pharm & tox ch 5 drug focus

full agonist

tightly binds to receptors & turn them on; produces maximal effect

opioid induced vomiting

happens because morphine stimulates receptors, which trigger the emetic center, & vomiting occurs

what receptors does morphine stimulate?

mu & kappa

good uses for morphine

treatment of visceral & somatic pain, for acute pain, as antidiarrheal & antitussive therapy for dogs

how is morphine absorbed?

when given by IV, IM, SC, & rectally — also orally but degree & rate of administered drug by circulatory system is reduced

side effects of morphine

vomiting, decreased GI peristalsis, body temperature changes (hyperthermia in cats, hypothermia in dogs), defecation after initial dose (dogs)

overdosage of morphine can cause…

CNS depression

if the patient has a sensitivity to the original dosage, what should be given?

partial dose

what can be used to treat respiratory depression?

naloxone

how is oxymorphone absorbed?

when given by IV, IM, SQ, & rectally

oxymorphone

more potent analgesic than morphine, but less antitussive activity

uses for oxymorphone

sedative agent, analgesic, & preanesthetic

what cardiac effects can oxymorphone have?

slows heart rate

methadone

class II drug; synthetic opioid agonist that eliminates withdrawal symptoms & relieves drug cravings by acting on opioid receptors in the brain

what does methadone block & in result causes?

receptor called NMDA, which helps to reduce some adverse opioid effects such as hypersensitivity

possible side effects of methadone

menial nausea/vomiting, sedation (dogs)

fentanyl

class II drug; short-acting mu agonist that is far more potent than morphine

what are the methods of administration for fentanyl?

IV constant rate infusion to dogs & patches

use transdermal patches with caution in patients who…

are older or have preexisiting respiratory conditions

how many hours must a fentanyl patch be on to reach therapeutic levels in dogs?

12 - 24

how many hours must a fentanyl patch be on to reach therapeutic levels in cats?

6 - 12

for how long does fentanyl provide analgesia?

48 - 72 hours in dogs, 4 days in cats

adverse effects of fentanyl

respiratory depression, bradycardia, urine retention, constipation

partial agonist

causes less receptor activation than full agonists

when given at lower doses, full agonists & partial agonists produce…

indistinguishable effects

as doses of partial agonists are increase, what will happen to the analgesic activity?

plateau — further doses will not provide additional relief but will extend duration of the drug’s effects

possible administrations of partial agonists

PO — can be absorbed by MM

buprenorphine

partial mu-opioid receptor agonist and kappa-opioid receptor antagonist; produces a dose-related analgesic effect, has a long duration of action

when is buprenorphine rapidly absorbed?

following IM injection

buprenorphine can cause…

decrease in heart rate & blood pressure, lower effects of respiratory depression, etc.

how much buprenorphine can be sent home with cats?

3 days worth

antagonists

bind to opioid receptors, effectively blocking them; do not activate receptors & they prevent receptors from being activated by agonist compounds

naloxone

antagonist that combines with my & kappa receptors to block/reverse effects of opioids — has no intrinsic activity

why is it more difficult for naloxone to reverse buprenorphine?

molecules bind very tightly to mu receptors making displacement more difficult

what can naloxone not reverse the effects of?

apomorphine

general anesthetics

produces unconsciousness & prevents the conscious perception of pain

propofol

injectable anesthetic, white in color; very rapid recovery time, usually given as an IV bolus (but not too quickly) — goes to the brain & follows the concentration gradient & moves from the brain to the blood

when does the animal wake up after being administered propofol?

as it leaves the brain

apnea

lack of/without breathing

barbiturates

ultra-short acting anesthetic

pentobarbital

shorter-acting barbiturate commonly used in euthanasia solutions

phenobarbital

long acting barbiturate commonly used as anti-convulsant in epileptic animals

ketamine & tiletamine are…

dissociate anesthetics

dissociative anesthetic

animals feel disassociated with its body — causes poor muscle reaction & cataleptic state with appearance of being awake but unable to respond to external stimuli

what kind of pain control does ketamine provide?

somatic (peripheral) ONLY

entomidate

choice of anesthetic used with patients who suffer from cardiac problems; given via IV only

adverse effects of entomidate

vomiting, hiccups, muscle contractions, etc.

alfaxalone

binds to GABA receptors; short duration of action, wide margin of safety; administered via IV

what happens if alfaxalone is mixed with a benzo (in same syringe)?

precipitates form

side effects of alfaxalone

dose-dependent depression from sedation to general anesthesia, excitement during recovery, tachycardia, hypotension (when inhaled), minimal cardiac depression

inhalation anesthetics

administration of drugs via the lungs & absorbed by alveoli into the blood & goes to the brain & produces unconsciousness

commonly used inhalant anesthetics

isoflurane, sevoflurane, desflurane

tranquilizers & sedatives

produces relaxed state, usually without significant analgesia

uses for tranquilizers

typically reduce anxiety

uses for sedatives

make animals sleepy but do not reduce anxiety or agitation

acepromazine

phenothiazine tranquilizer used to calm animals. No analgesia. Block dopamine receptors — can cause protrusion of nicitating membrane

benzodiazepine

causes calming & muscle relaxation effects in animals; no analgesia, good anti-convulsants — combined with anesthesia for good skeletal muscles relaxation

neuroleptanalgesics

opioid drugs mixed with tranquilizer/sedative, causes no loss of consciousness — may decrease some of the adverse effects of the opioid

doxapram

CNS stimulant that increases respiration in animals with apnea or bradypnea

alpha-2 agonist

med that stimulates alpha-2 adrenergic receptors in the central nervous system to decrease sympathetic nervous system activity, lower blood pressure, and reduce heart rate

what is the toxic compound found in chocolate?

theobromine