How does Zeffix work?

Zeffix tablets contain the active ingredient lamivudine, which is a type of medicine called a nucleoside reverse transcriptase inhibitor. It is used in the treatment of hepatitis B infection. Lamivudine tablets are also available without a brand name, ie as the generic medicine. (Lamivudine is also used to treat HIV infection, but when used for this purpose, higher doses than those found in Zeffix are needed. See the Epivir factsheet for more information on this use of lamivudine.)

Hepatitis B is a virus that infects the liver and leads to liver damage. Once the virus is inside the liver cells it multiplies. Part of this process involves the virus making copies of its genetic material (DNA). This is achieved by a compound essential to the virus, called viral DNA polymerase. Viral DNA polymerase is a compound known as an enzyme. Lamivudine works by blocking the action of this enzyme. This stops the virus from multiplying.

Lamivudine lowers the amount of hepatitis B virus in the body. This leads to a reduction in liver damage and an improvement in liver function.

How do I take Zeffix?

Always follow the instructions given by your doctor.

The usual dose of Zeffix for adults is one 100mg tablet taken once a day. Take your tablet at the same time each day.

The tablets can be taken either with or without food.

If you forgot to take a dose at your usual time you should take it as soon as you remember and then take your next dose at your usual time. Do not take a double dose to make up for a missed dose.

You should keep taking this medicine regularly every day until your doctor tells you to stop.


Important information about Zeffix

Your liver function and the amount of hepatitis B virus in your body should be regularly monitored while you are taking this medicine. This will involve having blood tests before, during and after treatment with this medicine.

You should not stop taking this medicine unless instructed to by your doctor, as this may cause your hepatitis to get worse. If your doctor tells you to stop treatment your liver function will need to be monitored for at least a further four months to check for any problems.

This medicine helps to control your hepatitis B infection, but it is not known if it will cure it. This means that you could still be at risk of transmitting the virus to other people through sexual contact or blood contamination. You should continue to use condoms to prevent transmitting the virus to your sexual partner. There is a vaccine against hepatitis B available to protect people who may be at risk of catching the virus.

The class of medicines that lamivudine belongs to can cause a rare but serious condition called lactic acidosis, which is an excess of lactic acid in the blood, together with an enlarged liver. This side effect is more likely to occur in overweight women and people with other liver disease (particularly hepatitis C treated with alpha interferon and ribavirin). If it occurs, lactic acidosis usually develops after a few months of treatment. Your doctor will monitor you for this side effect, but symptoms that might indicate it’s development include rapid and/or deep breathing and non-specific symptoms such as feeling weak, sick or generally unwell, vomiting, abdominal pain, loss of appetite or weight loss. You should tell your doctor if you experience any of these.

Zeffix is not licensed for children and adolescents under 18 years of age. However it may be prescribed by specialists for children aged two years and over. For more information talk to your doctor or pharmacist.


Zeffix should be used with caution by

  • People with decreased kidney function (a lower dose may be needed).
  • People with HIV infection.
  • People also infected with hepatitis C.
  • People with an enlarged liver (hepatomegaly).
  • People with a history of alcohol abuse.
  • Obese women.

Zeffix should not be used by

This medicine should not be used if you are allergic to any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

The safety of this medicine in pregnancy has not been established. It should only be used during pregnancy if the expected benefit to the mother outweighs any potential risk to the developing foetus. It is not recommended in the first trimester. Seek medical advice from your doctor.

This medicine passes into breast milk, as does the hepatitis B virus. It is recommended that mothers who need to take this medicine do not breast feed their infants. Seek medical advice from your doctor.


Possible side effects of Zeffix

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Just because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

Very common (affect more than 1 in 10 people)

  • Elevation of liver enzymes such as alanine aminotransferase (ALT).

Common (affect between 1 in 10 and 1 in 100 people)

  • Elevated levels of creatinine phosphokinase (CPK) in your blood.
  • Muscle pain and cramps.
  • Skin rash and itching.

Rare (affect between 1 in 1000 and 1 in 10,000 people)

Swelling of the lips, throat and tongue (angioedema).

Frequency not known

Decreased numbers of blood cells called platelets in the blood (thrombocytopenia).

Muscle breakdown (rhabdomyolysis).

The side effects listed above may not include all of the side effects reported by the medicine’s manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can lamivudine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to make sure that the combination is safe.

Trimethoprim may increase the blood level of lamivudine, which could increase the risk of its side effects. This should not require a dose adjustment unless you have kidney problems. However you may need extra monitoring by your doctor if you are prescribed trimethoprim or co-trimoxazole (which contains trimethoprim) while taking this medicine. The manufacturer recommends that high doses of co-trimoxazole for the treatment of Pneumocystis carinii pneumonia (PCP) and toxoplasmosis should be avoided in people taking lamivudine.

The manufacturer recommends that lamivudine is not used in combination with the following medicines:

  • cladribine
  • emtricitabine
  • other medicines containing lamivudine.
  • Other medicines containing lamivudine
  • Lamivudine tablets are also available without a brand name, ie as the generic medicine.
  • Epivir contains a higher dose of lamivudine than Zeffix and is used to treat HIV infection, not hepatitis B.

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