Preanesthetic medication Flashcards
Reasons for premed
To calm or sedate an excited, frightened or viscous animal
To minimize adverse effects of concurrently administered drugs
To reduce the required dose of concurrently administered agents
To produce smoother anesthetic inductions and recoveries
To decrease pain and discomfort before, during, and after surgery
To produce muscle relaxation
Pre-emptive analgesia is and why to utilize it
To provide analgesia before tissue injury, including surgery (and after)
Reasons to utilize pre-emptive analgesia
More effective analgesia and takes less medication than treating pain that already exists
Limiting pain before it occurs allows lowering overall amount of anesthetic required and therefore decreases drug risks
Speeds up recovery times
Considerations for selection of preanesthetic protocol
Species and breed
Temperament
Patient history
Physical status of patient
Availability and compatibility of drugs
Route available in that patient (PO,IV,IM,SQ)
Comfort with specific drugs
Procedure
Facilities available
Administering Premedication:
In general, time to effect of preanesthetic:
30-40 min before induction of SQ
10-20 min before induction if IM
3-10 minutes if given IV
Effects will be more pronounced and faster
More pronounced side-effects
Often requires an IV catheter
Patient to be left in quiet for drugs to have full effect
Excited patients require a higher dose of drug for equivalent sedation
Assessing sedation
Parasympathetic signs
prolapsed 3rd eyelid, drooling, constricted pupils
Ataxia
do not leave unattended; anxiety
Recumbency
Decrease in HR, RR, (BP)
Certain drugs can relax inhibitions and animals can become aggressive or exhibit other unusual behaviours
Preanesthetic precautions
Overdose can result in sufficient CNS depression to cause death
In very sick animals, recommended doses can cause lethal overdose
Horses that develop ataxia as a result of sedation can become anxious and enter “fight or flight”
Brachycephalic breeds should be continuously monitored under sedation
Relaxation of the elongated soft palate can cause the airway to close
3 main groups of premedications and would you mix them
Anticholinergics
Tranquilizers and sedatives
Phenothiazines
Benzodiazepines
Alpha 2-adrenoceptor agonists (alpha2-agonists)
Opioids
Usually used in combination of 2 or more of the above drugs
DO NOT MIX TWO OR MORE DRUGS UNLESS YOU HAVE A RELIABLE EVIDENCE IT IS SAFE TO DO SO!!
Anticholinergics work on what system and are they controlled
PSN and non controlled drug
Indications of anticholinergics
To counter the parasympathetic effects of many of the other drugs used in balanced anesthesia
Prevent and treat bradycardia
Decrease salivary secretions arising from parasympathetic stimulation (aids in intubation)
Mydriasis (prevents rolling of the eyeball and opens pupil for eye surgeries)
Routes of admin for anticholinergics
Im, SQ, IV and IT (intertracial)
Major effects and adverse effects of anticholinergics
Prevention of bradycardia
Increased HR
Cardiac arrhythmias
Reduction and thickening of resp secretions
Bronchodilation
Mydriasis
Reduction of GI, salivary,, and lacrimal secretions
Inhibition of peristalsis - colic horses
Tranquillisers and sedatives work by and act on what system
Centrally-acting
Cause depression of the CNS
Are tranquilizers and sedatives part of a balanced anesthesia plan and why
Part of balanced anesthesia
Smoother induction
Allows decreased dose of general anaesthetic
Patients recovery faster
Are tranquilizers and sedatives controlled drugs
Many are controlled drugs
Controlled drugs and narcotic act
Record! For inventory and with each individual use
Practice standards: lock and key, strict record of use
Indications of tranquilizers and sedatives
Tranquilizers = reduces anxiety but does not necessarily decrease awareness and wakefulness
Sedative = causes reduced mental activity
The effects of these drugs often overlap because they produce both effects to some degree, to the terms tranquilizer and sedative are often used interchangeably
Different types of tranquilizers and sedatives
Phenothiazines
-Acepromazine
Benzodiazepines
-diazepam (Valium@)
-midazolam (Versed@)
