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Zeffix (lamivudine; antiviral)

Written by Stephanie Nera, RPh, PharmD · Pharmacology

Updated May 28, 2021

Zeffix is the brand name of the drug lamivudine. Lamivudine is an antiviral agent for treating hepatitis B and HIV infections. It works by inserting itself into the DNA strand of the virus. This results in chain termination and stops viral replication.



What is Zeffix used for?

Zeffix is commonly used to treat patients with long-term (chronic) viral infection of the liver caused by hepatitis B. However, it has not been shown to reduce the risk of passing hepatitis B to others.

Zeffix may be prescribed for other uses; ask your doctor or pharmacist for more information.

How should I take Zeffix?

As an oral tablet, it should be swallowed whole with a glass of water. It can be taken with or without food. The medication should be taken regularly to be effective.

How do I store Zeffix?

This product is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store it in the bathroom or the freezer. There may be different brands of lamivudine that may have different storage needs.

That is why it is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush this product down the toilet or pour them into a drain unless instructed to do so. Additionally, it is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using Zeffix?

Consult with your doctor or pharmacist, if you are/have:

  • Pregnant or breastfeeding.
  • Taking any other medicines. This includes both prescription and over-the-counter (OTC) medications, such as herbal remedies and dietary supplements.
  • Allergy with any of active or inactive ingredients of Zeffix or other medications.
  • Any other types of allergies, such as to foods, dyes, preservatives, or animals.
  • Any other illnesses, disorders, or medical conditions, such as liver problems or kidney problems.
  • Is it safe during pregnancy or breastfeeding?

    There are no adequate studies in women for determining risk when using this medication during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking this medication. This medication is pregnancy risk category C, according to the US Food and Drug Administration (FDA).

    FDA pregnancy risk category reference below:

    • A=No risk
    • B=No risk in some studies
    • C=There may be some risk
    • D=Positive evidence of risk
    • X=Contraindicated
    • N=Unknown

    Side effects

    What side effects can occur from Zeffix?

    Here are common side effects:

    • Headache
    • Vomiting
    • Diarrhea
    • Nausea
    • Fatigue/tiredness
    • Abdominal discomfort and pain
    • Coughing, with phlegm, not associated with a cold or flu
    • Dizziness
    • Abnormal liver function tests
    • Muscle disorders (including muscle pain and cramps)

    Tell your doctor immediately if you notice any of the following:

    • Wheezing
    • Swelling of the lips/mouth
    • Difficulty in breathing
    • Hay fever
    • Hives
    • Fainting
    • Not everyone experiences these side effects. In addition, there may be other side effects not listed above. If you have any concerns about a side effect, please consult your doctor or pharmacist.


      What drugs may interact with Zeffix?

      Zeffix may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects.

      To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs, and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

      Here are some medications may interact with Zeffix, such as:

      • Trimethoprim
      • Zidovudine
      • Abacavir
      • Didanosine
      • Zalcitabine
      • Emtricitabine

      Does food or alcohol interact with Zeffix® (Lamivudine)?

      Zeffix may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

      What health conditions may interact with Zeffix?

      Zeffix may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have, especially:

      • Kidney problems
      • Problems with your pancreas


      The information provided is not a substitute for any medical advice. Therefore, you should always consult with your doctor or pharmacist before using this medication.

      What is the dose for an adult?

      For HIV co-infection

      Take 150 mg twice a day, in combination with other antiretroviral therapy drugs.

      For chronic hepatitis B infection

      Take 100 mg once a day. Your doctor may prescribe a higher or lower dose.

      What is the dose for a child?

      The safety and efficacy of Zeffix has not been established in children below 18 years old. Consult with your child’s pediatrician regarding the proper dose of this medication.

      How is Zeffix available?

      Zeffix is available in the following dosage forms and strengths:

      • Film-coated tablet 100 mg

      What should I do in case of an emergency or overdose?

      In case of an emergency or an overdose, call your local emergency services or go to the nearest emergency room.

      What should I do if I miss a dose?

      If you miss a dose, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.


      Hello Health Group does not provide medical advice, diagnosis or treatment.

      Written by

      Stephanie Nera, RPh, PharmD


      Updated May 28, 2021

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