylazine

Eq
- teeth floats, minor lacerations
- feet firmly planted but can still kick so be aware
- often combined w/ butorphanol
- IV

Bo
- foot trims
- IM
- combine w/ butorphanol IM
- will result in recumbency in 15 mins
- duration of action ~60mins
- reverse w/ Tolazoline (IM to avoid excitement)

60
Q

Detomidine for standing procedures?

A
  • often combined w/ an opioid (butorphanol) for standing procedures
  • for longer standing procedures, make up an infusion & administer to effect
61
Q

What works well as an infusion during surgery?

A

Dexmedetomidine
- anesthetic sparing & analgesia
- Ca: LD + VRI IV
- Eq: IV (no loading dose necessary)
- be aware of bradycardia w/ bolus
- more effective when combined w/ an opioid infusion (fentanyl/remifentanil)
- not commonly administered to cats as an infusion

62
Q

What should you use an an infusion in the post-operative period?

A

Dexmedetomidine
- benefits: analgesia & sedation
- indications: anxious dogs that need to be kept calm; fractious dogs that need to be in the ICU for post-operative care & handling; painful dogs that require something more than an opioid
- IV

63
Q

Why would you add dexmedetomidine to a local anesthetic?

A
  • prolongs duration of block
  • mix w/ local anesthetic & administer in the same syringe
  • some systemic uptake so may see increased levels of sedation
  • amt is v sm
  • need to dilute concentration of dexmedetomidine
  • mech of action: vasoconstriction associated w/ the A2 agonist delays clearance of local anesthetic from the site
64
Q

Dexmedetomidine in epidurals for small animals?

A
  • not routinely used
  • direct neurotoxic effects have not been fully tested
65
Q

Dexmedetomidine in epidurals for large animals?

A
  • prolongs duration of blockade
  • easily accessible for practitioners
  • does not produce motor blockade
  • often combined w/ other drugs: local anesthetics (lidocaine); opioids
  • produce analgesia (action on receptors in the substantia gelatinosa of the dorsal horn of the spinal cord)
  • adverse effects (ataxia, recumbency): can be reversed
  • systemic absorption occurs (CAUTION)
66
Q

What drugs do we use in epidurals for Eq?

A
  • xylazine
  • detomidine
  • romifidine
67
Q

xylazine in horse epidural?

A
  • provide 2.5 hrs of perineal analgesia
  • no HL ataxia
  • 1/5th the dose typically given systemically for sedation of Eq
  • dilute in saline or lidocaine for injection

if combining w/ lidocaine, do not exceed 10 mL
- higher vol you put in, the further up you are going to block (dont want them going down)

68
Q

detomidine in horse epidural?

A
  • potent analgesic & sedative effects
  • sedation, ataxia, recumbency, & CV effects can occur
  • use low doses
  • dilute in saline
  • analgesia will spread cranially (T14)
  • duration of analgesia shorter than xylazine (2 hrs)
  • diuresis occurs (contraindicated in Eq w/ urinary obstruction)
69
Q

romifidine in horse epidural?

A
  • diluted in saline
  • analgesia inconsistent (if it works, can provide up to 4 hrs of analgesia)
  • spreads cranially, similar to detomidine
  • sedation, bradycardia, & decreased RR has been reported
70
Q

What drugs do we use in epidurals for cattle?

A
  • xylazine alone
  • xylazine combined w/ lidocaine
  • romifidine
71
Q

xylazine epidural for cattle?

A
  • diluted in saline
  • onset of action: 10 mins
  • duration of action: 3-4 hr
72
Q

xylazine + lidocaine epidural for cattle?

A
  • onset of action: 5 mins
  • duration of action: 6 hr
73
Q

Side effects of xylazine epidurals in cattle?

A
  • mild to moderate sedation
  • mild ataxia
  • decreased ruminal motility
  • bradycardia
74
Q

romifidine epidural for cattle?

A
  • diluted in sterile saline
  • analgesia & sedative effect was dose dependent in intensity & duration of action
75
Q

What are the opioid antagonists?

