Related Experiment Video
Updated: Aug 9, 2026
07:23
Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Morphine-associated pruritus after single extradural administration in a horse
John H Burford1, Kevin T T Corley
1Department of Veterinary Clinical Services, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire, UK.
Veterinary Anaesthesia and Analgesia
|April 26, 2006
Summary
Preservative-free morphine sulphate administered extradurally to a horse caused itching and local irritation, including hair loss and fluid discharge. These adverse effects highlight potential side effects of this specific analgesic administration route in equine medicine.
Area of Science:
- Equine medicine
- Veterinary pharmacology
- Animal pain management
Background:
- Extradural (epidural) administration of analgesics is used for pain relief in horses.
- Morphine sulphate is a potent opioid analgesic.
- Preservative-free formulations are sometimes preferred to minimize tissue reactions.
Observation:
- A 580 kg horse received a single extradural injection of 100 microg/kg preservative-free morphine sulphate.
- The catheter was placed in the first intercoccygeal space.
- The horse developed pruritus (itching) following the administration.
Findings:
- Focal irritation occurred 4-8 hours post-injection.
- Clinical signs of irritation included local alopecia (hair loss) over the gluteal muscles.
- Serum exudation (fluid discharge) was also observed at the injection site.
- These adverse effects were attributed to the extradural morphine administration.
Implications:
- This case suggests that preservative-free morphine sulphate, even at a low extradural dose, can cause localized adverse reactions in horses.
- Veterinarians should be aware of potential pruritus and local irritation when using this drug and administration route.
- Further investigation may be warranted to understand the mechanism and prevalence of these side effects.
