The use of maropitant to prevent vomiting induced by epidural administration of preservative free morphine through an epidural catheter in a dog.

A male neutered Labrador, aged 8 years and 9 months, weighing 26.6 kg was admitted with a 6-month history of chronic vomiting and weight loss. Vomiting had been unresponsive to symptomatic treatment with bland diet, probiotics and sucralfate. Physical examination was largely unremarkable. Haematology revealed moderate lymphopaenia (0.564 · 10 L) and mild anaemia (haematocrit 25.5%) with moderate evidence of regeneration. Biochemistry revealed mild hypoalbumineamia (26.2 g L) and hypoglobulinaemia (14.7 g L). Further diagnostic procedures were performed under general anaesthesia. Laryngeal paralysis was noticed on induction of anaesthesia. Upper gastrointestinal endoscopy revealed a normal stomach but passage through the pylorus into the duodenum was difficult giving the impression of a diverticulum within the duodenum. Regurgitation of bile during the procedure was treated with omeprazole (1 mg kg). An exploratory laparotomy performed 5 days later confirmed the presence of a firm white lesion causing a stricture of the proximal duodenum at the level of the major duodenal papilla. A marginal excision of the anti-mesenteric section of this lesion was performed. Histopatology showed only evidence of chronic inflammation within the muscular tunics and extensive fibrosis. Post-operative analgesia was to be given by the epidural route. An 18 gauge epidural catheter (Mila International, KY, USA) was inserted at the level of the lumbo–sacral junction and advanced cranially until the level of the fourth lumbar vertebra. Preservative free morphine (Martindale Pharmaceuticals, UK), 0.1 mg kg diluted in 1.5 mL of sterile 0.9% sterile saline was administered over 2 minutes through the epidural catheter. This treatment was to be repeated every 12 hours. Intravenous (IV) morphine (0.2 mg kg) was given for immediate postoperative analgesia. The patient had an uneventful recovery from anaesthesia. Additional medical therapy consisted of ranitidine, 2 mg kg twice a day by mouth (PO), sucralfate, 5 mL twice a day PO and IV fluid therapy. The second epidural administration of preservative free morphine was given 12 hours later and the dog vomited immediately following injection. The elapsed time between the epidural injection and the vomiting was not recorded. The third epidural injection was given slowly, over 2 minutes, by the primary anaesthetist and again vomiting was observed 60 seconds after completion. The animal otherwise appeared slightly subdued but comfortable and responded to human interaction. He was able to urinate when helped into a standing position, but palpation of the bladder suggested that there was some urinary retention. Two hours before the next dose of morphine was due, maropitant (Cerenia; Pfizer Ltd, UK) 1.0 mg kg subcutaneously (SC) was administered and after this fourth epidural injection of morphine the dog did not vomit. Maropitant, 1.0 mg kg SC, was administered every 24 hours for the next 5 days. No emesis was observed after any of the following administrations of epidural morphine or during the rest of the hospitalisation period. The epidural catheter was removed after 75 hours and analgesia was then provided with tramadol, 50 mg twice a day PO. The dog was discharged 8 days after surgery. When hydrophilic agents such as morphine are administered in the epidural space, long lasting (up to 10–23 hours) analgesia is achieved with plasma concentrations below those known to be associated with clinical analgesia (Torske & Dyson 2000). The