Promethazine Vs. Ondansetron: Drug Comparison

Promethazine is the active ingredient in the brand-name medication Phenergan^®. The information below is about brand name Phenergan. According to the FDA, “Generic medicines use the same active ingredients as brand-name medicines and work the same way, so they have the same risks and benefits as the brand-name medicines.”

Phenergan (promethazine) is a medication used to relieve allergy symptoms, nausea, and vomiting, as well as to help with sleep. It works by blocking histamine, a substance in the body that can cause symptoms like itching, sneezing, and runny nose. Phenergan may also be used to treat nausea caused by motion sickness or surgery. Common side effects include drowsiness, dry mouth, dizziness, and blurred vision. It’s important to avoid alcohol while taking Phenergan, as it can increase drowsiness, and it should not be used in children under 2 years old due to the risk of serious side effects.

Ondansetron is a medication used to prevent nausea and vomiting by blocking serotonin receptors in the brain and gut, which are involved in triggering the vomiting reflex. Its FDA-approved indications include the prevention of nausea and vomiting associated with chemotherapy, radiation therapy, and surgery. Off-label uses may include managing nausea in pregnancy (morning sickness) and gastroenteritis. Ondansetron is available in several forms, including oral tablets, orally disintegrating tablets, oral solution, and intravenous injections. Common side effects include headaches, constipation, and dizziness, while serious risks include a rare heart rhythm disorder (QT prolongation). Caution is advised in patients with heart conditions or those taking other medications that affect the QT interval.

Phenothiazine

5-HT3 receptor antagonist

Phenergan (promethazine) is used for:

• Perennial and seasonal allergic rhinitis

• Vasomotor rhinitis

• Allergic conjunctivitis due to inhalant allergens and foods

• Mild, uncomplicated allergic skin manifestations of urticaria and angioedema

• Amelioration of allergic reactions to blood or plasma

• Dermographism

• Anaphylactic reactions, as adjunctive therapy to epinephrine and other standard measures, after the acute manifestations have been controlled

• Preoperative, postoperative, or obstetric sedation

• Prevention and control of nausea and vomiting associated with certain types of anesthesia and surgery

• Therapy adjunctive to meperidine or other analgesics for control of post-operative pain

• Sedation in both children and adults, as well as relief of apprehension and production of light sleep from which the patient can be easily aroused

• Active and prophylactic treatment of motion sickness

• Antiemetic therapy in postoperative patients

Ondansetron is indicated for the prevention of:

• Nausea and vomiting associated with highly emetogenic cancer chemotherapy, including cisplatin greater than or equal to 50 mg/m²

• Nausea and vomiting associated with initial and repeat courses of moderately emetogenic cancer chemotherapy

• Nausea and vomiting associated with radiotherapy in patients receiving either total body irradiation, single high-dose fraction to the abdomen, or daily fractions to the abdomen

• Postoperative nausea and/or vomiting

• Typically taken orally up to four times daily depending on the specific purpose for use

• Comes in 12.5 mg, 25 mg, and 50 mg tablets

• Typically taken orally—see the full prescribing information for the recommended dosage in adults and pediatric

• Comes in 4 mg, 8 mg, and 24 mg tablets

Adverse reactions by system include:

• Central nervous system: Drowsiness is the most prominent CNS effect of this drug. Sedation, somnolence, blurred vision, dizziness, confusion, disorientation, and extrapyramidal symptoms such as oculogyric crisis, torticollis, and tongue protrusion, lassitude, tinnitus, incoordination, fatigue, euphoria, nervousness, diplopia, insomnia, tremors, convulsive seizures, excitation, catatonic-like states, hysteria. Hallucinations have also been reported

• Cardiovascular: Increased or decreased blood pressure, tachycardia, bradycardia, faintness

• Dermatologic: Dermatitis, photosensitivity, urticaria

• Hematologic: Leukopenia, thrombocytopenia, thrombocytopenic purpura, agranulocytosis