Alpha2-adrenoceptor (alpha2-agonists)
-xylazine (Rompun@)
-dexmedetomidine (DexDomitor@)
Phenothiazines (tranquilizer and sedative) effects what system and is it controlled
Ex. acepromazine
Non-controlled (not technically Pr either)
Approved for horses, dogs and cats
Injectable and oral formulations
No reversal
major side effects and adverse effects of phenothiazines
Reduction of the seizure threshold
Tachycardia or bradycardia
Antiarrhythmic vasodilation
Hypotension
Antiemetic effects
Mechanism of action for phenothiazines
Blocks receptors in the basal ganglia→ CNS depression
Blocks alpha1 adrenergic receptors
Some antihistamine effects
Physiological effects of phenothiazines
Causes calming, reluctance to move and decreased interest in surroundings
Decreased spontaneous activity, ataxia
Vasodilation (due to blocking of alpha1-receptors
Suppressors chemoreceptor trigger zone (antiemetic)
Will slowly cross the placenta
Clinical use of phenothiazine
Anti-anxiety and sedation (relatively mild)
Chemical restraint ot ease handling
Travel
Decreased dose of general anesthetic
Eases induction and recovery
Blocks morphine-induced excitement in cat
Antispasmodic
Antiemetic (decreases vomiting when used together with hydromorphone as preanesthetic)
Common side effects of phenothiazines
Vasodilation (alpha1 receptor blockade); causes hypotension→ monitor BP
Hypothermia in small animals
Sequestering of RBCs in the spleen
Causes splenic enlargement and drops PVC
Caution in splenectomies, anemia
Overdose may cause rigidity or tremors
Ptosis, prolapsed 3rd eyelid in dogs and cats
Can cause aggression of excitement
Other considerations of phenothiazines
Bradycardia but less than many other agents
No analgesia
Antiemetic
Prevents histamine release and decreases allergic response
Worsens depressive effect of other drugs in the resp system
Metabolized by liver
Side effects specific to horses of phenothiazines
Penile prolapse
Facilitates sheath cleaning, examination
But can be irreversible
Caution in breeding stallions
Possible excitement, sweating, tachypnea
Relative contraindications of phenothiazine
Breeding stallions- penile prolapse
BOXERS- may exacerbate underlying arrhythmias
Also avoid in severely debilitated, neonates, geriatrics, preexisting hypotension (blood loss, shock, dehydration), CHF, liver disease, CRF
Related to vasodilation and resultant hypotension
Always use caution when sedating brachycephalic breeds
How to use acepromazine
Can also use alone for anti-anxiety and minor restraint
Used in combination with other drugs for pre-anesthesia
There is a mg/kg dose AND a maximum dose
Increasing the dose does NOT increase sedation but does increase hypotension due to peripheral vasodilation
Works better if not already excited; excitement can decrease the effect
Lasts 4-8 hours
Do not combine with dexmedetomidine
No reversal. If overdose, provide supportive care
Support BP-fluids
Increase the sympathetic response
Butyrophenones is what
Azaperone/Stresnil@
Drug class: butyrophenones (similar to phenothiazines)
Only used in pigs
Very unpredictable results in other species
Blocks dopamine and norepinephrine activity in the CNS
Clinical indications for azaperone
Decreases aggression/fighting during weaning and mixing
Premedication and sedation (castrations)
Antiemetic
Decreases malignant hyperthermia
Potentially fatal genetic condition; increased metabolic rate and muscle activity in response to isoflurane, transport/handling stress
Most commonly occurs in pigs
Benzodiazepines is/when to use/ is it controlled
Ex. diazepam (Valium@), midazolam (Versed@)
Controlled (schedule IV of the controlled drugs and substances act)
Most not labelled for veterinary use therefore an example of ELDU
Injectable and oral (tablets) formulas available
Major effects and adverse effects of benziodiazepines
Antianxiety and calming
Anticonvulsant activity
Disorientation and excitement in young, healthy dogs
Dysphoria and aggression in cats
Muscle fasciculation in horses
Ataxia in recumbency in large animals
Few cardiopulmonary effects
Skeletal muscle relaxation
No analgesia
Does benzodiazepines have a reversal agent
Reversal → flumazenil
Mechanism of action for benzodiazepines
