The femur
bone cancer pain model was developed by implanting mouse osteolytic
tumor cells (NCTC 2472) into the intramedulla of the femur in C3H/HeN mice. In vivo imaging analysis revealed that the implanted
tumor cells grew progressively over 14 days. Associated with the
tumor growth, guarding behavior, which was an indication of ongoing
pain, time-dependently increased. Limb use abnormality and
allodynia, which were indications of ambulatory and
neuropathic pain, respectively, also appeared. The
analgesic effects of
oxycodone and other
opioids, such as
morphine and
fentanyl, were evaluated at 14 days when all
pain-related behaviors clearly appeared.
Oxycodone (2-20 mg/kg, s.c.),
morphine (10-50 mg/kg, s.c.) and
fentanyl (0.05-0.2 mg/kg, s.c.) significantly reduced guarding behavior.
Oxycodone (5-20 mg/kg, s.c.) and
fentanyl (0.1 and 0.2 mg/kg, s.c.) significantly reversed limb use abnormality, but
morphine (5-50 mg/kg, s.c.) did not. Moreover,
oxycodone (5-20 mg/kg, s.c.) dose-dependently reversed
allodynia without affecting the
sham-treated mice.
Morphine (50 mg/kg, s.c.) and
fentanyl (0.075-0.2 mg/kg, s.c.) also reversed
allodynia, but
morphine (50 mg/kg, s.c.) tended to affect and
fentanyl (0.1 and 0.2 mg/kg, s.c.) affected the withdrawal threshold in
sham-treated mice. These results suggested that
oxycodone relieved not only ongoing
pain, but also ambulatory and
neuropathic pain, and that the
analgesic profile of
oxycodone could be different from that of either
morphine or
fentanyl.