IN-DEPTH: COLIC


of mineral oil in the lungs can cause a fatal lipoid pneumonia.12,13 Psyllium is a bulk laxative frequently used in the treatment and prevention of sand colic. There is conflicting evidence as to its efficacy, however. Of twelve ponies with sand surgically placed into the cecum, six were treated with 1 g/kg psyllium and six were untreated. All were euthanized 11 days later with no significant difference in the amount of sand retrieved between the treatment and control groups.14 Another trial evaluating psyllium (0.5 g/kg), wheat bran (1 g/kg), and mineral oil (8 g/kg) also failed to prove increased sand evacuation rela- tive to untreated controls.15 More recent work showed that horses given psyllium (0.5 kg q12h) in addition to mineral oil (2 L q24h) had increased sand clearance relative to those administered mineral oil alone (51.0% vs 26.1% total sand removal)16 suggest- ing that psyllium may improve sand clearance. There is some concern that colonic flora will degrade psyllium after chronic exposure, thus decreasing any laxative properties. This has led to the com- mon practice of only feeding psyllium for 1 week out of every month for sand prevention in endemic ar- eas. The benefit, however, is that when fed rou- tinely (50–100 g daily), fermentation of psyllium by intestinal bacteria results in the production of short- chain fatty acids that may benefit healing of the colonic mucosa in cases of right dorsal colitis.17 Magnesium sulfate is frequently dosed at 0.5 to


1.0 g/kg enterally for treatment of impactions. Systemic absorption of MgSO4 is believed to be lim- ited; however, slight increases in plasma magne- sium have been noted.6 Renal excretion should prevent hypermagnesemia; however, magnesium toxicosis has been reported in dehydrated horses.18 Simultaneous administration of enteral magnesium sulfate with intravenous fluids is thought to pro- mote secretion of fluids into the intestinal lumen by increasing the intraluminal osmolality. However, as previously discussed, there is work to support that a balanced electrolyte solution given enterally is superior to IV fluids plus MgSO4 in promoting hydration of ingesta.2 Enteral MgSO4 (1 g/kg in 1 L water) is superior to either plain enteral water or IV fluid therapy at 5 L/h for 12 h in improving fecal water content.6 Dioctyl sodium sulfosuccinate (DSS) is an anionic surfactant, which decreases surface tension, thus, facilitating water penetration. Historically, it has been used to treat impactions at 4 to 8 oz in8Lof water; however, it is not superior to the use of mag- nesium sulfate and water.19 Toxicity (colic, diar- rhea) has also been reported at a dosage of 50 mg/kg, and DSS is, therefore, of questionable use when there are other safer alternatives. Activated charcoal and/or di-tri-octahedral smec-


tite (DTOS) may be used when the colic is thought to be due to ingestion of a toxin. Di-tri-octahedral smectite is a natural hydrated aluminomagnesium silicate that adsorbs positively charged organic cat-


ions in the intestinal tract. It is used to treat and prevent enteritis in a variety of species and is now frequently used for the prevention and treatment of colitis in horses. It was first reported to prevent lincomycin-induced colitis in four horses, specula- tively due to absorption of clostridial toxins.20 It has since been shown that DTOS effectively absorbs Clostridium difficile toxins A and B, C perfringens enterotoxin and exotoxins, Bacteroides fragilis toxin, and gram-negative endotoxin in vitro.21–23 DTOS does not inhibit the effect of metronidazole, which is fortunate as both drugs may be used simul- taneously for treatment of clostridial infections. Horses treated with DTOS after surgery for large intestinal disease had a significant reduction in the prevalence of postoperative diarrhea (10.8%) com- pared with negative controls (41.4%).24 In the pre- viously discussed research on cantharidin, rats administered activated charcoal or smectite had sur- vival times similar to the negative controls, suggest- ing that these treatments may be preferred over mineral oil in cases of blister beetle toxic- ity.11 Horses may also be exposed to toxins iatro- genically due to misreading of labels on gallon sized jugs. Propylene glycol has been accidentally ad- ministered to horses due to the similarity of the label to mineral oil. Propylene glycol toxicity can result in D-lactic acidosis with severe depression and ataxia or death.25,26 Isopropyl alcohol has also been accidentally administered resulting in central nervous system depression and colic. Supportive medical therapy, gastric lavage, and repeated ad- ministration of activated charcoal is advocated in these cases as significant amounts of isopropyl alco- hol and acetone are adsorbed by charcoal in vitro.27 Gastric and enteric phytobezoars due to persim-


mon ingestion may also be treated successfully with medical treatment. Intragastric or oral adminis- tration of carbonated cola or diet cola has been reported successfully.28 The mechanism of dissolu- tion is not well understood but is likely due to a combination of mucolysis, dissolution from carbon dioxide bubbles, and acidification.


4. Pain Management


The signs of pain seen with colic can be due to distension of a viscous, tension of the root of the mesentery, or inflammation. Pain management is an important part of managing colic as pain itself can cause motility inhibition. While many of the drugs used to treat colic may cause transient de- creased motility, the beneficial effects typically out- weigh those consequences. Multiple analgesic agents are often used for the treatment of colic: non-steroidal anti-inflammatory drugs (NSAIDs), opioids, and 2-adrenergic agonists (Table 1). As distension is a frequent source of pain, nasogastric intubation to relieve gastric distension may also be an important part of pain control. Cecal tro- charization may be performed in horses with marked large colon or cecal gas distension when


AAEP PROCEEDINGS  Vol. 60  2014 215


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