A
  • naloxone
  • naltrexone
76
Q

What is important about naloxone?

A
  • pure mu, delta, kappa opioid antagonist
  • can reverse all opioid agonist effects (respiratory depression, sedation, dysphoria) producing increased: alertness, responsiveness, coordination, perception of pain
  • duration of action: 30-60 mins
  • watch for renarcotization
77
Q

What is important about naltrexone?

A
  • clinical effects last approximately 2x as long as those of naloxone
  • vet med: reversal of potent opioids for wildlife immobilization
78
Q

What should you use to reverse a mu-opioid induced respiratory depression?

A

Butorphanol
- mu-antagonist
- kappa-agonist
- maintains analgesia (kappa)

  • mu-opioid agonist: respiratory depression & sedation
79
Q

What are the opioid agonists & their relative potencies?

A

potency is compared to morphine on an “equal-analgesic basis”
- morphine (1)
- meperidine (1/5)
- fentanyl (100)
- carfentanil (10000)
- buprenorphine (80)
- butorphanol (3-5)

80
Q

Efficacy and Duration of the different opioids?

A
  • mild & short: meperidine
  • profound & long: morphine, hydromorphone, methadone
  • odd ones: buprenorphine (moderate effect & long duration), fentanyl, sufentanil (profound effect & short duration)
81
Q

Which opioid is given OTM (buccal)?

A

Buprenorphine

82
Q

What is important about buprenorphine?

A
  • Fe: acceptable bioavailability & analgesia
  • Ca: high dose required (cost prohibitive, risk of swallowing)
  • in clinical setting, IV or IM route provide better analgesia
  • suitable for late postoperative analgesia
83
Q

Which opioids do we administer transdermally?

A
  • fentanyl patch
  • transdermal fentanyl solution (Recuvyra)
84
Q

what is important about a fentanyl patch?

A
  • human safety considerations (should potentially not send home with O)
  • patch technology evolved to reduce potential for abuse (was a reservoir (filled w/ liquid), now drug in an adhesive matrix (active drug mixed w/ polymer)
  • spp differences in how skin affects drug movement
  • lower bioavailability in Fe
  • delayed onset (peak plasma concentration) - Ca: 12-24 hr (duration 3 days); Fe: 8-18 hr (duration up to 5 days)
85
Q

Why do you need to continue pain assessment & monitoring during transdermal opioid administration?

A
  • great individual variability in drug absorption
  • changes in BODY TEMP, SKIN PREP, & PATCH PLACEMENT may affect rate of absorption, plasma fentanyl levels, & analgesic efficacy substantially
  • care w/ heating pads (increased circulation increases uptake)
86
Q

What is important about transdermal fentanyl solution (Recuvyra)?

A
  • licensed for the control of postoperative pain associated w/ major orthopedic & soft tissue surgery in healthy dogs
  • only in USA
  • liquid solution applied to skin dorsally btwn shoulder blades (depot of fentanyl w/in lipid layer of the stratum corneum)
  • no needle necessary
  • requires risk training
  • applied 2-4 hrs prior to surgery
  • lasts for up to 4 days in dogs
  • no peak effect
  • adverse effects are long lasting (require repeated doses of naloxone)
87
Q

How are opioids administered spinally/epidurally?

A
  • often used in epidural or subarachnoid space to manage acute or chronic pain
  • all opioids are lipid soluble but solubility differs btwn opioids

opioids w/ lower lipid solubility
- less systemic absorption
- slower onset time (passage across dura mater)
- longer duration & further cranial migration: morphine 12-24 hrs, hydromorphone 8 hrs, fentanyl: short duration & segmental analgesia

88
Q

How are opioids administered intraarticularly?

A
  • significant increase in mu-opioid receptors in articular & peri-articular tissues occurs after joint inflammation
  • intra-articular administration of morphine after arthroscopy surgery (knee, elbow) as part of multimodal analgesia plan
89
Q

Who are the full mu-agonists?

A
  • superior analgesics
  • treatment of moderate to severe pain
  1. morphine
  2. hydromorphone
  3. methadone
  4. fentanyl
  5. meperidine
  6. sufentanil, alfentanil, remifentanil
90
Q

what is important about morphine?

