In rabbits , IV methadone achieves the highest plasma concentrations compared with IM or SC administration [ 10 ] .
Hydromorphone
The effective dose range of hydromorphone is 0.1 – 0.2 mg / kg , with 0.1 mg / kg producing peak plasma concentrations at 8.3 min when administered by the SC route , with a half-life of 24.7 min [ 1 ] , with recommended repeat dosing every 1 – 2 hours . A recent study [ 11 ] has shown that SC hydromorphone at 0.2 mg / kg caused increased withdrawal latencies from a thermal test from 1 hour to 4 hours post injection ( compared with saline ), whereas there was no effect of SC buprenorphine ( compared with saline ) at 0.02 or 0.04 mg / kg .
Morphine
Morphine doses listed in formularies for exotic species range from 0.2 to 5 mg / kg SC or IM , every 2 – 6 hours [ 12 , 13 ] . Doses of morphine at 1 mg / kg SC and lower have been found to cause side effects of emesis and hypersalivation , thought to be due to nausea [ 1 , 7 ] .
Fentanyl
Fentanyl provides excellent analgesia for moderate to severe somatic and visceral pain [ 14 ] . Owing to its rapid onset and short duration of action , it is normally given as a CRI .
Opioid-related nausea
Opioid-related nausea and emesis have been reported in ferrets ( Figure 3 ). Therefore , administering maropitant or ondansetron before premedicating with certain full µ agonists , such as morphine or hydromorphone , is often recommended [ 7 ] . Addressing nausea is particularly important for ferrets , as they should be able to eat as soon as possible after a procedure to avoid hypoglycaemia .
NSAIDs
Meloxicam
Meloxicam selectively inhibits COX-2 , an enzyme responsible for the synthesis of the inflammatory mediators prostaglandins . Currently , the dose used in ferrets is similar to the initial dose for cats and dogs , namely 0.2 mg / kg every 24 hours [ 13 ] or 0.1 – 0.3 mg / kg every 24 hours [ 12 ] . However , there is no recommendation , as yet , that the dose should be reduced for ongoing maintenance in ferrets , as in cats and dogs .
Chinnadurai et al . [ 15 ] looked at the differences in plasma meloxicam levels between male and female ferrets . Meloxicam at 0.2 mg / kg SC resulted in plasma levels consistent with analgesia in other species , but the actual analgesic effect on ferrets was not studied . Interestingly , female ferrets showed faster drug elimination , a lower plasma concentration and a higher volume of distribution of meloxicam compared with male ferrets ( this study adjusted for weight differences ).
As in other species , meloxicam is contraindicated in patients with dehydration , hypovolaemia , hypotension , gastrointestinal disease or blood clotting issues . With surgical patients , NSAIDs are often given as the ferret regains consciousness , and once blood pressure and temperature have returned to normal [ 7 ] . Court [ 16 ] states that a ferret ' s glucuronidation pathway ( part of the drug metabolism process ) is similar to that of cats , so NSAIDs must be used with caution – although more research is needed .
There is a lack of information on long-term meloxicam use in ferrets . Pollock [ 17 ] advised that NSAIDs should be used with caution due to ferrets ’ propensity to develop stomach ulcers . van Oostrom et al . [ 18 ] advocate meloxicam as a valuable addition to the analgesic plan , but suggests that patients should be carefully monitored . Injectable meloxicam may be preferable to oral meloxicam , as this route may be associated with fewer gastrointestinal issues [ 19 ] .
NSAIDs should be used alongside a histamine type 2 receptor antagonist , such as famotidine [ 19 ] or ranitidine , to prevent gastric inflammation and ulceration . There is information to suggest that proton pump inhibitors , such as omeprazole , are superior to histamine type 2 receptor antagonists in controlling intragastric pH and treating gastroduodenal ulceration and erosion [ 20 , 21 ] . Sometimes these are used alongside other gastroprotectants .
Carprofen and aspirin
The use of carprofen and aspirin has been described [ 8 , 22 ] , but the authors have no experience of their use in ferrets .
Figure 3 . Nausea can be a problem with ongoing opioid administration in ferrets .
Adjunctive agents
Adjunctive agents are summarised in Table 1 ( page 17 ).
16 Veterinary Nursing Journal