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Treatment Name: Promethazine (Phenergan®)

Promethazine (Phenergan®) is a Supportive Care Therapy to prevent or treat Nausea and Vomiting

How does promethazine (Phenergan®) work?
Promethazine is designed to block receptors in your brain that can cause nausea and vomiting called histamine (H1) receptors.

When chemotherapy is given, it can cause histamine to be released. When histamine binds to H1 receptors in the brain, this can contribute to the body's reflex to induce vomiting. Promethazine binds to H1 receptors instead of histamine, and thereby decreases the reflex to vomit.

Goals of therapy:
Promethazine (Phenergan®) is usually taken on an as needed basis to treat nausea and vomiting. When certain triggers of vomiting are known, such as motion sickness, promethazine may be taken 30 - 60 minutes before these triggers to prevent nausea and vomiting.


Promethazine (Phenergan®) is usually taken at home or given in the hospital to treat breakthrough nausea and vomiting. Promethazine may also be useful to prevent or treat motion sickness. Promethazine is available in 12.5 mg, 25 mg, or 50 mg tablet strengths. Promethazine (Phenergan®) is also available as liquid syrup.

  • Usual promethazine (Phenergan®) starting dose:
    • Promethazine 12.5 to 25 mg oral tablet by mouth every 4 to 6 hours as needed
    • Promethazine 6.25 to 25 mg intravenous push (I.V. Push) every 4 to 6 hours as needed
    • Promethazine 25 mg rectal suppository every 6 hours as needed (do NOT use suppositories while neutropenic due to the risk of neutropenic fever)

Patients age 65 years or older should use the lowest dose that takes prevents or treats nausea in order to avoid excessive sleepiness and sedation.

Promethazine is typically taken on an as needed basis during chemotherapy treatment. It begins to work roughly 20 minutes after it is taken and lasts for 4 to 6 hours. Overall duration of therapy depends upon number of cycles chemotherapy prescribed. It can often be discontinued within a few days after the last dose of chemotherapy when it is no longer needed.

Side Effects

In the prescribing label information (promethazine (Phenergan®) package insert), the most commonly reported side effects from promethazine (Phenergan®) are shown here. The exact percentages of patients that will experience promethazine side effects is unknown because it has been used under widely varying patient populations in a variety of clinical trials:

  • Drowsiness (most common)
  • Blurred vision
  • Dizziness
  • Confusion
  • Dry mouth
  • Uncontrolled shaking or muscle tremors
  • Ringing in the ears
  • Fatigue
  • Double vision
  • Seizures
  • Increased or decreased blood pressure
  • Increased or decreased heart rate
  • Low platelets (rare)
  • Low white blood cells (rare)
  • Decreased breathing rate*
  • Irritation to blood vessels (with I.V. administration)

Promethazine should be used in pregnant women only if the potential benefits to the mother outweigh the potential risks to the unborn baby.

*Caution should be used when using promethazine in patients with COPD (chronic obstructive pulmonary disorder), sleep apnea, or those with other breathing problems.

Side effect videos Side Effect Videos
Nausea and VomitingNausea and VomitingFatigue Fatigue


How often is monitoring needed?
Labs (blood tests) typically do not need to be monitored for promethazine, but may be checked before each chemotherapy treatment. These include a comprehensive metabolic panel (CMP) to check liver function

How often is imaging needed?
An electrocardiogram (“ECG” or “EKG”) is usually not necessary, but may be done to check your heart rhythm as promethazine can prolong the QTc interval leading to a heart arrhythmia, especially if you are on other medications that can also prolong the QTc interval or taking high doses of promethazine.

How might blood test results/imaging affect treatment?
Depending upon the results, your doctor may advise to continue promethazine as planned, reduce the dose of future treatments, or switch to an alternative therapy. The use of promethazine has been associated with jaundice (an increase in serum bilirubin, as measured using a CMP) Promethazine (Phenergan®) has been reported to interfere with certain pregnancy tests in women. Both false positives and false negatives have been reported. Ask your doctor or pharmacist for more information on the effect of promethazine on pregnancy tests.

