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First published on 26 October 2009
Lab Anim
doi:la.2009.007160
© 2009 Laboratory Animals Limited

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Original Article

A preliminary investigation into the practicality of use and duration of action of slow-release preparations of morphine and hydromorphone in laboratory rats

M C Leach 1 , H E Bailey 2, A L Dickinson 1, J V Roughan 1 and P A Flecknell 1

1 Comparative Biology Centre; 2 School of Biomedical Science, Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK

Corresponding author: Dr M Leach. Email: m.c.leach{at}ncl.ac.uk

Significant advances have been made in our ability to assess pain and administer appropriate pain relief in laboratory animals. However, providing long-lasting analgesia using a route that does not involve animal restraint remains difficult. The objective of this study was to investigate whether oral administration of slow-release morphine or hydromorphone results in increased thermal nociception in laboratory rats. The results showed that 64 mg/kg morphine and 16 mg/kg hydromorphone induced comparable increases in foot withdrawal latencies for up to three hours postadministration; however, slow-release morphine increased response latencies for up to 11 hours. Whether these dose rates provide clinically effective pain relief has yet to be determined; however, these data suggest that using slow-release preparations could be an effective and highly practical method of elevating pain thresholds for a relatively prolonged period.

Key Words: Morphine • hydromorphone • rat • analgesia • oral • Hargreaves assay


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