Increase GABA levels in the brain
GABA is an inhibitory neurotransmitter
Indications of benzodiazepines
As part of balanced anaesthesia
Premed to smooth induction and recovery
Can combine with ketamine for induction
Other common indications
Antianxiety to sedation; behavioural modifier
Anticonvulsant for treating seizures
Skeletal muscle relaxant (including urethral relaxation)
benefits of benzodiazepines
Minimal CV effects at appropriate dose
Dose cause dose-dependent resp depression
Smoother induction and recovery
Decreases amount of inhalant GA required
Increase skeletal muscle relaxation
Is benzodiazepine reversable
Reversible drug class
In the event of overdose or adverse reaction, can give the reversal agent (aka antagonists or antidotes)
Precautions of benzodiazepines
Sedation is not always reliable when used alone in animals
Dysphoria/excitement can occur
May unmask latent aggression in some animals (animals lose inhibitions)
Precautions with horses on benzodiazepines
Muscle fasciculation
Weakness, ataxia
Do not give alone except for seizures in adults
Contraindications of benzodiazepines
AVOID in pregnancy/caesarean
Will cross the placenta
Causes similar to FLOPPY BABY SYNDROME
Skeletal muscle relaxation in the neonate
Asphyxiation form relaxation of resp muscle
Diazepam is what drug class and used on what
Benzodiazepine
Commonly used
Dog, cat, horse, pig
Clinical indications of diazepam
Anticonvulsant for emergency treatment of seizures
Antianxiety (noise phobias) at lower dose
Sedation in some patients at higher dose
Must be used in combination with other drugs in cats and horses (and some dogs) or may cause excitement
Skeletal muscle relaxant
Relaxes urethral sphincter (blocked cats and dogs)
Can mix with ketamine for induction (KetVal)
Indications of diazepam
Inexpensive
Can be administered by many routes:
IV solution- painful/unreliably absorbed if given IM/SQ
Can give intrarectal if seizing patient
Also available as oral tablets
Dose varies depending on the route
Lasts 30 min - 2h
May cause a prolonged hangover effect
Historically used as appetite stimulant in cats- doesn’t really work-risky
handling and storage of diazepam
Controlled drug
Not water soluble
Will form precipitate if mixed with other drugs
Never use if precipitate forms
Only exception is KETAMINE (KetVal)
Store IV solution in glass containers
Drug binds to plastic with time
Keep from light
Flush IV lines immediately after administering
Binds to plastic and will form precipitate if still present in line/verin when drug is administered
Adverse effects; contraindications of diazepam
Contradiction for caesarean
Floppy baby syndrome
Depressed, poor muscle tone, excessive sedation
Aggressive dogs
Can bring latent aggression
Using alone in horses
Excitement and ataxia
Cats
Can cause sudden liver failure- increase risk with increase doses
Therefore avoid use as an appetite stimulant
midazolam/Versed@ is what type of drug class and used when
Benzodiazepines
Very similar to diazepam
Easier to use, but more expensive
How is midazolam different from diazepam
Twice as potente
Shorter acting
Compatible with many agents as it is water soluble
Can give IM, SQ, IV
CANNOT use alone
Not used as anticonvulsant
Flumazenil is what drug class
Antagonsit
Flumazil works for what drugs
Reversal agent (aka antagonist) for benzodiazepines including diazepam and midazolam
How does flumazil work
Binds to and blocks GABA receptors
More attraction for the GABA receptor then the benzodiazepines
Therefore, knocks of any benzodiazepine drug already bound to the receptor
Little to no effect on its own
Solemn used because $$$$ and short duration of action of diazepam/midazolam
Is Alpha2 adrenergic agonists (tranquilizer and sedative) controlled
No
Alpha2 adrenergic agonists effects and adverse effects
Dose dependent sedation that can be profound
Analgesia
Agitation or aggression when touched
Reaction to loud noises
Muscle tremors in horses
Cattle often lie down
Initial hypertension, bradycardia, and pale MM followed by hypotension, decreased cardiac output, and a little further decrease in the heart rate
Severe decrease in heart rate, BP, cardiac output, and tissue perfusion especially when high doses are given