A
  • full mu opioid agonist
  • ‘gold standard’ opioid to which others are compared, analgesia ++ to +++
  • histamine release if administered IV (hypotension)
  • vomiting
  • can also be administered neuraxially & intra-articularly
91
Q

What is morphine-6-glucaronide?

A
  • active metabolite (650x as potent as morphine)
  • pharmacological activities indistinguishable from morphine
  • contributes significantly to clinical analgesia w/ chronic morphine administration
92
Q

What is morphine-3-glucaronide?

A
  • little affinity for opioid receptors
  • may contribute to the EXCITATORY effects of morphine
93
Q

What is important about hydromorphone?

A
  • full mu opioid agonist
  • 5-10x more potent than morphine
  • analgesia: ++ to +++
  • dose-dependent sedation, respiratory depression, bradycardia
  • vomiting (45%)
  • panting (dogs)
  • hydromorphone-3-glucaronide can produce neuro-excitatory behaviours
  • adequate analgesia for invasive surgery
94
Q

What is important about methadone?

A
  • full mu agonist
  • NMDA antagonist
  • NE & serotonin uptake inhibitor
  • analgesia ++ to +++
  • clinically similar to morphine
  • no vomiting but panting
  • no active metabolites
95
Q

what is important about fentanyl?

A
  • 75-125% more potent than morphine, analgesia +++
  • intra & peri-operative pain
  • fast onset, short half-life (suitable for repeated boluses or INFUSIONS)
  • dose dependent respiratory depressant
  • dose dependent bradycardia (may require treatment w/ anticholinergics)
  • anesthetic sparing: isoflurane requirements are reduced by 53% (dogs)
  • highly lipophilic (v large volume of distribution & long elimination half life
  • too many repeated doses or too prolonged an infusion, may result in accumulation
  • prolong context-sensitive half-lives (long recovery time, more problem in humans that dogs & cats)
96
Q

What is important about Meperidine (Pethidine)?

A
  • synthetic mu & kappa agonist
  • 1/10th of the potency of morphine
  • short duration, mild anesthesia
  • histamine release
  • decreased incidence of GER compared to morphine
  • unique cardiovascular side effects vs other opioids
  • significant negative INOTROPIC effects when administered alone to conscious dogs
  • has modest ATROPINE-like effects (increase HR rather than typical bradycardia)
97
Q

what is important about remifentanil?

A
  • mu opioid agonist
  • similar potency to fentanyl
  • analgesia +++
  • ultra-short-acting: context-sensitive half-time: 4 min (post 4hr CRI humans)
  • only suitable for intraoperative use, need to administer other analgesics before infusion is terminated (to continue analgesia)
  • metabolized by blood & tissue non-specific cholinesterases
  • independent of hepatic function (useful for patients w/ hepatic disease)
98
Q

What is important about tramadol?

A
  • atypical mu receptor agonist
  • inhibits uptake of serotonin & norepinephrine
  • primary analgesic effect in humans is due to O-desmethyltramadol (M1 - 1st metabolite)
  • M1 acts as a full mu opioid agonist
  • analgesia (+)
  • Ca: do not produce substantial amounts of M1; analgesic effects are predicted to be weak at best
  • Fe: produce substantial amounts of M1 (likely an effective analgesic); bitter taste of oral preparation makes dosing a challenge
99
Q

what is important about buprenorphine?

A
  • partial mu agonist (weak kappa antagonist)
  • 1000x higher affinity for mu receptor than morphine
  • difficult to antagonize its effects
  • moderate intrinsic activity
  • analgesia ++
  • slower onset time than other opioids (15-30 mins)
  • long duration: 6-8 hrs
100
Q

What is important about butorphanol?

A
  • kappa agonist, mu antagonist
  • originally labelled as an ANTITUSSIVE agent in Ca
  • minimal effects on cardiopulmonary function
  • no histamine release
  • short-acting (30-90 mins)
  • analgesia (+)
101
Q
A

Anesthesia & Analgesia (30 decks)

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