Zidovudine

Zidovudine is approved for two main uses across its supported products:

• Treatment of HIV-1 infection: Retrovir capsules, oral solution, and injection — as well as Zidovudine capsules, tablets, and oral solution — are all indicated for treating HIV-1 infection in adults and children. It must always be used together with other antiretroviral medicines.
• Prevention of mother-to-baby HIV-1 transmission: Retrovir capsules, oral solution, and injection, and Zidovudine capsules, tablets, and oral solution are approved to reduce the risk of passing HIV-1 from a pregnant mother to her baby. The regimen involves treating the mother before labor (antepartum), during labor (intrapartum), and treating the newborn after birth (postpartum). In most cases, additional antiretroviral medicines are used alongside zidovudine for this purpose. This approval is based on use after 14 weeks of pregnancy.

Zidovudine belongs to a class of antiretrovirals called nucleoside reverse transcriptase inhibitors (NRTIs). HIV needs an enzyme called reverse transcriptase to copy its genetic material and multiply inside your cells. Zidovudine works by blocking this enzyme, which prevents HIV from replicating and helps keep viral levels in the body under control. It does not cure HIV but is an important part of combination therapy that manages the infection.

Zidovudine is taken orally (as capsules, tablets, or oral solution) twice a day in most adults, with or without food. Retrovir injection is given intravenously over one hour in a hospital or clinical setting and is intended only as a temporary measure until oral dosing is possible. Pediatric doses are always calculated by a healthcare provider based on the child's body weight and must not exceed the adult dose — children who cannot swallow tablets or capsules should use the oral solution form.

• Can be taken with or without food
• Oral forms are generally taken twice daily in adults
• Children's doses are weight-based — always follow your prescriber's instructions
• If you miss a dose, follow your prescriber's guidance; do not double up without advice

The most common side effects reported in adult trials include headache, nausea, general malaise (feeling unwell), loss of appetite, and vomiting. In pediatric trials, fever and cough were reported most often.

• Headache
• Nausea
• Malaise (general feeling of being unwell)
• Loss of appetite
• Vomiting
• Muscle aches, myalgia (muscle pain), or joint pain
• Insomnia
• Fatigue

More serious reactions — including severe anemia, low white blood cell counts (neutropenia), muscle damage (myopathy), and signs of lactic acidosis or liver problems — require immediate medical attention. Contact your doctor right away if you notice unusual tiredness, paleness, muscle weakness, stomach pain, or difficulty breathing.

• Blood toxicity (anemia and neutropenia): Zidovudine can seriously lower red and white blood cell counts. This risk is highest in people with advanced HIV or already-low blood counts. Regular blood tests are strongly recommended, and dosing may need to be paused or reduced.
• Muscle damage (myopathy): Long-term use has been linked to muscle pain, weakness, and inflammation similar to HIV-related muscle disease. Tell your doctor about any new or worsening muscle symptoms.
• Lactic acidosis and liver enlargement: Rare but potentially fatal. Women and people with obesity appear to be at higher risk. Stop the medicine and seek care immediately if you experience rapid breathing, unexplained fatigue, nausea, stomach pain, or vomiting.
• Lipoatrophy (fat loss): Treatment can cause loss of fat under the skin, especially in the face, limbs, and buttocks. This may be only partially reversible after stopping the medicine. Your doctor should check for this regularly.
• Ribavirin and interferon use in HIV/hepatitis C co-infection: Combining zidovudine with ribavirin is not advised because it can worsen anemia. Use with interferon alfa (with or without ribavirin) has caused serious liver problems and worsening blood counts in co-infected patients.
• Immune reconstitution syndrome: As your immune system recovers on antiretroviral therapy, it may react to previously hidden infections (such as tuberculosis or certain fungal infections). Autoimmune conditions have also been reported. Tell your doctor if you develop new or worsening symptoms after starting treatment.

Zidovudine can interact with several other medicines in ways that increase risk of side effects or reduce effectiveness:

• Stavudine: Must not be used together — these two antiretrovirals counteract each other.
• Ribavirin: Reduces zidovudine's ability to fight HIV and significantly worsens anemia; avoid combining.
• Doxorubicin (chemotherapy): Shown to interfere with zidovudine in lab studies; avoid concurrent use.
• Ganciclovir, interferon alfa, and other bone marrow–suppressive or cytotoxic agents: These can add to zidovudine's blood-cell toxicity, increasing the risk of severe anemia and low white blood cell counts.

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Allergy: Do not take zidovudine if you have ever had a life-threatening allergic reaction (such as anaphylaxis or Stevens-Johnson syndrome) to zidovudine or any component of the formulation.
• Kidney disease or dialysis: Dose adjustment is needed if kidney function is severely reduced or if you are on hemodialysis or peritoneal dialysis.
• Liver disease: Zidovudine is processed by the liver, so levels build up more in people with liver problems. More frequent blood monitoring is recommended; there are insufficient data to recommend a standard dose adjustment for liver cirrhosis.
• Low blood counts: Use with caution if you already have low red or white blood cell counts; zidovudine can worsen these significantly.
• Pregnancy: Zidovudine crosses the placenta. It is approved to prevent mother-to-baby HIV transmission, but use in the first trimester should be carefully considered with your doctor. Register with the Antiretroviral Pregnancy Registry if you take this medicine during pregnancy.
• Breastfeeding: Do not breastfeed while taking zidovudine. HIV can be passed through breast milk, and zidovudine is present in human milk.
• Children: Zidovudine has been studied in HIV-1-infected children as young as 6 weeks and in newborns exposed to HIV around birth. Doses must be calculated by a healthcare provider based on body weight.
• Older adults: Dose selection should be cautious because older patients are more likely to have reduced kidney, liver, or heart function or to be taking other medications.

Overdose with zidovudine has been reported in both adults and children. There are no unique symptoms beyond those that can occur as regular side effects — such as fatigue, headache, vomiting, and possible blood count changes. People who have overdosed have generally recovered without permanent harm. If an overdose is suspected, the patient should be monitored for toxicity and given supportive care; dialysis has little effect on removing zidovudine itself, though it does help clear its main breakdown product.

When taken by mouth, zidovudine is absorbed quickly, with blood levels peaking within about 30 minutes to 1.5 hours. It can be taken with or without food without meaningfully affecting how much the body absorbs. The drug is widely distributed in the body — including into the fluid around the brain and spinal cord (cerebrospinal fluid), which is relevant in HIV treatment — and is processed mainly by the liver. It is then eliminated primarily through the urine, with a half-life (the time for half the drug to leave the body) of roughly 0.5 to 3 hours. In people with severe kidney disease or those on dialysis, zidovudine and its breakdown products clear more slowly, which is why dose adjustments may be needed.

Store at 15° to 25°C (59° to 77°F) and protect from moisture. Store at 15° to 25°C (59° to 77°F). Store vials at 15° to 25°C (59° to 77°F) and protect from light.