Respiratory depression that can be severe
Muscle relaxation
Vomiting in cats and dogs
Adverse GI effects (bloat and colic)
Hyperglycemia
Hypothermia
Increased urination
Premature parturition in cattle
Horses may sweat
Large animal apla2 adrenergic agonist
Xylazine (Rompun@)
Detomidine (Dormosedan@)
Romifidine (Sedivet@)
Small animal alpha2 adrenergic agonist
Dexmedetomidine (Dexodomitor@)
Is the drug class Alpd2 adrenergic agonist reversable
Yes
Mechanism of action of alpha2 adrenergic agonist
Drugs bind to alpha-2 adrenergic receptors
Activation of alpha 2 receptors causes inhibition of release of norepinephrine and dopamine
Decreases overall sympathetic response
Metabolized by the liver; excreted by the kidneys
Physiological effect of alpa2-recptor activation
Overall CNS depression
Decreased overall ability to respond to stimuli
This action is enhanced if given together with an opioid or other sedative or tranquilizer
Decreases sympathetic response
Bradycardia- consistent, immediate, significant; as low as 12 bpm in a large dog
Resp depression
Increases parasympathetic nervous system
Increased GI motility (except in ruminants)
Indications of alpha2 adrenergic agonist
Rapid and reversible sedation
Mild analgesia on own
Can be used for neuroleptanalgesia
Occurs when alpha-2 agonist is combined with an opioid and given at a fairly high dose
A state of lack of awareness associated with very heavy sedation combined with strong analgesia
Used for minor procedures e.g. suturing lacerations in horses
Centrally-mediated muscle relaxation
adverse effects of alpha 2 adrenergic agonist
Severe hypotension
Can hyperventilate on room air
Possible arrhythmias with some of the older drugs
Increased risk if given too fast IV
Increased risk if also given atropine
Ataxia
Cattle can become recumbent, decreased rumen motility, risk of bloat and may cause abortion
Horses can become reactive to stimuli if give alone- noise, touch
Emesis in cats
Why does alpha 2 adrenergic agonsit cause hypotension
Related to significant bradycardia
Decreased pulse, MM become very pale
Do not use with acepromazine in small animals
Why can animals hyperventilate on room air when under alpha 2 adrenergic agonist
Decreased RR and resp volume
Enhances the resp depressant effect of other sedatives and anesthetics
RESPIRATORY DISTRESS IN BRACHYCEPHALIC DOGS
Ruminant very sensitive to resp effects
Warning and contraindications of alpha2 adrenergic agonist
Avoid or use extreme caution in pediatrics, geriatric
Avoid if severely dehydrated, in shock, cardiovascular disease, severe resp disease, or severe renal disease
Avoid if advanced liver disease
Avoid or use extreme care with acepromazine
Acpreomazine→ severe hypotension from combination of bradycardia and vasodilation; will plummet the BP and there is no way to bring it back other then reversal
However it can be fail safe group IF you have reversal on hand
MONITOR! MONITOR! MONITOR!
Using alpha2 adrenergic agonists
IM (15-20 min onset), IV (1-3 min onset)
Duration of sedation is 30-60 min
Don’t give IV too fast or will enhance the resp and cardiac depression effects
When using IV, should “give to effect” only until desired degree of sedation is achieved
Avoid SQ
Very lipophilic; drug will bind to fat and absorption will be unpredictable (can severely delay effect)
Decreased effect if stressed or fearful
Indications of xylazine
Equine and bovine
Premed
“Standing sedation”
-For castrations, wound repairs, caesareans
Sedates animal without becoming recumbent
Colic
-Excellent visceral analgesia
30 min of analgesia if given as an epidural
Part of “Triple Drip”
-Injectable GA, to be discussed with ketamine
Two concentrations 20mg/ml or 100mg/ml
-Lower concentration in cattle b/c of increased rep and GI effects
IV “to effect”
-IV has more pronounced heart and resp effects
IM
-Onset of action occurs 10-15 minutes after Im injection
-Duration of action is approx. 30 min
Epidural
-Visceral analgesia
Often combined with an opioid (ex. butorphanol) or valium for better sedation and longer duration
Adverse effects of xylazine
Cattle require 1/10 of dose compared to horse
