Pharm: use of GI drugs
Segmentation, GI Motility, and Regulation
Segmentation and GI motility are influenced by the parasympathetic branch of the autonomic nervous system and by a set of hormones in the GI tract:
Gastrin
Secretin
Serotonin
Histamine
Prostaglandins
Vomiting is the forceful ejection of stomach contents; it is not merely regurgitation or heartburn. It requires the coordinated contraction of the stomach and diaphragmatic muscles to expel contents through the esophagus and mouth.
Hindgut fermenters cannot vomit (examples: rats, rabbits, horses).
The vomiting reflex is generated primarily in the brain:
Vomiting center
Chemoreceptor trigger zone (CRTZ)
Peripheral inputs can stimulate CRTZ via the vagus or glossopharyngeal nerves; higher brain centers can also trigger vomiting (sight, smell, pain).
Vomiting pathways and reflexes:
Peripheral sensory receptors stimulated by GI tract events (distension, toxins, irritation) can trigger vomiting via the vagus and glossopharyngeal nerves.
Vagus nerve stimulation from GI tract/heart pain or trauma can promote retching and vomiting.
Higher brain center input (fear, stress, excitement) can trigger vomiting (less common in dogs/cats than humans).
Vestibular input can cause motion sickness leading to vomiting (vestibular nuclei stimulate the vomiting center).
Endogenous vs exogenous triggers:
Endogenous: body-derived chemicals and hormones (e.g., dopamine, histamine) that stimulate vomiting.
Exogenous: external factors such as toxins, medications, disease (e.g., uremia in cats, radiation).
Common clinical implication: if a clinician prompts vomiting, CRTZ and/or higher centers are being stimulated; vomiting can be due to GI tract signals (vagus), heart pain, pain, smells, sights, or vestibular input.
In dogs/cats, four main pathways involve:
Peripheral sensory receptors
Stimulation of the vagus nerve
Stimulation of the glossopharyngeal nerve
Stimulation of higher CNS centers
Important clinical note: uremia is a notable endogenous trigger in cats; high urea levels can cause nausea and vomiting in felines.
Emetic Induction and Indications
Indication for emetics: to remove as much stomach content as possible after ingestion of toxins or potentially harmful substances.
Important clinical considerations before inducing emesis:
Assess initial and overall level of consciousness.
If the animal is semi-conscious or has risk of seizures, or if pharyngeal reflexes are depressed, avoid inducing vomiting due to aspiration risk.
If vomiting is induced, observe for potential aspiration pneumonia and have precautions in place.
Practical realities:
Emesis typically removes about of stomach contents; et an additional approach is needed to manage the remaining (e.g., dilution or binding agents like activated charcoal).
Hyper-motility medications may be used to speed transit and reduce absorption after ingestion.
Practical office considerations:
Documentation is critical for legal and medical reasons when advising owners on home care or when giving instructions for at-home emesis.
Do not give home dosing instructions for emetics without physician approval and documentation.
Emetic Drugs and Their Use
Apomorphine
Mechanism: Dopamine receptor agonist acting on CRTZ to induce vomiting (opioid-class relation; DEA Schedule C-II).
Administration:
Intravenous (IV) directly in the patient.
Some formulations can be crushed and mixed with sterile water for conjunctival (eye) administration; absorbed through the conjunctival sac and nasal lacrimal drainage, often leading to faster onset.
Efficacy and species differences:
In dogs, vomiting typically occurs within about after IV administration.
In cats, efficacy is variable; about a 50/50 chance of inducing vomiting when given via conjunctival or other administration routes.
Practical notes:
For conjunctival administration, flush the conjunctival sac well after dosing.
If given conjunctivally, there can be tear production and nasal drainage aiding absorption.
It is generally more reliable in dogs than in cats.
Reversal of opioid-like sedative effects can be achieved with antagonists such as naloxone in cases of oversedation or respiratory depression.
Safety considerations:
It is a controlled substance (C-II). Avoid in animals that cannot vomit or have high risk of aspiration.
Hydrogen peroxide (H2O2)
Mechanism: irritant that stimulates the stomach lining to induce vomiting (alkaline/irritating effects).
Key limitations:
Causes gastric/esophageal irritation that cannot be reversed; patient must ride out the irritation and healing occurs.
It should be used only within of ingestion to be effective; beyond that window, not useful and risks outweigh benefits.
Safety and home use caveat:
Do not instruct owners to administer at home without explicit professional guidance; legal documentation is required.