• Gastrointestinal: Dry mouth, nausea, vomiting, jaundice

• Respiratory: Asthma, nasal stuffiness, respiratory depression (potentially fatal) and apnea (potentially fatal)

• Other: Angioneurotic edema. Neuroleptic malignant syndrome (potentially fatal) has also been reported

• Paradoxical reactions

• Hyperexcitability and abnormal movements have been reported in patients following a single administration of Phenergan. Consideration should be given to the discontinuation of promethazine hydrochloride and to the use of other drugs if these reactions occur. Respiratory depression, nightmares, delirium, and agitated behavior have also been reported in some of these patients

The most common adverse reactions in adults for the:

Prevention of chemotherapy-induced (≥ 5%) are:

• Headache

• Malaise/Fatigue

• Constipation

• Diarrhea

Prevention of radiation-induced nausea and vomiting (≥ 2%) are:

• Headache

• Constipation

• Diarrhea

Prevention of postoperative nausea and vomiting (≥ 9%) are:

• Headache

• Low levels of oxygen

• Phenergan is contraindicated for use in pediatric patients less than two years of age

• Phenergan is contraindicated in comatose states, and in individuals known to be hypersensitive or to have had an idiosyncratic reaction to promethazine or to other phenothiazines

• Antihistamines are contraindicated for use in the treatment of lower respiratory tract symptoms including asthma

• Drug interactions: CNS depressants, epinephrine, anticholinergics, MAOIs

• Patients known to have hypersensitivity (e.g., anaphylaxis) to ondansetron or any components of the formulation

• Concomitant use of apomorphine

• Central nervous system depression

• Respiratory depression

• Lower seizure threshold

• Bone marrow depression

• Neuroleptic malignant syndrome

• Cholestatic jaundice

• Drugs having anticholinergic properties should be used with caution in patients with narrow-angle glaucoma, prostatic hypertrophy, stenosing peptic ulcer, pyloroduodenal obstruction, and bladder-neck obstruction

• Phenergan should be used cautiously in persons with cardiovascular disease or with impairment of liver function

• Phenergan may cause marked drowsiness or impair the mental and/or physical abilities required for the performance of potentially hazardous tasks, such as driving a vehicle or operating machinery. The use of alcohol or other central-nervous-system depressants such as sedatives/hypnotics (including barbiturates), narcotics, narcotic analgesics, general anesthetics, tricyclic antidepressants, and tranquilizers, may enhance impairment

• Patients should be advised to report any involuntary muscle movements

• Avoid prolonged exposure to the sun

• Pregnancy: Phenergan should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus

• Breastfeeding: Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from Phenergan a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother

• Hypersensitivity reactions, including anaphylaxis and bronchospasm

• QT interval prolongation and Torsade de pointes

• Serotonin syndrome

• Myocardial ischemia

• Masking of progressive ileus and/or gastric distension following abdominal surgery or chemotherapy-induced nausea and vomiting

WARNING

Phenergan should not be used in pediatric patients less than 2 years of age because of the potential for fatal respiratory depression.

Postmarketing cases of respiratory depression, including fatalities, have been reported with use of Phenergan in pediatric patients less than 2 years of age. A wide range of weight-based doses of Phenergan have resulted in respiratory depression in these patients.

Caution should be exercised when administering Phenergan to pediatric patients 2 years of age and older. It is recommended that the lowest effective dose of promethazine hydrochloride be used in pediatric patients 2 years of age and older and concomitant administration of other drugs with respiratory depressant effects be avoided.

*This information is from the label for brand name Phenergan^®. See the Full Prescribing Information for more complete information. Promethazine, the active ingredient in Phenergan, may also be the active ingredient in other medications, and this information may not be accurate for all medications that include the active ingredient promethazine.

*This information is from the ondansetron hydrochloride label used by Aurobindo Pharma Limited. See the Full Prescribing Information for more complete information. This information may not be accurate for all medications that include the active ingredient ondansetron.