-Even at recommended dose can have severe resp effects, cause GI stasis (i.e., bloat) risk of aspiration pneumonia
Horses
-Sweating
-Ataxia, wide-based stance
-Horses can become excited if used alone
-Never given intra-arterial in horse; will cause excitement/seizure/collapse
-Avoid in neonatal foals as the lowered HR cannot maintain blood flow
detomidine/Dosmesdan@ are used in what and what drug class
Alpha2 adrenergic agonist
labeled for horses
detmoidine works by/for
Similar to xylazine
Visceral analgesia
Give slowly IV to effect
Can give alone or with opioid
Severe hypotension and bradycardia
Twice the duration and stronger sedation
Used for standing sedation
Never use with IV sulphonamides→ heart failure
romifidine/Sedivet@ is used for and why
Labelled for horses
Similar to xylazine, detomidine
Fast acting, long lasting
Severe hypotension and bradycardia
Sedative or pre med
Can use at low dose
Anxiolytic with minimal ataxia
dexmedetomidine/Dexdomitor@ is used for and when
Small animal
Sedation (60-90 min); analgesia (30 min)
Sedation
Hip rads, minor procedures (with local anesthetic), quills
Premed
Sedation and pre-emptive analgesia
On going sedation if given as CRI
Indications of dexmedetomidine
Usually given in combination with opioid
Better analgesia
Better sedation
Dresses the mg/kg dose of dexmedetomidine required→ decreases adverse side effects
Most commonly with butorphanol or buprenorphine
Will see more resp depression is combined with hydromorphone
Dosing of dexedetomidine
The label dose is 10x to 20x what is used in clinic
Label dose is intended for heavy sedation with dexmedetomidine alone
When combined with opioids and/or with balanced anesthesia, only use at 1/10 to 1/20 the labelled dose
Is also labelled for indication at higher doses (not usually done)
As animal size increases, the mg/kg dose decreases
How to administer dexmedetomidine and how long does it work for
IM takes 15-20 min onset time
NEVER give SQ- drug deposits in fat and releases unpredictably
Give IV to effect
Dog only
Do NOT give to rapidly, can stop breathing
1-3 min onset
Can give ½ IM, wait 15 min, give remainder IV to effect
Adverse effects of dexmedetomidine
Profound bradycardia and resp depression (much more noticeable in dogs)
Monitor HR and BP
HR will drop significantly; 16 (large K9), 40 (small K9)
Monitor BP and pulse strength
Monitor MM
Will be pale; should never be cyanotic
Monitor oxygenation
Extend neck
Place on flow-by 100% O2 if available
Place IV catheter
If in doubt, place ion IV fluid support
Caution and contraindications of dexmedetomidine
Do NOT use with atropine
-Heart block, heart failure
Extreme caution of avoid with acepromazine
-Profound hypotension
Extreme caution when followed by isoflurane in cats
-Iso causes more extreme vasodilation then acepromazine
Avoid if hypotensive dehydrated, geriatric, debilitated
Alpha2 antagonists is what type of drug
Reversal
Reversals have a greater affinity for receptor then the agonist drug
Alpha-2 antagonist for LA
Yohimbine (Yobine®)
Tolazoline (Tolazine®)
Alpha-2 antagonist for SA
Atipamezole (Antisedan®)
Designed so you give equal VOLUME as Dexdomitor® for complete reversal
Alpha 2 antagonist works by
Effects specific to alpha2 agonist- does not affect other drugs
Reversal of the sedative, cardiovascular AND analgesic effects of the corresponding agent
Few adverse effects at clinical doses, but significant adverse effects if too much is given by increasing sympathetic tone
GI, neurologic, and cardiovascular effects
Excitement, muscle tremors, hypotension, tachycardia, salivation, vomiting, diarrhea
Opioids work as
Analgesia
-Strongest analgesics available in vet med
Preanesthetic
-Pre-emptive analgesia – giving before pain occurs results in less post op analgesia required and shorter recovery times
-Sedation
-Decrease total dose of GA required
Anesthetic induction
-At higher doses, some opioids can produce unconsciousness (uncommon)
What are opioids used for
Majority have wide margin of safety at therapeutic dose (Higher Potency → Lower Therapeutic Index)
Where are opioids metabolized
Metabolized by liver with renal excretion, therefore
Caution in very young, very old, debilitated