ChemoExperts Tips

  • When given intravenously, promethazine can potentially cause irritation and damage to the blood vessels and surrounding tissues. Notify your doctor or nurse immediately if you feel discomfort during the infusion. If you have a central line (port), the risk of this adverse reaction is much lower
  • Drowsiness is a very common side effect of promethazine (Phenergan®) and may increase your risk of falling down and getting injured. The use of alcohol with promethazine may further increase this risk. Do not drive or operate machinery after taking a dose of promethazine until you know how your body reacts to the medication. Instead, ask your doctor or pharmacist about taking other non-drowsy anti-nausea medications such as ondansetron (Zofran®) if you plan on being active and do not want to be tired
  • You may take promethazine at the first sign of nausea. It is important not to wait until the nausea gets too severe to take your dose as it takes approximately 30 minutes for the drug to work and if vomiting occurs before then, you may end up vomiting up your dose of promethazine
  • Promethazine should be used with caution in those with a seizure history or at high risk for seizures as it may lower the seizure threshold
  • Do not take promethazine more frequently than prescribed as this increases the risk of experiencing side effects. You may use other anti-nausea medications such as ondansetron if you are still experiencing nausea after taking promethazine
  • When opioid pain medications are used with promethazine, the dose of pain medication may need to be reduced to avoid excessive sedation and symptoms of restlessness
  • Do not use rectal suppositories if you have a very low white blood cells (neutropenic) as this may increase your risk of developing neutropenic fever
  • There are no well-controlled studies with promethazine (Phenergan®) use in pregnant women. Ask your doctor or pharmacist before using while pregnant. Promethazine should only be used during pregnancy if the benefit potential outweighs the potential risks to the unborn baby
  • A pharmacist should ALWAYS review your medication list to ensure that drug interactions are prevented or managed appropriately
  • Store promethazine (Phenergan®) at room temperature (68°-77°F)

Patient Assistance & Co-payment Coverage

Patients under the age of 65 years, or those with private insurance plans:
If you have insurance and are looking for patient assistance or copay assistance for Promethazine (Phenergan®), we have provided links that may help.

Visit our Patient Assistance page and click the links to various patient assistance programs for help paying for Promethazine (Phenergan®). Depending upon your income, they may be able to help cover the cost of:

  • Promethazine (Phenergan®)

For Branded medications (may be available for generic medications too), check with the manufacturer to determine if a co-pay card is offered and if it could reduce your monthly copay.

  • If you are uninsured, check with the manufacturer to determine if you are eligible to receive medication at no cost.

Medicare and Medicaid patients (Patients 65 years or older):
The clinic providing treatment will likely pre-authorize medications and immune therapies such as Promethazine (Phenergan®) and are the best source to help you understand drug cost.

  • Ask to speak with a patient assistance technician or financial counselor at the clinic or hospital administering this therapy.

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Promethazine prescribing label information. Phenergan package insert.

Created: January 7, 2018 Updated: January 7, 2018

What is Nausea and Vomiting?

Nausea is the sensation that there is a need to vomit. Nausea can be acute and short-lived, or it can be prolonged. When prolonged, it is a debilitating symptom. Nausea (and vomiting) can be psychological or physical in origin.

NOTE: Treatment Options listed below are not all-inclusive. Other treatments may be available. ChemoExperts provides drug information and does not recommend any one treatment over another. Only your Doctor can choose which therapy is appropriate for you.

What is a CMP?

A Comprehensive Metabolic Panel (CMP) is a frequently ordered blood test that tells clinicians the status of your: 1) Electrolytes & Acid/Base status2) Kidney function, 3) Liver function, 4) Blood sugar, and 5) Calcium at the time the test was taken. It is commonly used to monitor liver and kidney function when beginning new medications such as chemotherapy. A total of 14 tests are run simultaneously and are shown below.

Electrolytes & Acid/Base status:
1) Sodium, 2) Potassium, 3) Carbon dioxide, 4) Chloride

Kidney Function:
5) BUN (blood urea nitrogen), 6) Serum creatinine (Scr)

Liver Function:
7) AST, 8) ALT, 9) Total bilirubin, 10) Alk Phos, 11) Albumin, 12) Total protein

Blood sugar:
13) Serum glucose

14) Serum calcium

What is the QTc interval?

The time it takes your heart to make one beat can be measured using an electrocardiogram (ECG, or EKG) and is reported as the QTc interval. Promethazine is generally safe to give when the QTc interval for men is less than 450 milliseconds per beat, and for women, less than 460 milliseconds per beat.

The QTc interval is prolonged if the heart takes too long to make the next beat, and could lead to a dangerous heartbeat known as an arrhythmia.

Certain medications, in addition to promethazine, may prolong the QTc interval. The list includes: ondansetron (Zofran®), levofloxacin or ciprofloxacin antibiotics. Make sure your pharmacist checks all new medications to make sure they do not prolong the QTc interval.