Ziozane (listed in transcript as an emetic agent)
Mentioned as one of the emetic options in some practice contexts; not elaborated in depth here.
Roparinol / Riparinol / Klevitrin (emetic options)
Roparinol is discussed as an emetic option that emerged in clinics about three years prior to the discussion. Some clinics like it; others are less convinced about its efficacy.
Klevitrin is a trade name; Riparinol is the generic name; Roparinol the other listed form.
Practical note: variability in efficacy across clinics; not universal as a first-line choice.
Xylazine (Xyvazine) for cats
Often the best option for inducing emesis in cats; labeled as an emetic option in cats.
Pharmacology: alpha-2 agonist; provides significant sedative effects.
Reversal: sedation effects can be reversed with atipamazole (ATM) or tolazoline if needed.
Dexmedetomidine (Dex) as an antiemetic/inducing agent
Mentioned as a potential option, sometimes used off-label in cats for emesis; not labeled for this purpose.
Off-label use requires caution and justification; consider pharyngeal reflex integrity to avoid aspiration.
Serum of EPICAT (cathartic emetic extract)
Not recommended due to significant risks: cardiotoxicity and delayed onset (could take around to stimulate vomiting).
It is irritating to the stomach and carries a risk of cardiac side effects; generally avoided when safer options exist.
Practical note on emetic choices
If the ingestion involved a toxin with known packaging, bring the package to the clinic to estimate dose/poison and toxic component.
For chocolate ingestion: the toxicity depends on chocolate type; sweeter chocolate is less acutely toxic per ounce, whereas baker’s chocolate is more toxic per ounce due to higher theobromine/caffeine content.
In dogs, chocolate toxicity can present with vomiting, restlessness, and lethargy; in cats, chronic and acute vomiting are common presentations.
In practice, not all vomiting is due to toxins; dietary indiscretion, GI disease, or systemic disease can also cause vomiting.
Veterinary Vomiting in Dogs and Cats: Practical Patterns and Examples
Dogs:
Acute vomiting commonly due to dietary indiscretion, garbage gut, or ingestion of non-food items (deer carcass, roadkill, killed animals, rabbits, etc.).
Food-related causes include true food allergies; pruritus (itching ears, paws) is a major sign of food allergy in dogs, not necessarily gastritis.
Drug-induced vomiting can occur; liver or kidney disease and Addisonian crisis can cause vomiting.
Chronic motility issues and obstruction (segmentation issues, pyloric outflow obstruction) can cause chronic vomiting.
Foreign bodies and neoplasias can cause obstruction and vomiting.
Megaesophagus is common; the appearance of vomitus can indicate whether food is still in the esophagus or has reached the stomach.
Cats:
Cats can have both chronic and acute vomiting; typically more vocal when they sense it is imminent.
Cats often seek out soft or difficult-to-clean surfaces to vomit on (e.g., beds, carpets) due to hygiene and comfort considerations.
Three common vomiting patterns in cats: white foamy vomitus, yellow bile-containing vomitus, and clear vomitus; color hints at possible underlying disease processes:
White foamy vomit is associated with systemic/metabolic conditions (e.g., hyperthyroidism, kidney disease, liver disease, diabetes, pancreatitis).
Yellow bile-containing vomit may indicate biliary or GI stasis issues (not explicitly detailed in transcript, but color-coded guidance given).
Clear vomit can occur with various GI disturbances; often indicates recent or ongoing irritation.
GI lymphoma should be considered in older cats with chronic vomiting, along with inflammatory bowel disease (IBD) and hyperthyroidism.
Heartworms: even a single worm in the heart can be deadly for cats; dogs may tolerate a single worm for years, but cats are highly sensitive.
Other important clinical clues in vomiting:
The quality of vomitus (liquid vs chunky vs food that is digested vs not digested) helps localize the problem (esophageal vs gastric involvement).
If food looks like a sausage-like tube, it may indicate megaesophagus with esophageal stasis; most vomiting in dogs is in a pile rather than a sausage shape.
Owners should be encouraged to provide photos or descriptions if the vomit cannot be brought to the clinic; pictures can help assess the pattern when the animal has eaten.
If blood is present, note whether it is bright red (fresh) or dark (digested); both have different implications and require different workups.
Common exam takeaway: ask about the vomitus appearance, onset, accompanying signs (diarrhea, lethargy, appetite, thirst), recent diet changes, access to toxins, medications, and exposure to potential poisons.