Caution in very ill (including head trauma, shock, HBC)
Caution if respiratory system is compromised
Are opioids controlled
Yes
Neuroleptanalgesia is and how to induce it
A profound state of sedation and analgesia
Induced by simultaneous administration of an opioid and a sedative
Ex. Dexmedetomidine + hydromorphone; xylazine + fentanyl
Commonly given for minor procedures or indication
Causes CNS depression to state of borderline unconsciousness
Can be aroused by extreme stimulation, noise
Routes of administration of opioids
IM
SQ
IV
PO
Rectal
Transdermal
Subarachnoid
Intraarticular (joints)
Epidural
Neurolepetangelasia , when given IV, must be done so slowly to avoid CNS stimulation
Mode of action of opioids
Drugs work by binding to opioid receptors
Although opioid receptors found on neurons throughout the body, analgesic and sedative effects are primarily the result of their action on receptors located in the brain and spinal cord
Brain- sedation and analgesia
Spinal cord-analgesia
Smooth muscle of the rep tract, GI tract, urinary tract
Major types of opioid receptors
Mu (μ)
Kappa (κ)
Delta (δ)
Mu opioid receptor works for
Supraspinal analgesia
Moderate to severe pain
Sedation
Resp depression
Bradycardia
Miosis (mydriasis in cats)
Hypothermia (hyperthermia in cats)
Euphoria /dysphoria
GI stasis (constipation)
Urinary retention
CRTZ (chemoreceptor trigger zone) for vomiting
Antiemetic at the vomiting center
Kappa opioid receptor works for
Spinal analgesia
Mild to moderate pain
Miosis
Mild sedation
Little resp depression
Diuresis
Classes of opioids
Pure agnostic
Partial mu-agonist
Agonist-antagonist
Pure antagonists
What determines the class the opioid is in
Opioids are placed into “classes” based on which receptor they bind and whether binding causes the receptor to be turned on (agonist), partially turned on (partial agonist) or turned off (antagonist)
Pure agonists work by
Drugs bind to and turn on the mu-receptor
May also turn on kappa-receptor
Provides the best analgesia (treats moderate to severe pain)
Mu-antagonist provides the best analgesia. Drugs with a higher affinity for the mu-receptor provide more analgesia
Also produces sedation
Highest risk of addiction
Morphine, hydromorphone, oxymorphone, fentanyl, meperidine, hydrocodone, tramadol
Pure agonists side effects
Side effects as listed for the mu receptor (resp depression, GI stasis, hypothermia, occasional hyperthermia in cats); analgesia and sedation are better if also has kappa activity
Partial mu-agonsits work by
Binds to and partially activates the mu-receptor
Partial mu-agonists physiological effect compared to pure agonists
Less analgesia
Less resp depression
Less GI stasis
Less euphoria
Less hypothermia
When to use partial mu-agnosists
Indicated for slight to moderate pain
Also used to “partially” block the effects of a pure mu-agonist that is given at the same time; i.e., acts as a partial reversal
Buprenorphine (partial mu-agonist; kappa antagonist)
Agonist-antogonist opioids work by
Simultaneously turns on kappa-receptor (kappa-agonist) while blocking mu-receptor (mu-antagonist)
Physiological effects of agonist-antagonist opioids
Mild analgesia
Sedation
Less resp depression and less GI effects than the pure or partial agonists
May cause dysphoria
When to use agonist-antagonist opioids
Can be used to “completely block” either mu-agonist or partial mu-agonist activity
Butorphanol (kappa-agonist; mu-antagonist)
Pure antagonists work by
Binds to both mu-receptors and kappa-receptors but does not produce any activity
Effectively acts as a block
“Reversals”
Naloxone
Naltrexone
Direnorphine (M-50) is the reversal agent specifically created for etorphine (M-99)
Major side effects of opioids
Resp depression
Most common cause of death in case of OD
Centrally-mediated; decreases RR and tidal volume
Also inhibits the CO2-drive that stimulates breathing
Ventilation should be monitored and O2 available
Bradycardia
Hypothermia in all species
Occasional hyperthermia in certain cats is due to a mu-receptor response especially hydromorphone and can be fatal if not treated
Caution using in patients with brain trauma or cerebral edema; can increase brain swelling
Sedation
