Lamivudine belongs to a group of medications known as antivirals. It is used to treat people with chronic hepatitis B infection and evidence of hepatitis B virus replication (reproduction). It works by stopping the hepatitis B virus from reproducing. There is no cure for hepatitis B infection; lamivudine can decrease the amount of hepatitis B virus in the body and may reduce the damage done to the liver by the hepatitis B virus.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose for adults and adolescents 16 years of age and older is 100 mg (one tablet or 20 mL oral solution) once daily. People with reduced kidney function may require a lower dose, as directed by their doctor.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

Lamivudine can be taken with or without food. The tablet should be swallowed whole with water. If you are taking the oral solution, use a measuring device (e.g., an oral syringe or a measuring spoon) that is marked for accurate dosing.

Do not stop taking this medication without telling your doctor. Your hepatitis may get worse if you stop this medication.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature and keep it out of the reach of children.

Oral Solution

Each mL of oral solution, colourless-to-pale-yellow, strawberry-banana flavoured, clear liquid, contains 5 mg of lamivudine. Nonmedicinal ingredients: artificial strawberry and banana flavours, citric acid (anhydrous), methylparaben, propylene glycol, propylparaben, sodium citrate, and sucrose.

Tablet

Each butterscotch-coloured, film-coated, capsule-shaped tablet, engraved "GXCG5" on one side, contains 100 mg of lamivudine. Nonmedicinal ingredients: hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polyethylene glycol 400, polysorbate 80, sodium starch glycolate, synthetic red iron oxide, synthetic yellow iron oxide, and titanium dioxide.

Do not use this medication if you are allergic to lamivudine or any ingredients of the medication.

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• abdominal or stomach pain and discomfort
• cough
• diarrhea
• dizziness
• fatigue
• hair loss
• headache
• muscle pain
• nausea
• rash
• trouble sleeping
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• severe muscle pain or cramping
• signs of anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
• signs of high lactic acid levels in the blood (e.g., nausea, vomiting, increased breathing rate, abdominal pain, unusual tiredness, dizziness, rapid heart rate)
• signs of infection (fever, severe chills, sore throat, mouth ulcers)
• signs of muscle damage (e.g., muscle pain, tenderness or weakness, or brown or discoloured urine) - especially if you also have a fever or a general feeling of being unwell
• signs of poor blood clotting (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• symptoms of ear, nose, or throat infection, such as fever, chills, cough, or sore throat
• tingling; burning; numbness; or pain in the hands, arms, feet, or legs

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., difficulty breathing, hives, swelling of the face, lips, eyes, or throat)
• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, chills, fever, nausea, rapid heartbeat, swollen abdomen)
• symptoms of lactic acidosis (e.g., abdominal pain, diarrhea, fatigue, nausea, shortness of breath, vomiting, weakness, weight loss)
• symptoms of liver problems (e.g., nausea, vomiting, abdominal pain, weakness, diarrhea)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Diabetes: An adult dose of the oral solution of lamivudine 100 mg (20 mL) contains 4 g of sucrose. This may affect your control of blood glucose levels if you have diabetes.

Hepatitis B transmission: Treatment with lamivudine has not been proven to reduce the risk of passing on hepatitis B to other people through sexual contact and blood transfer. You should continue to take measures to prevent giving hepatitis B to other people (e.g., using condoms) while taking this medication.

Human immunodeficiency virus (HIV): Treatment of hepatitis B with lamivudine requires lower doses than treatment for HIV infection. If you are taking lamivudine for hepatitis B and later learn that you have HIV, tell your doctor immediately as the lower dose of lamivudine used for treating hepatitis B is not effective against HIV infection.

Kidney function: Kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. People with reduced kidney function may need a lower dose of the medication. If you have kidney disease or decreased kidney function, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Lactic acidosis and enlarged liver: Lamivudine can cause a rare but serious condition called lactic acidosis (buildup of lactic acid in the blood) together with an enlarged liver. This tends to occur more often in women, especially if they are overweight. If you experience any of the following symptoms, call your doctor immediately:

• abdominal pain, swelling, or bloating
• diarrhea
• fatigue
• feeling unwell
• nausea
• shortness of breath
• vomiting
• weakness
• weight loss

Your doctor will monitor your liver function periodically by ordering laboratory tests.

Pancreatitis (inflammation of the pancreas): Lamivudine may cause or worsen pancreatitis. Although this is more likely to happen with children taking a higher dose as required to treat HIV, if you have a history of or are at risk for developing pancreatitis, you should be closely monitored by your doctor while taking this medication. If you develop signs of pancreatitis (e.g., upper left abdominal pain, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen), contact your doctor.

Stopping the medication: If you stop taking this medication, your hepatitis B infection could get worse. Take the medication exactly as prescribed by your doctor, and do not stop taking the medication without checking with your doctor first.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: Lamivudine passes into breast milk. If you are breast-feeding and are taking this medication, it may affect your baby. Breast-feeding is not recommended for women taking this medication.

Children: The safety and effectiveness of using this medication have not been established for children under 16 years of age or those who are also infected with Delta hepatitis.

Seniors: People over the age of 65 years may require lower doses of this medication due to age-related decreases in kidney function.

There may be an interaction between lamivudine and any of the following:

• alpha interferon
• cladribine
• co-trimoxazole (sulfamethoxazole/trimethoprim)
• emtricitabine
• orlistat
• trimethoprim
• zidovudine

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.