8 Equine GI Drugs

• Colic is the most common GI disease in horses
• Colic refers to abdominal pain in horses, the most common source being the GI tract. The term can also refer to "gas colic" and impactions

Drugs for Colic

• Fecal softeners can be used to treat impactions
• Fecal softeners can be used to treat gastrocolic reflex
• Analgesics and drugs to improve motility are also used

Objectives

• Become familiar with products given via NG tube in horses
• Including fecal softeners
• What drugs that are appropriate (or not) for analgesics to treat colic
• Motility drugs in horses, when to use them, and their side effects

Colic Work Up

• Passing a nasogastric tube helps check for gastric fluid
• "Net" nasogastric reflux happens when more fluid comes out than goes in
• Medications can be administered via NG tube if there is no net reflux
• Fecal softeners are an example of a medication administered via NG tube

Fecal Softeners

• Mineral oil softens stool
• Dioctyl sodium sulfate “DSS” softens stool
• MgSO4 (Epsom Salts) softens stool in horses

Chester Case Study

• Chester is a horse with mild colic for 2 days
• Chester is presenting in winter when water is cold
• Chester has a temperature of 100 F
• Chester's heart rate is 60 bpm
• Chester has a large colon impaction upon rectal examination
• Chester's PCV is 50% and TP is 7.4 gm/dl
• Veterinarians should consider which fecal softener to use

Large Colon Impactions

• Large colon impaction is due to lack of water intake
• Water can be administered via NG tube in 4 to 5 L increments at once
• Water & Electrolytes can be administered multiple times via NG tube
• Large volumes of Water & Electrolytes (4 to 5 L q hr) can be administered every 60 minutes, ensuring no reflux

Water and Electrolytes for Impactions

• Administering Water and Electrolytes is inexpensive
• Administering Water and Electrolytes treats the primary cause by providing fluid in the GIT
• Water & electrolyte treatment is better than oral MgSO4 + IV fluids
• Large volumes can be administered via the NG tube

Water and Electrolytes Cons

• Water & electrolytes usage is contraindicated if the horse has gastric reflux
• It can result in colic due to the large volumes
• It can be difficult to pass the NG tube in some horses
• Problems with the NG tube include it coming out, the horse is difficult to tube, and rupture of the pharynx/esophagus
• Large volumes of only water can cause electrolyte abnormalities

Details of Fecal Softners

• Mineral Oil should be used after rehydrating the horse
• Mineral Oil is easy to see when it passes
• Mineral Oil can cause death if it gets into the lungs
• DSS should be used after rehydrating
• DSS can help water penetrate the impaction
• DSS can be irritating to the gut
• MgSO4 should be used after rehydrating
• MgSO4 will pull water into the gut lumen
• MgSO4 is irritating to the gut and can cause Magnesium toxicity

Sand Impactions

• Psyllium, a "gel", picks up sand
• Correct dehydration first
• Use Psyllium in combination w/ mineral oil

Fecal Softeners

• The list of fecal softeners includes Water & Electrolytes, Mineral Oil, Epsom Salts, DSS, and Psyllium
• These are very inexpensive per treatment, roughly $10

Colic = Abdominal Pain

• Treatment goals are to provide analgesia keeping in mind some horses will require surgery
• Analgesics for equine veterinarians include NSAIDs, Tranquilizers/sedatives, and some others

NSAIDS

• Commonly used choices of NSAIDs are:
• Phenylbutazone (Bute)
• Flunixin meglumine (Banamine)
• Ketoprofen
• Firocoxib (Equioxx- specific Cox-2)

Flunixin Meglumine

• Is an FDA approved non-selective Cox inhibitor for horses
• Used to treat Colic & M/S pain
• Most efficacious NSAID when dealing with visceral pain
• Comes in Injectable or Oral product
• Dosage is 1.1 mg/kg IV, IM, or oral

Flunixin Meglumine Advantages

• Most efficacious NSAID for colic
• Provides Long lasting analgesia for 12 hours
• Will take 10-20 minutes to be effective
• Provides Mild to moderate analgesia (12 hours)

Flunixin Meglumine Disadvantages

• Toxicity to the GI & renal system possible depending on duration, dose and if combining with NSAIDs, dehydration
• Intramuscular Administration risks Clostridial myositis

Additional NSAIDs

• Phenylbutazone and Ketoprofen, are generally not as efficacious with GI pain
• Firocoxib (selective Cox-2) exists as oral & IV preparation
• Firocoxib has a long half-life (24 hrs) and requires a loading dose
• Some will use Firocoxib for colic

Formulations of Flunixin Meglumine

• Available as Injectable = $30/100 ml (10 doses)
• Oral paste = $30 = 3 doses
• Injectable is preferred as it has faster absorption than Oral paste

Sedatives for Colic

• Alpha-2 agonists include Xylazine and Detomidine
• Opioids include Butorphanol
• Acepromazine

