The current presentation include mechanism involved in emesis and pharmacology of different emetics used clinically. Reference: Essentials of Medical Pharmacology, Sixth Edition, K D Tripathi.

1. EMETICS
Anusha Shaji, B.Pharm, M.Pharm
Assistant Professor
Department of Pharmacology
Nirmala College of Pharmacy,
Muvattupuzha, Ernakulam

2. Emesis
Vomiting occurs due to stimulation of the emetic (vomiting)
centre situated in the medulla oblongata.
Although nausea and vomiting may occur in a variety of
conditions
For example: motion sickness, pregnancy, and hepatitis
And are always unpleasant for the patient
The nausea and vomiting produced by many chemotherapeutic
agents demands especially effective management.
Nearly 70 to 80 percent of all patients who undergo
chemotherapy experience nausea or vomiting.

3. Several factors influence the incidence
and severity of chemotherapy-induced
emesis (figure 28.9)
Emesis not only affects the quality of life
But can also lead to rejection of
potentially curative antineoplastic
treatment.
In addition, uncontrolled vomiting can
produce dehydration, profound metabolic
imbalances, and nutrient depletion.

4. Mechanisms that trigger vomiting
Two brainstem sites have key roles in the vomiting reflex pathway.
The chemoreceptor trigger zone (CTZ) is located in the area
postrema and the vomiting center
CTZ is outside the blood-brain barrier, thus, it can respond directly
to chemical stimuli in the blood or cerebrospinal fluid.
The vomiting center, which is located in the lateral reticular
formation of the medulla, coordinates the motor mechanisms of
vomiting.
The vomiting center also responds to afferent input from the
vestibular system, the periphery (pharynx and gastrointestinal tract),
and higher brainstem and cortical structures.

5. Cytotoxic drugs, radiation and other g.i. irritants release 5-HT
from enterochromaffin cells → acts on 5-HT3 receptors present on
extrinsic primary afferent neurones (PAN) of the enteric nervous
system (ENS)
↓
Which connect with vagal and spinal visceral afferents to send
impulses to NTS and CTZ.
Released in large quantity, 5-HT may also spill into circulation and
reach CTZ.
It may as well be released from platelets by inflammatory
mediators.
However, 5-HT is not the only mediator of such signals: many
peptides and other messengers are also involved.

6. Mechanisms that
trigger vomiting

7. Emetics
These are drugs used to evoke vomiting.
1. Act on CTZ : Apomorphine
2. Act reflexly and on CTZ : Ipecacuanha
Vomiting needs to be induced only when an undesirable
substance (poison) has been ingested.
Powdered mustard suspension or strong salts solution may be
used in emergency.
They act reflexly by irritating the stomach.

8. Apomorphine
It is a semisynthetic derivative of morphine
Acts as a dopaminergic agonist on the CTZ.
Injected i.m./s.c. in a dose of 6 mg, it promptly (within 5 min)
induces vomiting.
It should not be used if respiration is depressed, because it has
inherent respiratory and CNS depressant actions.
Oral use of apomorphine is not recommended because the
emetic dose is larger, slow to act and rather inconsistent in action.
Apomorphine has a therapeutic effect in parkinsonism, but is
not used due to side effects.

9. Ipecacuanha
The dried root of Cephaelis ipecacuanha contains emetine
It is used as syrup ipecac (15–30 ml in adults, 10–15 ml in
children, 5 ml in infants) for inducing vomiting.
It should be available in every household for emergency use.
It is less dependable than parenteral apomorphine and takes 15
min or more for the effect, but is safer.
It acts by irritating gastric mucosa as well as through CTZ.

10. All emetics are contraindicated in:
(a) Corrosive (acid, alkali) poisoning: risk of perforation and more
injury to esophageal mucosa.
(b) CNS stimulant drug poisoning: convulsions may be
precipitated.
(c) Kerosine (petroleum) poisoning: chances of aspiration of the
liquid (due to low viscosity) and chemical pneumonia are high.
(d) Unconscious patient: may aspirate the vomitus, because
laryngeal reflex is likely to be impaired.
(e) Morphine or phenothiazine poisoning: emetics are ineffective.