Chronic vs Acute Vomiting: Causes and Diagnostic Clues
Acute vomiting causes:
Dietary indiscretion, access to garbage, ingestion of carcasses (deer, calves), roadkill, small animals (rabbits), or other non-food items.
Food adverse reactions or true food allergies (itching ears/paws as a sign).
Drugs or medications; liver or kidney issues; Addisonian crisis.
Acute gastritis or inflammation.
Chronic causes of vomiting:
Chronic motility disorders (segmentation, pyloric outflow obstruction).
Inflammatory GI diseases (IBD), inflammatory gastritis.
Foreign bodies, chronic foreign material, or neoplasia.
Other important cat-specific conditions:
Hyperthyroidism in cats can present with vomiting.
GI lymphoma is a key consideration in older cats with chronic vomiting.
Megaesophagus and regurgitation considerations:
Not all vomiting is vomit; regurgitation can be mistaken for vomiting; megaesophagus can cause food to be expelled in a sausage-like pattern if the esophagus is the source.
Practical Clinical Considerations and Safety
Owner counseling and documentation:
It is essential to document the exact instructions given to owners if home measures are advised (e.g., use of home emetics).
Clarify that certain emetics cannot be safely used at home and require veterinary supervision.
Safety and legal considerations:
Many emetic agents require veterinary oversight; mismanagement can lead to aspiration, esophageal/esophageal burns, or cardiotoxicity.
For home use, many clinics require explicit documentation and instructions; avoid giving dosing instructions without clinical direction.
Observational notes during vomiting:
Expect hypersalivation, foaming at the mouth, restlessness, and anxiety as part of the vomiting process.
In end-stage toxicity, signs can worsen; be prepared for aspiration risk and respiratory depression.
Post-emesis care:
After emesis, monitor for dehydration, electrolyte disturbances, and continued GI irritation.
Activated charcoal or dilution strategies may be used to limit additional absorption of toxins.
Quiz and study context:
The session will include review content on antibiotics, antivirals, and antifungals; a quiz is planned to cover these in relation to the prior PowerPoint materials.
Quick Reference: Practical Clues for Clinicians
If you suspect toxin ingestion with clear packaging information, document weight and amount to estimate toxicity.
When a dog eats chocolate, the toxicity risk is related to the chocolate type; baker’s chocolate is more toxic per ounce than milk chocolate; white chocolate is the least toxic.
Color cues in vomitus can guide differential diagnosis in cats and dogs; white foamy indicates possible systemic disease; yellow bile suggests biliary/enteric issues; clear indicates GI irritation or earlier stages.
Cats with chronic vomiting should trigger evaluation for hyperthyroidism, GI lymphoma, and IBD; hyperthyroidism is common in cats and can contribute to vomiting.
The statement that “900% of the time” a dog vomits is likely hyperbole or a transcription error; practically, vomiting is highly variable and depends on the underlying cause and stimulus.
Summary Takeaways for Exam Preparation
Vomiting is a brain-mediated reflex with multiple triggers (peripheral GI signals, CRTZ, vestibular input, higher CNS centers).
Four major pathways for emesis: peripheral sensory receptors, vagus nerve, glossopharyngeal nerve, and higher CNS/vestibular inputs.
Emesis-inducing drugs have specific mechanisms, routes of administration, species-specific efficacy, and safety concerns; never rely on a single drug across all cases.
In practice, expect about 80% stomach content removal with emetics; the remaining content may require binding agents or dilution.
Always consider aspiration risk and pharyngeal reflex integrity before inducing vomiting; documentation and owner communication are critical.
Understand common etiologies for vomiting in dogs and cats, including dietary indiscretion, toxins, GI disease, metabolic/endocrine disease, and neoplasia (with particular attention to cats and GI lymphoma, hyperthyroidism).
Be prepared to recognize vomiting patterns by color and consistency, and to correlate with potential systemic disease for cats.
Safety and legal considerations apply to home use of emetics; professional guidance is essential.
Key Equations and Quantities (LaTeX)
Emesis efficacy:
Removal effectiveness = of gastric content
Onset/dosing references:
Apomorphine IV onset: approximately in dogs
Conjunctival administration absorption via tear/nasal drainage
Hydrogen peroxide efficacy window: within of ingestion
Substance schedules:
Apomorphine is a controlled substance: Schedule
Emesis pharmacology keywords:
Dopamine receptor agonist; CRTZ target
Alpha-2 agonist in cats (e.g., xylazine) with reversal options: