Antiemetics are a diverse group of drugs used to treat or prevent nausea and vomiting, including that associated with cancer therapy, anaesthesia and surgery, and motion sickness.
Antiemetics described here include: the dopamine antagonists metoclopramide and chlorpromazine hydrochloride; antihistamines such as dimenhydrinate, meclizine hydrochloride & promethazine hydrochloride; and the phenothiazine thiethylperazine maleate.
The choice of drug depends partly on the cause of nausea and vomiting. For example, hyoscine (see section 1.2.) or antihistamines are used in motion sickness where as dopamine antagonists, which act selectively on the chemoreceptor trigger zone, are ineffective for the treatment of motion sickness. Conversely, nausea and vomiting associated with cancer chemotherapy is often hard to control and special regimens have been devised including the use of metoclopramide in high doses and more recently 5 HT3 antagonist and ondanesetron.
The antihistamines may be slightly less effective than hyoscine against motion sickness but are often tolerated.
There is no evidence that any one antihistamine is superior to another but their duration of action and incidence of adverse effects (drowsiness, and antimuscarinic effects) differ. For example dimenhydrinate causes drowsiness more frequently; meclizine has a longer duration of action than scopolamine and most other antihistamines.
If a sedative effect is desired promethazine is useful.
A popular choice of antiemetic is metoclopramide which is effective against nausea and vomiting following surgery and chemotherapy and is also effective against radiation - induced nausea and vomiting. Combining metoclopramide with corticosteroids (such as Dexamethasone) can improve its antiemetic effect in chemotherapy - induced nausea and vomiting. Metoclopramide may cause acute dystonic reactions with facial and skeletal muscle spasms and oculogyric crises. These reactions are most common in the young (especially girls and young women) and the elderly; they occur shortly after the start of treatment and subside within 24 hours of drug withdrawal.
Antiemetics are unnecessarily and some times harmful when the cause can be treated, e.g. as in diabetic ketoacidosis, or in excessive digoxin or antiepileptic dosage.
Meclizine Hydrochloride
Tablet, 12.5 mg, 25 mg
Indications: -for the prevention and treatment of nausea, vomiting and/or vertigo associated with motion sickness; see also notes above.
Cautions: - warn the patients not to perform hazardous activities requiring mental alertness or physical condition; patients with angle closure glaucoma or prostatic hypertrophy bladder neck obstruction, coma, jaundice. See also Interactions.
Drug interactions: - alcohol, CNS depressants including barbiturates, tranquillizers.
Side effects: - drowsiness, fatigue and rarely blurred vision, dryness of mouth, nose and throat.
Contraindications: - in patients who are hypersensitive to it.
Dose and Administration
Adults & Children (>12 years of age): -
Motion sickness (prophylaxis & treatment) - Oral, 25 to 50 mg one hours before travel. Dose may be repeated every twenty-four ours as needed.
Vertigo (prophylaxis and treatment)- Oral, 25 to 100 mg a day as needed; in divided doses.
Storage: - at room temperature, in a well - closed container.
Dimenhydrinate
Tablet, 50 mg
Indications: - see under Meclizine Hydrochloride
Cautions: - patients should be cautioned against performing hazardous activities requiring mental alertness or physical condition; prolonged therapy may produce blood dyscrasia; in patients in whom anticholinergics may aggravate other clinical conditions (e.g angle-closure glaucoma, enlargement of the prostate gland); risk-benefit should be considered for the use of the drug to pregnant and nursing mothers; see also interactions.
Drug interactions: -alcohol, CNS depressants such as barbiturates, drugs with anticholinergic effects including tricyclic antidepressants, ototoxic drugs such as aminoglycoside antibiotics (Dimenhydrinate may mask the early symptoms of ototoxicity).
Side effects: - drowsiness (if it is excessive, dosage should be reduced), paradoxical excitement in children and occasionally in adults, headache lassitude, tinnitus, blurred vision, dryness of mouth and respiratory passage ways, palpitation, dizziness and hypotention.