Non-life-threatening side effects of opioids
Vomiting
GI stasis (constipation)
Dysphoria, excitement, hallucinations, startle response in cats
Addiction
Why does opioids induce vomiting
Activates the chemoreceptor trigger zone in the brain
Often with first dose of mu-agonists in healthy pain free animals
Can block/decrease with acepromazine or diazepam
Why does opioids cause GI stasis
More likely with chronic use
Avoid or caution in colic, bloat, FB surgeries (enterotomies)
Why does opioids cause addiction
Mu-receptor mediated
Receptor down-regulation means may need to increase dose or dosing frequency to manage chronic pain
Variable side effects of opioids
Variable effects may or may not occur depending on the specific opioid, dosage, route of administration and species
Antitussive (codeine, hydrocodone, butorphanol; to treat cough)
Vomit (apomorphine; IM hydromorphone)
Diarrhea and flatulence
Miosis in dogs; mydriasis in cats and horses
Excitement, dysphoria, whine/bark (dogs), increased motor activity (horse), increased sensitivity to noise
Hypotension/hypertension
Changes in urination
Excess salivation
Panting in dogs
Hyperthermia in cats
Sweating in horses
Pure mu agonists examples
Morphine
Fentanyl
Hydromorphone
Methadone
Meperidine
Sufentanil
Cerfentanil
Indications of morphine
Mu and kappa agonist
Indications
“Opioid standard of reference)
All other opioids are compared to morphine
Mild to moderate sedation dose dependant
Analgesia for moderate to severe pain
Routes and duration of morphine
IV, IM, SQ, PO, intra articular, epidural
Duration of action
3-4 hours
Side effects of morphine
Excitement or dysphoria in cats, horses
Mydriasis in cats, horses
Drowsiness in dogs
Severe resp depression with high doses
Nausea/vomiting
GI stasis (oral form is worse)
Histamine release can cause systemic vasodilation
Fentanyl indications and potency
Mu and kappa agonist
50-100x the potency of morphine
Indications
Neuroleptanalgesia
Induction
Analgesia (provided frequent administration)
Routes and duration of action of fentanyl
IV bolus
CRI (preferred IV method)
Slow release transdermal patch
Epidural
Duration of action
1-2 min onset; 10 min duration of action IV
Usually CRI or slow release transdermal patch for analgesia
Side effects of fentanyl
Defecation or constipation
Resp depression
Bradycardia
Hypothermia
Panting, drooling
Dysphoria, agitation
Sedation
Not approved for food animals
Hydromorphone indications
Mu and kappa agonist
Indications
5-10x the potency of morphine
Moderate to severe pain (visceral and somatic)
Pre, peri and postoperative pain control
More sedation than morphine
Rarely used in large animals because of lack of info about efficacy or adverse side effects
Duration of action by route for hydromophone
IV 1-2 hours
IM 2-4 hours in dogs, longer in cats
SQ up to 6-8h
Epidural 8 hrs
Side effects of hydromorphone
Reliable emetic with first dose, especially if SQ/IM
Diarrhea with first dose; constipation with chronic use
Pant, drool
Mydriasis in cats and horse
Excitement /hallucinations in cats and horses
Adverse effects of hydromorphone
Resp depression
Use with caution or contraindicated if severe resp disease
Most common cause of fatality
Bradycardia
Hypothermia in all species
Can cause occasional hyperthermia in cats which can be fatal
In the event of a severe adverse reaction, can partially reverse with buprenorphine or butorphanol; can completely reverse with naloxone, naltrexone
methadone indications
Mu and kappa agonist
Indications
5-10x the potency of morphine
Moderate to severe pain (visceral and somatic)
Low incidence of vomiting (compared to morphine or hydromorphone); other side effects similar to other pure mu agonists
Excellent article summarising methadone released in the CVJ last year
Duration of action for methadone
Duration of action ~4hrs
This is slightly longer than morphine and hydromorphone
What can you use methadone on
Methadone is relatively new in canada
Currently only licensed for use in cats; however, it is licensed for use in cats and dogs on other areas (Australia, New Zealand countries within the UN and EU) as an analgesic and preanesthetic agent
Licensed in Canada: 0.5mg/kg IM in cats prior to spay or neuter.
