GI DRUGS
1. EMETICS
-Drugs that produce vomiting with the intent of removing an ingested toxin before it can be absorbed.
-Must be given within 4 hours of ingestion to be effective.
-Do not use if animal is comatose, seizing, has depressed pharyngeal reflexes, in shock, dyspneic, has bloat/torsion, or if
substance ingested was caustic.
-Do not give to rabbits, horses, or many rodents
CENTRALLY ACTING EMETICS
-Act on the Chemoreceptor Trigger Zone and/or the Emetic Center
A. Apomorphine
-Morphine derivative, Class II controlled substance.
-Stimulates dopamine receptors in CRTZ
-Poorly absorbed orally, so ROA is IV, IM, or in tablet form in conjunctival sac
-Vomiting occurs within 10 minutes of injection, within 20 minutes of conjunctival application. Remember to
flush eye after vomiting is achieved.
-Not as effective in cats as it is in dogs
-Reversible with Naloxone
B. Xylazine (aka Rompun, Anased)
-Sedative (non-controlled) and anesthetic that stimulates alpha two receptors in the CRTZ and Emetic center.
-Very effective as an emetic in cats, not as effective in dogs
-IM injection that produces vomiting within 5 minutes
-Emetic dose is lower than sedative dose
-Reversible with Yohimbine
LOCALLY ACTING EMETIC
-Cause irritation of the GI mucosa
Hydrogen Peroxide
-Used as an emetic in dogs, cats, pigs, ferrets
-3% solution that can cause vomiting within 10 minutes when given orally.
-Can result in gastritis, aspiration
-Should fresh as it loses fizz after a few months
-1 tsp per 5 pounds. No more than 45 mL. May be repeated once after 15 minutes.
2. ANTIEMETICS
-Prevent or control vomiting
-Usually do not treat the underlying cause of vomiting.
-Given parenterally
A. Phenothiazine derivatives (Chlorpromazine- Thorazine)
-Blocks dopamine receptors in the CRTZ that may also directly inhibit the Emetic center.
-Tranquilizer, but antiemetic dose should not cause pronounced sedation.
-Lowers the seizure threshold.
B. Procainamide Derivatives (Metoclopramide- Reglan)
-Blocks dopamine receptors in the CRTZ.
- Prokinetic drug: increases gastric contractions and speeds emptying, strengthens cardiac sphincter tone.
-DO NOT GIVE WITH GI OBSTRUCTION
-More effective in dogs than cats.
C. Antihistamines (H1 blockers: Diphenhydramine- Benadryl, Dimenhydrinate- Dramamine)
-To be used as antiemetics when vomiting is caused by motion sickness or inner ear abnormalities.
-Inhibit vomiting by decreasing impulses sent from the vestibular apparatus by blocking H1 receptors at the
CRTZ.
-More effective in dogs than cats.
-May cause sedation.
-Although injectables are available, oral dose can be given prophylactically.
D. Serotonin Receptor Antagonists (Ondansetron- Zofran, Dolasetron (Anzemet)
-Also called 5-HT3 receptor antagonists, these drugs block serotonin (a neurotransmitter) receptors on the vagus
nerve and in the CRTZ.
-Pricey, but may be worth it for short-term treatment.
E. NK-1 Receptor Antagonists (Maropitant citrate- Cerenia)
-Inhibit the binding of Substance P (a neuropeptide) to neurokinin receptors in the Emetic center.
-Injectable form is approved for use in both dogs and cats. Oral form is for dogs.
-Injection may be painful.
-Can be given prophylactically to prevent motion sickness (without causing drowsiness), but also used to treat
vomiting from other causes.