Term
| which analgesic drugs are most widely used peri-operatively? |
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Definition
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Term
| How can opiods be classified? |
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Definition
1-agonist, partial agonist or antagonist action 2-which opiod receptor they bind to - μ, κ or δ
(generally μ analgesia> κ analgesia - poss gr. κ analgesia in birds)
3-duration of action |
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Term
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Definition
| have affinity for the opiod R an once bound they exert a specific effect |
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Term
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Definition
-bind to the same R as agonists
-at low doses have a similar dose-dependent activity profile as agonists
-at higher doses R activation does not incr. proportionally w. dose
i.e. the dose-resp. curve for a partial agonists flattens mush quicker than full agonists
-partial agonists reach maximal activation at much lower doses than full agonists |
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Term
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Definition
| have affinity for the opiod receptor but once bound they block the R and do not cause a response |
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Term
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Definition
there is no "maximum dose" if in pain - but side effects will occur if not in pain!
-dose opiods according to analgesia required - switch to a different opiod / use multimodal analgesia if ineffective |
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Term
| Analgesic effects of opiods |
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Definition
μ agonists most effective analgesics
NG: generally more potent = gr. likelihood of clinically significant s. effects |
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Term
| Sedation effects of opiods |
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Definition
-usually dose- and drug- dependent
-sedation from phenothiazines and alpha-2-agonists is enhanced when combined w. opiods |
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Term
| Resp system effects of opiods |
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Definition
-fentanyl given IV intra-anaes. if likely to cause clinically significant resp. depression and animals may rquire vent. support
-morphine, methadone and buprenoprhine do not cause clin. sig. resp. depression at normal dose rates |
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Term
| CV system effects of opiods |
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Definition
-few negative effects on blood movement
-can cause decr. HR through stimulation of vagal nerve (can manage w. co-admin of an anticholinergic) - most apparent when given IV or in high doses |
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Term
| GI system effects of opiods |
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Definition
-morphine directly stimulates the V centre - animals often vomit shortly after premed / sedation admin
-less apparent / not evident if post-op for pain mgmt |
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Term
| Routes of admin of opiods |
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Definition
-IV if given repeatedly
-IM can be painful - care
-SC not common (not as good absorption)
-transdermal - care as variable absorption between animals, so some animals receive sub-analgesic levels - always use a part of multi-modal analgesia
-transmucosal (buprenorphine in cats) - almost 100% bioavailabilty - faster than IM and comparable w. IV admin - avoids the need for repeated injections and can be used bu owner at home
-also epidural, intraarticular
-NOT oral - big first pass effect |
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Term
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Definition
care as variable absorption between animals, so some animals receive sub-analgesic levels
- always use a part of multi-modal analgesia |
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Term
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Definition
(buprenorphine in cats)
- almost 100% bioavailabilty
- faster than IM and comparable w. IV admin
- avoids the need for repeated injections and can be administerd by owner at home |
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Term
| Use of intra-op opiod analgesia |
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Definition
-painful procedures
-if CV unstable / sick patients as part of balanced anaes. technique
-CRI preferable to bolus (w. bolus care not to induce apnoea) |
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Term
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Definition
-μ-agonist
-2-4hours duration
-Admin: IM, IV, SC - dilute and give slowly. Single or CRI
-clinical use: premed / top-up analgesia during surgery / post op analgesia
side effects: may induce V pre-op when animal not in pain, can induce histamine release when given IV |
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Term
| Methadone (vet. license dogs, cats soon) |
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Definition
-equi-efficacious c.f. morphine
-μ-agonist
-2-4hours duration
-Admin: IM, IV, SC. Usually single rather than CRI to avoid accumulation
-clinical use: premed / top-up analgesia during surgery / post op analgesia
Side effects: does NOT induce V |
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Term
| Pethidine (vet. license dogs and cats) |
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Definition
-less efficacious c.f. morphine
-μ-agonist
-1-1.5 hours duration
-Admin: IM, SC. Need freq. dosing due to v. short acting. (not IV due to histamine relase)
-clinical use: premed / post op analgesia
Side effects: anticholinergic or antispasmolytic effects |
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Term
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Definition
-more efficacious c.f. morphine
-μ-agonist
-~20mins duration
-Admin: IV. Not suitable for single dose as v. short acting. Transdermal patches available
-clinical use: intra-op (CRI or intermittent boluses - not >1hr or accumulates and may slow recovery from anaes.) / post-op analgesia (CRI)
Side effects: more likely to cause bradycardia and resp. depression than morphine as more potent (dose dependent)
-will significantly dec. the amount of inhalent agent required if given intra-op |
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Term
| Buprenorphine (vet. license dogs, cats and horses) |
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Definition
-less efficacious c.f. morphine
-μ-partial agonist
-~6 hours duration (longest). Prob longer onset than morphine
-Admin: IM, IV, SC. Transdermal patch available. Sub-lingual admin in cats.
-clinical use: premed / post op analgesia
Side effects: unlikely to cause resp or CV depression |
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Term
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Definition
-less efficacious c.f. morphine and buprenorphine
-μ-partial agonist/antagonist. κ agonist
-~1.5 hours duration
-Admin: IM, IV, SC.
-clinical use: premed / post op analgesia
NB: also provides good sedation |
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Term
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Definition
-opiods are effective analgesics in dogs, generally also w. good sedation
-often MAC sparing effect (can dec. isoflurane - useful in CVS unstable patients)
Licensed drugs:methadone, pethidine, buprenorphine |
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Term
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Definition
-traditionally concern about potent opiod use in cats due to excitation beh. but weren't used well
-opiods are effective analgesics in cats
-less sedation c.f. dogs
-minimal MAC sparing effect
Licensed drugs:methadone (soon), pethidine, buprenorphine |
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Term
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Definition
-traditionally reluctance - may get locomotor activity e.g. boxing - people assume colic - this does not appear to be a problem
-don't sure MAC sparing effect due to boxing
-opiods are analgesic
-morphine can improve recovery quality
-buprenorphine provides good long duration analgesia
Use: morphone, buprenorphine (licensed), butorphanol |
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Term
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Definition
-expected pain severity - consider co-administered analgesic drugs
-ongoing plan for pain mgmt
-pre-, intra-, post-op i.e. time of admin
-ability to re-dose / duration of action
-routes of admin available |
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Term
| Animals in moderate-severe pain |
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Definition
-full opiod agonists e.g. morphine, methadone
-rel. long duration of action and can be given repeatedly or by CRI if still inadequate
-resp. and CV depression unlikely in animals in pain, esp if given IM
-use of multimodal techiniques may enablt to dose to decr. |
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Term
| Expected ongoing plan considerations |
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Definition
-if plan to use full opiod agonists intra- or post-op, it is not ideal to pre-med w. a partial agonist
-partial + full agonist is not additive
-partial has higher affinity for the μ receptor and so bind preferentially, preventing binding of the full agonist
NB: if give partial agonist and find it is inadequate, DO give full agonist - although response may not be as gr. as expected, it it better than waiting for partial to decr. |
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Term
| Time of administration of opiods considerations |
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Definition
-opiods given pre-op gen. need to be long lasting
-premed - buprenorphine and alpha-2-agonists are good combo - alpha-2-agonist often means don't need a full opiod agonist
-intra-op - gen. full agonist as want good analgesia - consider MAC sparing effect / alteration of inhalation agent
-Post-op - depends on pain severity and flexibility to redose e.g. not checked overnight / going home = long acting |
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