Maropitant is a neurokinin-1 (NK-1) receptor antagonist. The NK-1 receptor and its neurotransmitter substance P are involved in a number of cellular functions, including pain and inflammation. There are a number of studies looking at the potential analgesic effects of maropitant, as well as for its peri-operative anti-nausea and vomiting effects.
There is evidence to support the use of maropitant in dogs to reduce post-operative nausea and vomiting (PONV). It has also been successfully used to reduce vomiting and nausea associated with opioid administration as part of premedication, in particular associated with morphine and hydromorphone. Methadone, used more commonly in Europe does not induce vomiting, although post-operative nausea may be observed. To be effective, aim to administer at least 45-60 mins prior to opioid administration. It has become commonly used in brachycephalic dogs in this way, and for any animals with a history of previous PONV in the peri-anaesthetic period. In cats there is some similar evidence for the use of maropitant prior to sedation with alpha-2 agonist-opioid combinations to reduce the incidence of vomiting. In this scenario maropitant was successfully administered around 20 hours prior to sedation (PO or SC).
Two studies have documented increased food intake and quicker return to feeding when maropitant is used prior to anaesthesia in dogs.
There is further evidence supporting the ability to reduce isoflurane and sevoflurane requirements with the use of maropitant, which will be of benefit in cases where reduction in the dose dependent side effects of vasodilation, respiratory depression and reduction in cardiac contractility are required.
There is no strong evidence to support its use as a sole analgesic to date, with the studies looking at this application drawing varying conclusions.
The evidence for any anti-inflammatory properties is currently not strong, although there is an experimental study in a mouse model of acute pancreatitis which demonstrated a positive effect.
To summarise; the studies looking at anti-nociception all have differing methodology, which makes it more challenging to draw reliable conclusions. Unfortunately, to date there is no agreement between studies on the benefits of using maropitant as a peri-operative analgesic. Most importantly no studies documented any clinically significant adverse effects with the use of maropitant, and therefore it may be considered as part of a multi-modal analgesic plan. A number of studies have shown that maropitant will allow vaporiser settings (isoflurane and sevoflurane) to be reduced.
Based on this there is currently insufficient evidence to support maropitant’s use as part of a standard premedication protocol, but it does have a place on an individual case by case basis. With regard to the dose for administration, in the studies that used a 5mg/kg dose no increased benefit was documented, so it does not appear that increasing the dose (above 1mg/kg) is necessary.
This pain update was written by Carl Bradbrook.
Matt & Carl established Zero Pain Philosophy to provide educational resources to veterinary professionals enabling optimal management of pain.
Matt Gurney is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and works at Anderson Moores Veterinary Specialists. Matt is President of the European College of Veterinary Anaesthesia & Analgesia.
Carl Bradbrook is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and is President of the Association of Veterinary Anaesthetists. Carl works at Anderson Moores Veterinary Specialists.