Dose and Administration
Adults, Oral, 50 to 100 mg every four to six hours. Children (6-12 Years of age) - oral, 25 to 50 mg every six to eight hours as needed, not to exceed 150 mg per day. Children (2-6 years of age), Oral, 12.5 to 25 mg every six to eight hours as needed, not to exceed 75 mg per day.
Note: oral dosage forms used for motion sickness should be taken 30 minutes before motion
Storage: - at room temperature, in a well-closed container.
Promethazine Hydrochloride
Tablets, 10 mg, 25 mg
Elixir, 5mg/5 ml.
Suppository, 25 mg, 50 mg
Injection, 25 mg/ml in 1 ml and 2 ml ampoules
Indications: - control of nausea, vomiting, and vertigo of various cause, as a sedative and hypnotic, and as a common ingredient of cough and cold preparations; also see notes above.
Cautions: - see under Meclizine Hydrochloride, intravenous injection of promethazine hydrochloride must be given slowly and extreme care must be taken; should not be given by subcutaneous injection, avoid in porphyria.
Drug interactions: - see under Meclizine hydrochloride; epinephrine, extrapyramidal reaction causing medications, levodopa, metrizamide and monoamine oxidase (MAO) inhibitors including furazolidone, procarbazine, and selegiline.
Side effects: see under Meclizine Hydrochloride, and blood dyscrasias, sedative effect is more pronounced.
Contraindications: - patients who have exhibited hypersensitivity to the drug; also in those who have received large doses of CNS depressants and/or in those who are comatose, in epileptic seizures.
Dose and Administration
Antiemetic,
Oral, Adult, 25 mg initially, then 10 to 25 mg every 4 - 6 hours as needed.
Note: For motion sickness, the initial 25 mg dose should be taken one half to one hour before travel, and the dose repeated 8 - 12 hours later, if necessary.
Children (>2 years of age); 0.25 to 0.5 mg per kg of body weight every 4 to 6 hours or 10 to 25 mg every four to six hours as needed.
IM or IV, Adults, 12.5 to 25 mg every 4 hours as needed. Children (> 2 years of age); 0.25 to 0.5 mg per kg of body weight every 4 to 6 hours as needed.
Rectal, Adult, 25mg initially, then 12.5 to 25mg every 4 to 6 hours as needed. Children (> 2 years of age); 0.25 to 0.5mg per kg of body weight, or 12.5 to 25mg every 4 to 6 hours as needed.
Antivertigo agent,
Oral, Adult, 25mg 2 times a day as needed. Children (> 2 years of age), 0.5mg to 1mg per kg of body weight or 10 to 25mg 2 times a day as needed.
Rectal, Adult, 25mg 2 times a day as needed. Children (> 2 years of age), 0.5mg per kg of body weight, or 12.5 to 25mg 2 times a day as needed.
Storage: - Suppositories: store between 2 and 8°c, in a tight, light - resistant container. Tablet & Injection - at room temperature protect from light & from freezing
Metoclopramide Hydrochloride
Tablet; 10 mg, 25 mg
Suppository, 25 mg, 50 mg
Drop, 5 mg/ml
Injection, 25 mg/ml in 1 ml and 2 ml ampoule
Indications: -nausea and vomiting in gastrointestinal disorders and treatment with cytotoxics or radiotherapy; gastro-oesophageal reflux, gastroparesis; pre-medication and postoperatively, aid to gastro-intestinal intubation, nausea and vomiting in migraine; see also notes above
Note: In children (and in some countries, patients under 20 years); use is restricted to severe intractable vomiting of known cause, vomiting of radiotherapy and chemotherapy, aid to gastrointestinal intubations; pre-medication.
Cautions: - elderly, children and young adults; hepatic & renal impairment may mask underlying disorders such as cerebral irritation, avoid for 3 - 4 days after gastrointestinal surgery; pregnancy; breast feeding; parkinson disease; depression; porphyria; see also interactions.
Drug interactions: - alcohol, CNS depressants
Side effects: -extrapyramidal symptoms, tardive dyskinesia on prolonged use; hyperprolactinaemia; drowsiness, restlessness, dizziness, headache, diarrhoea, depression, hypotension and hypertension reported; rarely neuroleptic malignant syndrome; cardiac conduction abnormalities following IV administration.
