Analgesia and serum concentrations of extradural, subdural and intraperitoneal fentanyl in a rat model

Effect of the morphine/heroin vaccine on opioid and non-opioid drug-induced antinociception in mice

Pain is a common symptom in patients with opioid use disorder (OUD), which increases synthetic and illicit synthetic opioid abuse and even fatalities due to opioid overdose. Many FDA-approved drugs are available for the treatment of OUD, however, the use of these medications is limited, mainly due to the development of various side effects. Active vaccination is a new therapeutic approach but the resulting antibodies may compromise the use and efficiency of opioid and non-opioid drugs. In this study, we evaluated whether the antibodies produced by the morphine/heroin vaccine (M-TT) would alter the antinociceptive effects of opioid and non-opioid drugs. Female Balb-c mice were immunized with the M-TT vaccine. A solid-phase antibody-capture ELISA was used for monitoring antibody titer responses after each booster dose in vaccinated animals, followed by tail-flick testing. This study found that the M-TT vaccine did not affect the antinociception induced by different doses of morphine or the ability of non-opioid and synthetic opioid drugs to decrease thermal pain. Moreover, the combination of vaccination and naloxone increased the time-course of morphine antagonism relative to either vaccination or naloxone alone. These results suggest that the antibody titers generated by the M-TT vaccine 1) are capable of reducing morphine-induced antinociception and 2) are selective enough not to alter antinociception induced by non-opioid or synthetic drugs. These characteristics support its potential as a treatment agent for patients with symptoms of pain comorbid to OUD.

A rat model of chronic lumbar epidural catheterisation

PURPOSE

There are no rodent models of chronic epidural catheterisation which can induce clinically relevant analgesic effects of morphine (potency ratio of intrathecal:epidural = 10 to 30:1). The purpose of this study was to investigate a new rat model of chronic epidural catheterisation by comparing the analgesic effect of epidural and intrathecal morphine.

METHODS

In Sprague-Dawley rats, for epidural catheterisation, a skin incision and muscle dissection were made at T13 level in the midline. The intervertebral ligament was cut to insert an epidural catheter (polyethylene tube; outer diameter 0.14 mm) 2 cm caudally. The distal end of the catheter (0.61 mm) was passed s.c. to exit in the dorsal neck area. For intrathecal catheterisation, the atlanto-occipital membrane was incised to insert a catheter (0.61 mm) 8.5 cm caudally. The effects of morphine (1, 3, 10, 30, or 100 micrograms.10 microliters-1 intrathecally, and 30, 100, or 300 micrograms.5, 10, or 20 microliters-1 epidurally) on thermal escape latency were investigated by a hot box test. Behaviour and motor function were also tested.

RESULTS

A volume of 20 microliters induced greater analgesic effect than 5 and 10 microliters epidural administration. The ED50 of epidural morphine (94.1 micrograms) was 30 times more than that of intrathecal morphine (3.1 micrograms).

CONCLUSION

A new rat model of chronic epidural catheterisation is described, which provides a similar analgesic epidural: intrathecal potency ratio for morphine to that in humans when morphine is administered in a volume of 20 microliters.