antiemetic

Definition

Antiemetic drugs are drugs used to combat nausea and vomiting.

Purpose

Antiemetic drugs are used to prevent vomiting (emesis) in chemotherapy patients and postoperative patients. Aside from the difficulty of maintaining proper nutrition and a healthy weight, chronic vomiting can result in dehydration, which can be a medical emergency. Following are descriptions of many common antiemetic drugs in use as of 2004.

Description

Promethazine

Promethazine is also known as phenergan and mepergan. It is also used to treat motion sickness, reduce allergic symptoms, and for sedation. It is one of the drugs of the phenothiazine type. In addition to other qualities, it is an antihistamine.

Prochlorperazine

Prochlorperazine is also known as compazine. Like promethazine, it is a member of the class of phenothiazines. Unlike promethazine, however, prochlorperazine also belongs to the class of drugs known as antipsychotics, or neuroleptics. Antipsychotic drugs are used to treat psychoses and other psychiatric disorders. In addition to its use as an antiemetic and anti-psychotic drug, prochlorperazine is also used to treat non-psychotic anxiety.

Serotonin Receptor Antagonists

The serotonin receptor antagonists include granisetron (kytril), dolasetron (anzemet), and ondansetron (zofran). These drugs are used for postoperative nausea and emesis as well as nausea and vomiting associated with chemotherapy, and are often used in combination with a corticosteroid. Ondansetron is approved for nausea and vomiting associated with radiation therapy.

Neurokinin Receptor Antagonists

The Neurokinin receptor antagonists are a new class of antiemetics. Aprepitant (Emend) was approved in 2004 for use in cancer patients. It is used in combination with other antiemetics for relief of acute and delayed nausea and vomiting caused by high-dose chemotherapy, most often caused by the chemotherapy drug cisplatin.

Dronabinol

Dronabinol (marinol) is used to combat anorexia in AIDS patients, and emesis in cancer patients who haven't responded to other antiemetics. Marinol is the synthetic or extracted form of the active ingredient found in marijuana.

Other Antipsychotic (Neuroleptic) Drugs

The other neuroleptic (antipsychotic) drugs used to treat nausea and emesis are droperidol (inapsine), halo-peridol (haldol), chlorpromazine (thorazine), and perphenazine (trilafon). One other antipsychotic, triethylperazine (torecan or norzine), was used as an antiemetic, but is no longer widely available. Some of the antipsychotics are also used to treat aggressive or violent behavior or incontrollable hiccups (chlorpromazine). These drugs are similar to prochlorperazine in terms of their actions and potentially severe side effects.

Dosage

Promethazine

Promethazine is given in doses of 12.5 to 25 mg every 4 hours if injected into the muscle or as a suppository. As a syrup, 25 mg should be given every 4 to 6 hours. Doses for children vary by age, weight, and severity of condition.

Prochlorperazine

Generally, the dose is 5 to 10 mg, 3 to 4 times per day. However, the effect of medication varies widely from patient to patient, so the dose should be tailored to each individual. Prochlorperazine is available as a syrup, tablet, 25 mg slow-release capsule, and in injectable form.

Aprepitant

One 125-mg capsule is given by mouth one hour before chemotherapy begins. An 80-mg capsule is taken each morning for two days following the chemotherapy treatment.

Dronabinol

The effective dose of dronabinol varies widely from patient to patient and should be monitored and tested by the physician. The basic dose is 5mg/m2 given 4 to 6 times per day.

Precautions

Promethazine

Patients with cardiovascular disease or impaired liver function should either use this drug with caution or not at all. Children should also use this drug cautiously for two reasons. First, some side effects may suggest, or mask, underlying disease, such as Reye's syndrome. Second, large doses of this drug, or any antihistamine, may cause convulsions, hallucinations, or death in children. Patients taking this medication should not drive, operate heavy machinery, or engage in any hazardous activity while under the influence of this drug. This drug has not been established as safe for use during pregnancy, or in nursing mothers.

Prochlorperazine

Persons allergic to any other phenothiazine (such as promethazine) should not take prochlorperazine. Patients who have heart problems, glaucoma, or bone marrow depression should take this drug with caution, or not at all, and inform their physician of their condition. People who will be around high temperatures should also avoid this drug. In addition, those who experience seizures should be aware that administration of this drug makes seizures more likely.

Breast cancer patients may wish to avoid this drug because it increases levels of prolactin in the blood.

Increased prolactin may help some types of breast cancer to thrive.

Prochloroperazine, like promethazine, may mask symptoms of Reye's disease in children. It may also mask symptoms of intestinal obstructions or brain disease. In addition, children who are acutely ill, under two years of age, or under 20 pounds should not be given this drug.

This drug has not been established as safe for use during pregnancy and is found in the breast milk of lactating mothers. Therefore, caution should be used when administering this drug to pregnant women and extreme caution should be used when administering to nursing women.

Aprepitant

Patients should not drink grapefruit juice while taking aprepitant. The physician should be told if the patient is pregnant, breast feeding, or becomes pregnant while taking the drug.

Serotonin Receptor Antagonists

Patients with allergies to any drug in this category should not take any other drug in this category. Also, patients with hypokalemia, hypomagnesia, or certain heart problems should avoid taking these drugs. The effect of these drugs on the children or fetuses of nursing or pregnant mothers is not known, so they should be used with caution.

