Abdominal pain can be caused by multiple disorders and diseases. Intestinal dilation, distension, inflammation and ischaemia, and excessively filled organs such as stomach, uterus, or bladder lead to visceral pain. Somatic pain can be caused by abdominal wall disorders and surgery. Pain caused by peritonitis and pancreatitis can often not be clearly differentiated as visceral or somatic. Some disease processes, especially postoperative pain after hepatic or colonic procedures, are hard to control. Therefore, treatment of abdominal pain should address the underlying cause instead of using one standard protocol for all patients with abdominal pain.

Assessment of abdominal pain should be performed applying composite pain scales. This is especially true in diffuse visceral pain, where local pressure with palpation is often insufficient to cause reactions. Depending on the underlying cause, proper palpation of the abdomen is mandatory to assess pain. This should be done properly and slowly, without forced and fast movements, as these can cause non-pain related reactions. The potentially painful areas should be properly examined. For pancreatitis, the cranial abdomen should be palpated carefully. For kidney diseases, palpation of the kidneys helps to differentiate acute and chronic processes. Palpation of diseased organs is often painful in acute inflammation as this causes increase of organ volume and pressure on the capsule.

Standard analgesics for moderate to severe abdominal pain are opioids. For most abdominal procedures and postoperative analgesia µ-receptor agonists are used. These are not effective in controlling visceral pain like pain from gastric distension. Mu agonists lead to decreased propulsive intestinal motility, but may also cause increased intestinal and sphincter tone. Therefore, gastric and intestinal sounds often increase after opioid application. The increased sphincter tone may also decrease gastric emptying. The Sphincter of Oddi tone is also increased by µ-agonists. This may lead to decreased bile flow. Clinically, these motility and tone increases do not cause relevant problems. Some opioids such as morphine and fentanyl induce emesis, others as methadone may cause nausea without emesis. This has to be kept in mind if dealing with vomiting patients or patients not eating adequately.

Kappa-receptor-agonists like butorphanol provide analgesia for visceral pain. Due to its short half-life, butorphanol should be given as a constant rate infusion. Side effects are rare. Especially in older patients, sedation after administration of butorphanol may be severe and prolonged. Therefore, reduction of the dose by 50–75% is reasonable in these patients.

Tramadol has µ-agonist, serotoninergic, and NMDA effects, which explain its proposed analgesic properties. It is metabolized in the liver to the effective M1 metabolite. In some dogs, the metabolism is insufficient, and M1 is formed inadequately. Tramadol is used systemically but is also instilled into the abdomen for analgesia during laparotomy in humans. Side effects are dysphoria, centrally induced nausea and vomiting and constipation.

Ketamine is often included in analgesia protocols. Also, for abdominal pain, low dose ketamine provides analgesia. Side effects are minor. Due to the short half-life, it should be given as a bolus followed by a CRI. Commonly ketamine is used in combination with intravenous lidocaine. Lidocaine provides analgesia but has also positive effects on reperfusion injury and arrhythmias. The effect on gastrointestinal motility is questionable. In horses it improved gastrointestinal motility. Studies in dogs could not prove the same effect.

NSAIDs in abdominal pain are controversial. As commonly known, they can cause intestinal ulceration, vomiting, and diarrhoea, as well as kidney injury, especially in hypotensive patients. Due to these reasons NSAIDs should only be used if intestinal or kidney injury is excluded and the animal is normotensive. Just recently a new drug, grapiprant was launched. Due to its effect at the EP 4 receptor its potential for intestinal injury may be lower, compared to standard NSAIDs.

Metamizole is a pyrazolone-derivate, belonging to the group of non-acidic-non-opioid analgesics. In some countries it is named dipyrone. It has anti-inflammatory, spasmolytic, and antipyretic effects and also acts at the µ-opioid receptor. Studies in rats and dogs evaluated its effect on intestinal integrity and did not find any intestinal injury, even after using high doses of metamizole. There are no studies proving kidney injury after using metamizole in dogs and cats. Side effects of metamizole are salivation after application in cats and hypotension after fast intravenous application. In humans a reversible agranulocytosis is described after prolonged use. This side effect is, to date, not reported in veterinary patients. Due to the positive effects and mild side effects, the author uses metamizole often as a first line drug in cardiovascularly stable dogs and cats with abdominal pain.

Local anaesthesia of abdominal pain has also been described. Intraabdominal application of lidocaine in very painful patients via drains is used as well as epidural anaesthesia. Epidural anaesthesia is especially helpful in severe abdominal pain from pancreatitis or peritonitis. Care must be taken to ensure strict hygiene. As epidural catheters are used for continuous infusion of local anaesthetics or opioids, these catheters must be managed in a strictly sterile fashion.

As histamine release is involved in every inflammatory process, anti-histamines such as diphenhydramine and chlorphenamine are known to have analgesic effects. These drugs are rarely used in veterinary medicine as analgesics. But especially in cases where NSAIDs cannot be used, antihistamines have the potential to provide analgesia alone and increase NSAID or metamizole derived analgesia.

NK1 receptor-antagonists like maropitant have been shown to have an analgesic effect. As its main indication is antiemesis, it is often given in vomiting animals. Because it also decreases nausea and has analgesic properties, application should be considered in many patients with abdominal pain.

As pain is also an emotional experience and well-being is an important factor in the control of pain, non-medical treatment of abdominal pain is also mandatory. From human medicine we know that warming of the abdomen often helps to decrease the pain. An excessively filled stomach will also cause pain, discomfort, decreased mobility and decreased food intake. Therefore, it is helpful to empty a massively filled stomach by oro-gastric or nasogastric tubes. In general, the patient should be placed in a quiet environment and on soft and clean bedding. TLC may also improve analgesia in many patients.