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Effects of Antiemetic Drugs

Antiemetic drugs are used to treat or prevent nausea and vomiting (N&V) due to pregnancy, chemotherapy, anesthesia, toxins, gastrointestinal illness and many other causes. Several classes of drugs may be used as antiemetics. Mechanism of action and side effects vary among agents.

  1. Antacids and Other Over-the-Counter Remedies

    • Over-the-counter antacids may be useful in treating mild nausea, but are not often successful against vomiting. Magnesium, calcium or aluminum-based antacids coat and soothe the stomach, but can cause diarrhea or constipation. Other types of antacids, such as famotidine (Pepcid AC) or ranitidine (Zantac 75), may also be helpful in controlling mild N&V and have few side effects beyond headache or diarrhea.

      A special mixture of dextrose and fructose, marketed as Emetrol, may be used for mild, infrequent nausea or morning sickness. Side effects of Emetrol are minimal but may include diarrhea or stomach discomfort with higher doses. Emetrol should be used with caution in diabetics as it may increase blood sugar.

    Antihistamines/Phenothiazines

    • Histamine is a chemical compound involved in the body's response to outside stimuli, including toxins, pathogens, allergens and fight-or-flight situations. Blocking histamine may help relieve N&V by calming this response. Antihistamines, such as diphenhydramine (Benadryl), dimenhydrinate (Dramamine) and meclizine (Bonine, Antivert), are particularly useful in treating N&V related to motion or posture. Drowsiness is a major side effect. Dizziness, headache, dry mouth and mucus membranes, constipation or urinary retention may also occur.

      Phenothiazines are a subset of antihistamines used to treat N&V. The most common drug in this class, promethazine (Phenergan), has side effects similar to those of other antihistamines. Mild rash, sedation, photosensitivity or involuntary muscle spasm may occur as well.

    Serotonin Receptor Antagonists (5-HT3 RAs)

    • 5-HT3 RAs inhibit a specific subset of serotonin receptors in the brain and are beneficial in the treatment of many kinds of N&V, including N&V from chemotherapy. Ondansetron (Zofran) and granisetron (Kytril) are commonly prescribed 5-HT3 RAs and are well tolerated with few side effects beyond fatigue or headache. Less often, drowsiness, dizziness, anxiety, constipation and itching may occur.

    Dopamine Antagonists

    • These agents act on portions of the brain involved in the N&V response by blocking dopamine receptors. Haloperidol (Haldol) and droperidol (Inapsine) are two agents in this class and may cause involuntary muscle movement and sedation as primary effects. Cardiac arrhythmias associated with droperidol administration have reduced its use in common practice.

      Metoclopramide (Reglan) is effective at treating many types of N&V, and was considered the "gold standard" of chemo-induced N&V treatment until the discovery of 5-HT3 RAs. Metoclopramide blocks dopamine receptors while also promoting the movement of stomach contents into and through the bowel. Side effects include drowsiness, restlessness, fatigue, involuntary muscle movements and diarrhea.

    Benzodiazepines (BDZs)

    • These relatives of diazepam (Valium) are useful in the prevention of psychogenic N&V---nausea and vomiting associated with a previous N&V episode or stimulus. For example, a chemotherapy patient recognizing his oncologist at the mall may experience psychogenic N&V. Lorazepam, or Ativan, is commonly prescribed for this purpose. Side effects of BDZs include sedation, dizziness, disorientation and mild respiratory depression. Amnesia may occur with BDZs, but is typically confined to recall of events immediately following drug administration. This effect can benefit anxious cancer patients as it may inhibit memory of actual chemotherapy treatments.

    Cannabis Derivatives

    • Dronabinol (Marinol), or THC, the primary active compound in marijuana, has medicinal use in chemotherapy-induced N&V. Side effects include drowsiness, dizziness, mood changes, paranoia, euphoria, time distortion, hallucinations and hunger.

    Hypersensitivity

    • As with any medication, allergic response is possible. Patients who experience symptoms of allergic, reaction such as difficulty breathing or swallowing, rash, itching, hives or swelling while taking antiemetics, should seek urgent medical care.

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