Dronabinol

Dronabinol is inadvisable for patients with a known allergy to either sesame oil or any part of the cannabis plant. Patients taking this drug should not drive, operate heavy machinery, or engage in hazardous tasks until used to this medication.

This medication also should be used cautiously, if at all, for persons with depression, mania, or schizophrenia, elderly patients, patients with cardiac disorders, and for pregnant and nursing women. It is especially inadvisable for nursing women, since marinol is concentrated in the breast milk.

Side Effects

Promethazine

Patients taking promethazine may experience a large number of side effects, including drowsiness, ringing in the ears, a lack of coordination, problems with vision, fatigue, euphoria, nervousness, tremors, seizures, a catatonic-like state, and hysteria. These effects are usually reversible. At high doses, patients may also exhibit extrapyramidal reactions. Extrapyramidal reactions can briefly be described as agitation (jitteriness, sometimes insomnia), muscle spasms, and/or pseudo-Parkinson's (a group of symptoms including, but not limited to, drooling, tremors, and a shuffling gait).

Patients may also experience rashes, asthma, jaundice, abnormally low production of white blood cells, and abnormalities in how fast or slow their heart beats. Patients may sometimes experience unusual side effects not known as typical for the medication they are taking. These should be reported to the physician.

Prochlorperazine

Prochlorperazine has many side effects, including low blood pressure, dizziness, blurred vision, skin reactions, and jaundice. Patients also may suffer jaw, neck, and back muscle spasms, slow or difficult speech, and difficulty swallowing, as well as rhythmic face, mouth, or jaw movements. However, the most severe side effects stem from damage to the brain after long-term use. These symptoms may be reversed by treating the patient with drugs effective in treatment of Parkinson's patients (except levodopa). A reduction or elimination in the amount of the antipsychotic medication may also be necessary to eliminate these symptoms.

Two other (rare) disorders, tardive dyskinesia and neuroleptic malignant syndrome (NMS), are also associated with antipsychotic drug use. Patients with NMS have high temperatures, rigid muscles, an altered mental state, and symptoms such as excessive sweating and irregular blood pressure or heart rhythm. Patients with NMS usually respond to treatment. Patients with tardive dyskinesia have involuntary movement of muscles in the chest, arms, and legs, or in the muscles in and around the face (including the tongue). Tardive dyskinesia may be irreversible.

Aprepitant

Side effects of aprepitant include fatigue, dizziness, stomach pain, nausea, hiccups, diarrhea, constipation, and loss of appetite. More serious, but less common, side effects have been reported, including hives, skin rash, difficulty breathing or swallowing, hoarseness, and swelling in the face, throat, tongue, lips, eyes, feet, ankles, or lower legs. If any of these more serious side effects occur, the patient should contact the treating physician immediately.

Serotonin Receptor Antagonists

Side effects include rashes, increased sweating, problems with taste or vision, flushing, agitation, sleep disorder, depersonalization, headache, fatigue, nausea, weakness, abdominal pain, constipation, diarrhea, hypertension, dizziness, chills and shivering, and dry mouth. Patients may also have abnormal liver function tests.

Dronabinol

Possible side effects are fatigue, weakness, abdominal pain, nausea, vomiting, heart palpitations, fast heart rate, facial flushing, amnesia, anxiety, an abnormal mental state, depersonalization, confusion, dizziness, and euphoria.

There are certain additional precautions and side effects associated with each of these drugs. Patients should be sure to notify their physician of any health concerns (including pregnancy) or medications they are taking. Patients should also ask about potential side effects for each individual medication before receiving any of these drugs.

Interactions

Promethazine

Promethazine interacts with central nervous system depressants, like alcohol and barbiturates. Therefore, the physician should be alerted to any medications the patient is taking, and doses of the drugs should be adjusted accordingly. Alcohol should be avoided. It has not been proven, but promethazine may interfere with the action of epinephrine.

Prochlorperazine

Like promethazine, prochlorperazine should be used cautiously, or not at all, with central nervous system depressants like alcohol and barbiturates. Prochlorperazine has also been shown to interact with anticonvulsant medication, guanethidene, propanolol, thiazide diuretics, and oral anticoagulants (like warfarin and coumadin).

Aprepitant

A physician can check the long list of possible drug interactions, which include possible effects on the action of certain chemotherapy drugs. Aprepitant also may interact with the blood thinner warfarin (Coumadin) and other popular drugs. The treating physician or pharmacist will need a complete list of other drugs the patient is taking before prescribing this antiemetic.

Serotonin Receptor Antagonists

These drugs may have very negative effects on the patient when combined with diuretics, anti-arrhythmia drugs, or high doses of anthracycline.

Dronabinol

Dronabinol interacts with the antiemetic prochlorperazine synergistically. Therefore, the use of these two drugs in combination results in a greater antiemetic effect. Patients taking central nervous system depressants, such as barbiturates or alcohol should notify their physician before taking marinol, since marinol may increase their effect. Although no drugs have been shown to interact with marinol, many drugs similar to marinol do interact with a number of other drugs, including central nervous system depressants such as alcohol or barbiturates, or drugs like flouxetine or disulfiram. Again, the physician should be alerted to any medications the patient is taking before beginning a course of dronabinol.