A pregnant mare with a history of severe lameness had a long-term epidural placed that delivered morphine to make her more comfortable. The long-term use of the epidural caused no issues to the mare or her foal.
Drs. Alessandro Mirra, Jasmin Birras, Sabina Diez Bernal and Claudia Spadavecchia tested the theory, noting that in the past, morphine given as an epidural does have side effects, like slowing the movement of the gastrointestinal system. There is no equine-specific dosing information available, so the dosing protocol is typically established using personal experience and clinical reports. When other conditions are added in, like pregnancy, the outcome can be unpredictable.
The veterinarians inserted an epidural catheter when systemic pain treatment didn’t help the 20-year-old mare, who still had two months of pregnancy before her. They administered 0.1 milligrams of morphine per kilo of body weight every eight hours. A previous study had shown that one dose up to this amount didn’t affect the gastrointestinal tract.
The eight-hour doses of morphine continued for 14 days while the mare and her foal were carefully monitored. At day 16 the medication was changed to methadone as a morphine overdose was suspected. After 48 hours, the medication was swapped back to morphine. On day 21, the morphine deliver time was reduced to every 6 hours and ketamine was added to the dose.
On day 49, the foal was delivered and four days later the use of the epidural for pain control ended; the mare was then give a low dose of morphine and ketamine every eight hours via IM injection. The mare left the hospital at day 57 and pain control was continued at home.
During the mare’s pregnancy and after the delivery, the plasma values in the mare were similar to those of horses that had had morphine administered through other means at levels that did not produce side effects. There was no accumulation of morphine in the mare’s milk.
The researchers conclude that prolonged administration of morphine via epidural is a possibility for pregnant mares that have uncontrolled pain.
Read the study here.
Read more at HorseTalk.
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