Emetics

Emetics

Objectives

At the end of this lecture, student will be able to

•       Explain the difference between Regurgitation, Rumination and Bulimia

•       Describe the pathophysiology of vomiting

•       Explain about  emetics

Vomiting

•       Vomiting is often preceded by nausea and may be accompanied by retching

•       Vomiting can be a valuable physiological response to the ingestion of a toxic substance such as alcohol

•       It is also an unwanted side effect of many clinically used drugs, mainly cancer chemotherapy, opioids, general anesthetics.

It is important to differentiate vomiting from Regurgitation, Rumination and Bulimia.

Pathophysiology

•       Complex interactions between central and peripheral pathways.

•       The most imp areas involved peripherally are the gastric mucosa and smooth muscle (the enteric brain) and the afferent pathways of the vagus and sympathetic nerves.

•       The significant areas involved centrally are the area postrema, the Chemo receptor Trigger zone (CTZ), the nucleus tractus solitarus (NTS) and the vomiting centre.

     From pharmacotherapeutic point of view, the most imp aspect of this complex pathophysiology is the variety of receptors involved including:

• Histaminergic (H₁)
• Cholinergic (Muscarinic M₁)
• Dopaminergic (D₂)
• Serotonergic (5HT₃)
• Neurokinin-1 (NK₁) receptors

       In the clinical situation, this becomes target for various drugs directed at controlling the symptoms.

Emetics

•       The most commonly used emetics are Ipecac and Apomorphine.

•       Induced emesis is the preferred means of emptying the stomach in awake patients who have ingested a toxic substance or have recently taken a drug overdose.

•       Vomiting blood is often caused by ulcers, ruptured blood vessels, and stomach bleeding. It can also be caused by some forms of cancer

•       Emesis should not be induced if patient has CNS depression or has ingested certain volatile hydrocarbons or caustic substances

•       Frequent vomiting not related to any of these causes may be a symptom of cyclic vomiting syndrome.

•       This condition is characterized by vomiting for up to 10 days.

•       It is usually coupled with nausea and extreme lack of energy. It mainly occurs during childhood

•       Ipecac syrup(15-30 ml in adults, 10-15 ml in children, 5 ml in infants) is prepared from the dried rhizome and roots of Cephaelis ipecacuanha or Cephaelis
acuminata, plants from Brazil and Central America

•       Ipecac – stimulates the CTZ in the medulla & acts directly on the gastric mucosa – take w/ water (not milk or carbonation)

•       Onset in 15 to 30 min.   

•       Toxic if absorbed > give charcoal.

•       S/E:  Hypotension, tachycardia, chest pain, diarrhea, sedation, lethargy

•       Have alkaloid emetine as active principal ingredient

•       Acts directly on CTZ and indirectly by irritating gastric mucosa

•       The chemoreceptor trigger zone at the base of the fourth ventricle has numerous dopamine receptors

•        Serotonin 5-HT₃ receptors,opioid receptors acetylcholine receptors and receptors for substance P

•       Stimulation of different receptors are involved in different pathways leading to emesis, in the final common pathway substance P appears involved

•       It is cardio toxic if absorbed and causes cardiac conduction disturbances, atrial fibrillation, or fatal myocarditis

•       If emesis does not occur, gastric lavage using a nasogastric tube must be performed

•       Dehydration is the most common complication related to vomiting. Vomiting causes your stomach to expel not only food but fluids

•       It should be available in every household for emergency use.

•       Less dependable than parenteral apomorphine

•       Takes 15 min or more for its effect, but is safer

•       The vagal and enteric nervous system inputs transmit information regarding the state of the gastrointestinal system.

•       Irritation of the GI mucosa by chemotherapy, radiation, distention, or acute infectious gastroenteritis activates the 5-HT₃ receptors of these inputs.

•       Apomorphine, a derivative of morphine, acts as dopaminergic agonist directly on CTZ.

•       Injected i.m./s.c.  In a dose of 6 mg, induces
vomiting within 5 min.

•       Oral use not recommended as emetic dose is larger.

•       The CNS mediates vomiting that arises from psychiatric disorders and stress from higher brain centers

•       More effective if water is first administered before oral or s.c. dosing.

•       Excessive dosage may cause respiratory depression and circulatory collapse.

•       Opioid antagonists (naloxone) usually reverse the depressant actions of apomorphine.

•       Not frequently used as emetic.

Summary

•       Vomiting is a complex reflex activity.

•       Emetic drug or vomiting drug are those drug which is responsible for the vomiting.

•       Emetic drug is apply when an undesirable like poison has been injected.

•       When an individual has consumed certain toxic substances and must be expelled before absorption