Lamivudine and Zidovudine

Lamivudine and zidovudine is a two-drug combination antiviral used as part of a complete HIV-1 treatment regimen.

• Combivir (oral tablet) is indicated in combination with other antiretrovirals for the treatment of HIV-1 infection in adults and adolescents weighing at least 30 kg
• Combivir is also indicated for pediatric patients weighing at least 30 kg who can reliably swallow tablets
• Lamivudine and Zidovudine tablets (generic) are indicated in combination with other antiretrovirals for the treatment of HIV-1 infection in adults, adolescents, and eligible pediatric patients
• Neither product is intended to be used alone — both must be part of a combination antiretroviral regimen

Both lamivudine and zidovudine belong to a class of drugs called nucleoside analogue reverse transcriptase inhibitors (NRTIs). HIV needs an enzyme called reverse transcriptase to copy its genetic material inside your cells — a step required for the virus to replicate. These two drugs mimic the building blocks the virus tries to use, but when incorporated, they act like a dead end, stopping the copying process. With replication blocked, the amount of HIV in the body is kept lower, helping preserve immune function.

Because HIV can develop resistance to antiretroviral drugs over time, these tablets are always used alongside other antiretroviral agents — each targeting the virus in a slightly different way — to make it harder for the virus to escape treatment.

Lamivudine and zidovudine tablets are taken by mouth twice daily. The tablets can be taken with or without food. Because this is a fixed-dose combination, the dose cannot be adjusted — so it is not suitable for everyone (see warnings below).

• Adults, adolescents, and children weighing at least 30 kg: one tablet twice daily
• Children who cannot reliably swallow the tablet should use separate liquid formulations of lamivudine and zidovudine instead
• Always follow your prescriber's instructions; do not stop or change your dose without talking to your doctor first

The most commonly reported side effects (in 15% or more of patients in clinical studies) include:

More serious reactions — including severe anemia, dangerously low white blood cell counts, muscle damage, lactic acidosis, and liver problems — have also been reported and require prompt medical attention. See the Boxed Warning section for details on what symptoms to watch for.

• Lactic acidosis and liver damage: A potentially fatal buildup of acid in the blood, sometimes with severe liver swelling and fat accumulation, has been reported. Stop this medication and seek emergency care if you have stomach pain, nausea, vomiting, unusual weakness, trouble breathing, or feel very cold or dizzy.
• Blood toxicity: Zidovudine can cause severe drops in red and white blood cell counts. Regular blood monitoring is essential, especially in people with advanced HIV.
• Muscle damage (myopathy): Long-term zidovudine use has been associated with painful muscle damage. Report any new or worsening muscle pain or weakness.
• Hepatitis B flare on stopping: In patients co-infected with HIV and hepatitis B, stopping this medication can trigger a severe and potentially fatal hepatitis B flare. Liver function must be monitored closely for several months after stopping.
• Fixed-dose — cannot be adjusted: Because the dose can't be changed, this tablet is not appropriate for patients with significant kidney impairment (creatinine clearance below 50 mL/min), liver impairment, or those who need a lower dose due to side effects.
• Do not double up: Do not take this alongside other products containing lamivudine, zidovudine, or emtricitabine.
• Immune reconstitution syndrome: When HIV treatment starts working, the recovering immune system can react to previously hidden infections or trigger autoimmune conditions — sometimes requiring additional treatment.

Several medications interact significantly with lamivudine and zidovudine — some combinations should be completely avoided:

• Stavudine: Antagonizes (works against) zidovudine — avoid combining
• Zalcitabine: Can block lamivudine from working properly — avoid combining
• Doxorubicin (chemotherapy): Reduces zidovudine's antiviral activity — avoid combining
• Ribavirin: Can reduce how well both lamivudine and zidovudine work, and combining ribavirin with zidovudine can worsen anemia — co-administration is not advised
• Interferon alfa (with or without ribavirin): In patients co-infected with HIV and hepatitis C, this combination has led to serious — sometimes fatal — liver failure, as well as worsening anemia and low white blood cell counts
• Ganciclovir, interferon alfa, and other bone marrow–suppressing drugs: Can amplify zidovudine's blood toxicity
• Other lamivudine-, zidovudine-, or emtricitabine-containing products: Taking these alongside this tablet creates dangerous duplicate dosing — always check with your pharmacist

Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.

• Tell your doctor if you have ever had a severe allergic reaction (anaphylaxis or Stevens-Johnson syndrome) to lamivudine or zidovudine — this medication is contraindicated in those cases
• Tell your doctor if you have kidney disease — this fixed-dose tablet is not appropriate if your kidney function is significantly reduced
• Tell your doctor if you have liver disease or hepatitis B — your liver will need ongoing monitoring, and stopping this drug can trigger a dangerous hepatitis B flare
• Tell your doctor if you have low blood counts or bone marrow problems — regular monitoring will be needed
• Tell your doctor if you have a history of pancreatitis (inflamed pancreas), especially for pediatric patients
• If you are pregnant, discuss the risks and benefits with your doctor — both drugs have been studied in pregnancy, and a registry (Antiretroviral Pregnancy Registry) exists to track outcomes
• Do not breastfeed if you have HIV — the CDC recommends against it due to the risk of transmitting HIV to your infant
• Children must weigh at least 30 kg and be capable of swallowing tablets to use this product; smaller children or those who cannot swallow tablets need the separate liquid formulations

There is no known antidote for an overdose of lamivudine and zidovudine tablets. If an overdose is suspected, contact Poison Control (1-800-222-1222) or go to an emergency room immediately. In reported zidovudine overdose cases, the most common symptoms were nausea and vomiting, though headache, dizziness, drowsiness, confusion, and in rare cases seizures were also noted — all patients in those reports recovered.

Both lamivudine and zidovudine are well absorbed when taken by mouth. Lamivudine has an oral bioavailability of about 86%, while zidovudine's is about 64%. Both distribute widely throughout the body and bind only minimally to plasma proteins. Lamivudine is mostly excreted unchanged through the kidneys, with very little liver metabolism. Zidovudine, on the other hand, is primarily broken down by the liver into an inactive metabolite (GZDV), with a smaller amount converted to another metabolite (AMT). Neither drug is significantly processed by the cytochrome P450 enzyme system, which reduces the risk of many common drug interactions.

Store at 20º to 25ºC (68º to 77ºF); excursions permitted to 15º to 30ºC (59º to 86ºF) Preserve in well-closed containers, protected from light.