Xylazine

• Xylazine is immediate acting (1-3 minutes)
• Xylazine provide a High level of analgesic
• Xylazine has a Short duration (15-20 minutes)
• Xylazine provides Sedation as well (i.e. technical skills passing a NG tube, rectal palpation)
• A disadvantage of Xylazine is decreased GI motility

Detomidine

• Detomidine is immediate acting
• Detomidine provides a high level of analgesia
• Detomidine has a longer duration than xylazine
• It can be used when surgery is not an option or during long trailer rides for a painful horse
• Detomidine is not the first choice in emergency situations

Opioid Drugs

• Butorphanol: Mixed agonist/antagonist is used in combination with alpha-2 agonist
• Butorphanol has a longer duration (10-90 minutes) than just xylazine and helps keeps feet on ground" better than xylazine
• A disadvantage of Butorphanol as it is a Controlled drug (must keep records) and Adverse effect on GI motility

Acepromazine

• Acepromazine is a sedative but not an Analgesic
• Acepromazine is also alpha-antagonist that causes Vasodilation and Hypotension
• Acepromazine is not a good choice for colic in horses

Usage Considerations for Sedatives

• Xylazine is injectable only and costs $1-2/dose
• Butorphanol is injectable only and costs $4/dose
• Detomidine can be administered via injectable or sublingual for $15-$25/dose (IV)
• Sublingual Detomidine preparation is not as profound of analgesia
• Detomidine has a Long lasting effect (hours) but this is not ideal in most colics

Fire Case Stuyd

• Fire is one example of how to treat a horse with Mod-severe colic over 1 hour with a HR of 80 bpm
• First administer Flunixin meglumine with a 10 ml = 1.1 mg/kg dose
• Then administer Xylazine 150 mg and 5 mg butorphanol
• Once the horse wakes, Banamine should then be effective

Promotility Drugs

• Colic is a common problem in horses and Promotility drugs can provide aid, but they are not always used
• Those that require Post-operative ileus
• Those showing Anterior enteritis

Post Operative Ileus

• Postoperative Ileus is usually strangulating small intestinal lesion, like Strangulating lipoma
• It is a common problem
• Refluxes are typically 50-70 L/day for Many days, leading to high costs

Anterior Enteritis

• T = 103 F; HR = 70 bpm
• Patients show a Red mm with 15 L of fetid brown reflux
• Caused by an Inflammatory condition of SMI
• Typical Refluxes are 80 L/day for 5 days, leading to high costs

Promotility Drugs Usage

• The choice to use Promotility drugs is not a common "first line of therapy"
• Used only in select situations like Post-operative ileus and Anterior enteritis
• Do not use when unsure of diagnosis

Examples of Promotility Drugs

• Lidocaine
• Cholinergic Drugs
• 5-hydroxytryptamine receptors (serotonin)
• Motilin agonist

Lidocaine

• Lidocaine is Very commonly used for ileus of the small intestine
• There are conflicting studies about Lidocaine
• The Mechanism of action is unknown, but Inhibiting sympathetic response, provides an analgesic and is anti-inflammatory

Lidocaine Dosing

• Using 2% Lidocaine: Must give an IV bolus (loading dose of 1.3 mg/kg (give slow)
• It must be given as a CRI of 0.05 ug/kg/min with a fluid pump
• The Drug is rapidly cleared once stopped

Promotility Lidocaine Advantages

• Provides potential benefits with analgesia, anti-inflammatory and pro-motility
• Colic has not been reported as a side effect

Promotility Lidocaine Disadvantages

• Narrow therapeutic index allows Toxicity (which is common) and CNS excitement
• Toxicity use is Not practical in field setting
• Cost of therapy is $60/day (450 kg horse) for lidocaine
• Cost of ICU (fluid pump) = $100/day

Cholinergic Drugs

• Bethanechol = muscarinic receptor agonist that you Give SQ
• Bethanechol Stimulates gastric emptying (biggest use)
• Bethanechol can also lead to increased salivation & colic
• Neostigmine = inhibits acetylcholinesterase that you Give SQ
• Neostigmine Stimulates motility of large colon but is Not recommended for small intestine or stomach and Colic can result

5-Hydroxytryptamine Receptor Agonist

• Metoclopramide: Best used by a CRI allowing small intestinal motility, however CNS excitement (severe) is possible
• Cisapride had Fewer side effects but was Taken off market

Motilin Agonist

• Motilin will Stimulates release of Ach from enteric neurons
• Erythromycin use IV (BID) – use very small doses, stimulates a small intestinal motility causing severe colitis to be reported

Motility Drugs Studies

• How are they usually studied in Normal horses?
• Have a Clinical impression but They do not work well with pathologic states
• Some carry significant complications like (colic)
• Lidocaine is used a lot with Benefits beyond just promotility...