Extra-label: commonly used 0.2-0.5mg/kg administered IV, IM or SC
meperidine/Demerol@ indications
Mu and kappa agonist
Indications
1/10x morphine
Mild to moderate pain
meperidine/Demerol@ route of action and duration
Routes
IM injection, NOT IV or SQ
Histamine release with IV use
Duration of action
30-90 min
Side effects of meperidine
No vomiting or bradycardia
Use as premedication when no vomiting required
Sufentanil works on what receptor
Super mu-agonist”
500-1000X the power of morphine
But shorter acting than fentanyl
Indications of sufentanil
Intraoperative analgesia in dogs and cast as an infusion
Induction
Carfentanil works on what receptor
“Super mu-agonist”
10,000-100,000X the power of morphine
Indications of carfentanil
Wildlife capture and immobilization
Why is carfentanil super dangerous for people
Potentially fatal if handler scratches/injects self
Use with extreme caution
Wear double gloves when handling closed bottle
Reversal of carfentanil
Requires naltrexone for reversal
Draw up BEFORE handling carfentanil
Partial mu agonists is
Buprenorphine
-Partial mu agonist, kappa antagonist
Indications of buphenorphine
1/20x morphine
Mild to moderate pain
Less sedation
Onset of action ~30 min
Routes and duration of action for bupernorphine
IV, IM, SQ, epidural or trans mucosal (in cats)
Place in the buccal cavity or sublingual and allow absorption through the oral mucosa
Will NOT work if swallowed
Duration of action
6-8 hours in dogs and cats
2 hrs in sheep
Side effects of buprenorphine
Fewer side effects than hydromorphone due to partial mu-activity
Slightly dysphoria
Reversal of buprenorphine
Higher affinity than naloxone, therefore requires much high doses or infusion of naloxone to reverse buprenorphine
What drug is a Agonist- antagonist (kappa agonists, mu antagonist)
Butrophanol/Turbugesic@
indications of butrophanol
½ to 1x morphine
Mild to moderate pain
Analgesia and sedation are via the kappa-receptor
Ex, colic
Sedation
Antitussive
Reversal of hydromorphone
SA (0.5mg/ml) and LA (10mg/ml) concentrations
Routes used for butrophanol
IV, IM, SQ, PO
Side effects of butrophanol
No mu-receptor mediated side effects
Less resp depression
No excitement
No GI stasis
No panting in dogs
How does butrophanol work as a reversal
Binds to and blocks mu-receptor
Activation of kappa receptor produces mild to moderate analgesia and some sedation
If butorphanol and hydromorphone are both present, butorphanol will bind to the receptor because it has 30X the affinity for the receptor compared to hydromorphone. Result is to kick out the hydromorphone and/or prevent the hydromorphone from binding to the receptor
Opioid antagonists (reversal) indication
Reversal of desirable and undesirable effects of opioid agonists, partial agonist, or agonist-antagonist including sedation and analgesia
CNS and resp depression
Routes of admin for opioid antagonists
IM, slow IV
major effects and adverse effects of opioid antagonsits
Reversal of desirable and undesirable effects
Sedation, dysphoria, panting, resp depression, hypotension, bradycardia, GI effects and analgesia
The action of opioid antagonists if often dramatic, causing patient to appear nearly unaffected shortly after administration
Naxalone is what type or reversal
Pure antagonist
Naloxone indications
Complete reversal of both mu and kappa agonists
Will lose all adverse effects and all analgesia
Dog, cat, horses, exotics, people
1 drop under tongue of neonates after C-section to reverse resp depression of opioid given to the mother
Duration of action and time of onset of naloxone
Duration of action
30-40 min; will need to top up
Time of onset
2 min IV
Aggressive use can cause catecholamine related cardiac arrhythmias and vasoconstriction leading to pulmonary edema
Naltrexone indications and duration of action
(pure antagonist)
Both mu and kappa antagonist
More potent than naloxone
Used to reverse carfentanil in wild life
Can be used intranasally
Duration of action
Long lasting (hours)
Butorphanol/Torbugesic@ (Partial antagonist)
Kappa agonists, mu antagonist
Only blocks mu activity; adds to kappa activity
Not very strong reversal
Leaves sedation and some analgesia
Will reverse resp depression and hypo/hyperthermia
What drugs are pure antagonist
Naloxone
* Naltrexone
* Diprenorphine (M-50) is the reversal agent specifically created for etorphine (M-99)
What drugs are pure mu agonists
Morphine
Fentanyl
Hydromorphone
Methadone
Meperidine/demerol
Sufentanil
Cerfentanil
What drugs are partial mu agonsits
Buprenorphine
What drugs are kappa agonists and mu antagonist
Butorphanol/Turbugesic
Side effects of Mu receptor opioid
Resp depression
Bradycardia
Miosis (mydriasis in cats)
Hypothermia (hyperthermia in cats)
Euphoria /dysphoria
GI stasis (constipation)
Urinary retention
CRTZ (chemoreceptor trigger zone) for vomiting
Antiemetic at the vomiting center
Side effects of kappa receptor opioids
Miosis
Mild sedation
Little resp depression
Diuresis