Contraindications: - epilepsy; gastrointestinal hemorrhage, mechanical obstruction or perforation; pheochromocytoma.
Dose and administration
Nausea and vomiting, gastro-oesophageal reflux, gastroparesis:
Adult; Orally, or IM, or slow IV injection; Adult 10 mg 3 times daily; young adult 15 - 19 years (under 60 kg) 5 mg 3 times daily; child up to 1 year (up to 10 kg) 1 mg twice daily, 1 - 3 years (10-14 kg) 1 mg 2 - 3 times daily, 3 - 5 years (15 - 19 kg) 2 mg 2 - 3 times daily, 5 - 9 years (20-28 kg) 2.5 mg 3 times daily, 9 - 14 years (30 kg and over) 5 mg 3 times daily. (Usual maximum 500 micrograms/kg daily, particularly for children and young adults)
Pre-medication, by slow I.V., Adults 10 mg as a single dose.
Aid to gastrointestinal intubation, Orally, or IM or by Slow intravenous injection, Adult 10 - 20 mg as a single dose 5 - 10 minutes before examination; Young Adult (15 - 19 years) 10mg; child under 3 years 1 mg, 3 - 5 years 2 mg, 5 - 9 years 2.5 mg, 9 - 14 years 5 mg.
Storage: -at room temperature, protect from light.
Chlorpromazine Hydrochloride
Tablet, 25 mg, 50mg, 100 mg
Syrup, 25 mg/5 ml
Drop, 25 mg/ml
Injection, 25 mg/ml in 1 and 2 ml ampoules
Indications: - for the prevention and control of severe nausea and vomiting, other indications (see section 4.2)
Note: It should not be used for motion sickness
Cautions: - liver diseases, alcoholics, hypersensitivity, or in children, elderly or weak patients, during pregnancy and breast-feeding. It has a sedative effect. Advise patients to avoid driving and operating machines.
Drug interactions: - alcohol, adrenaline, piperazine, antacids, phenobarbitone or other CNS depressants.
Side effects: - drowsiness, postural hypotension, dry mouth, nasal congestion, may occur commonly.
Contraindications: - severe central nervous system depression, or severe cardiovascular diseases and hypotension.
Dose and Administration: -
Adults: Oral, 12.5 -25mg every 4 - 6 hours, as necessary.
Slow, deep I.M., 25 mg as a single dose, the dosage being increased to 25 - 50mg every 3 - 4 hours until vomiting stops; it is then given orally if necessary.
Children (6 month and over): Oral or slow, deep I.M., 0.55mg/kg every 6 - 8 hour as necessary.
Note: Patients should remain lying down for at least 30 minutes after injection.
Storage: - at room temperature. Protect from light and freezing.
Do not use if solution is markedly discolored or if a precipitate is present.
Thiethylperazine Maleate
Tablet, 6.5 mg
Suppository, 6.5 mg
Injection, 6.5 mg 1 ml in 1 ml ampoule
Indications: -for the control of nausea and vomiting of various etiologies.
Cautions: -caution should be taken in patients with extrapyramidal effects; children, pregnancy, elderly and breast-feeding. Advise patients not to drive vehicles and operate machineries.
Drug interactions: - alcohol, antacids, adrenaline, levodopa, quinidine, extrapyramidal reaction causing medications, Anticholinergics, barbiturates or other CNS depressants.
Contraindications: -severe cardiovascular disease, severe CNS depression, in comatose state and in those patients who have exhibited hypersensitivity reaction (example Dyscarsia, jaundice) to phenothiazine.
Side effects: - drowsiness or dizziness, dryness of the mouth, nose and throat, CNS depression, postural hypotension, seizures, headache, fever, blurred vision, tinnitus, peripheral edema of the arm, hands and the face.
Dose and Administration: -
Adults: Orally, Rectally,
IM - 10mg 1-3 times a day.
Children - safety and efficacy has not been established
Elderly - see adult dose.
Storage: -Thiethylperazine Maleate should be protected from light. It should be stored in tight, light-resistant container at room temperature
