Zidovudine belongs to the class of antiretroviral medications called nucleoside reverse transcriptase inhibitors (NRTIs). It is used in combination with other medications to treat the infection caused by the human immunodeficiency virus (HIV). Zidovudine is also used to help prevent pregnant women who have HIV infection from passing the virus to their child during birth.

HIV is the virus responsible for acquired immune deficiency syndrome (AIDS). HIV infection destroys CD4 (T) cells, which are important to the immune system. The immune system helps fight infections.

Reverse transcriptase is a part of HIV required to infect cells and make more virus. Zidovudine prevents reverse transcriptase from working properly.

Zidovudine does not cure AIDS and does not prevent it from being spread to others. It does help to slow down the progression of the disease.

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 adult dose of zidovudine for people weighing 30 kilograms or more is 600 mg taken by mouth daily. It may be taken as either 300 mg every 12 hours or 200 mg every eight hours.

For children and individuals weighing between 4 kilograms and 30 kilograms, the dosage is based on body weight or size. The recommended dose for children weighing between 4 kilograms and 9 kilograms is calculated as 24 mg per kilogram of body weight daily; the dose for individuals between 9 kg and 30 kg is 18 mg per kilogram of body weight daily. The recommended dose of zidovudine when calculated by body size is 480 mg per square metre (m²) of body surface area daily (to a maximum of 600 mg per day) as calculated by the doctor. Either calculation may be used, however the dose may not be the same. The total daily dose is usually divided up into two doses every 12 hours or three doses every eight hours.

For prevention of transmission of HIV infection to babies by pregnant women, 100 mg is taken by mouth 5 times daily starting 14 weeks into the pregnancy. During labour and delivery, zidovudine is given intravenously by the hospital until the baby is born. The child is then given a dose of zidovudine based on body weight every 6 hours until 6 weeks of age.

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.

Use an oral syringe to measure each dose of the liquid, as it gives a more accurate measurement than household teaspoons.

It is important to take this medication exactly as prescribed by your doctor. The effectiveness of the medication depends on having the right amount of zidovudine in the bloodstream. 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, protect it from light and moisture, and keep it out of the reach of children.

Capsules
Each gelatin capsule, with a white opaque cap and body, printed with "Wellcome" and a unicorn logo on the cap and "Y9C" and "100" on the body, contains 100 mg of zidovudine. Nonmedicinal ingredients: cornstarch, magnesium stearate, microcrystalline cellulose, and sodium starch glycolate; capsule shell: gelatin and edible black ink. The blue band around the capsule contains gelatin and indigotine.

I.V. injection
Each mL of solution contains 10 mg of zidovudine in water for injection. Hydrochloric acid or sodium hydroxide may have been added to adjust pH to approximately 5.5. The I.V. injection does not contain preservatives.

Syrup
Each 5 mL of colourless-to-pale-yellow, strawberry-flavoured syrup contains 50 mg of zidovudine. Nonmedicinal ingredients: candied sugar flavour, citric acid, glycerin, strawberry flavour, and sucrose. Sodium benzoate (0.2%) is added as a preservative and sodium hydroxide may have been added to adjust pH.

Do not take zidovudine if you:

• are allergic to zidovudine or any ingredients of the medication
• have a very low number of white or red blood cells in the bloodstream

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.

• breast enlargement (men)
• changed sense of taste
• changes in fingernail or toenail colour
• changes in skin colour
• chills
• cough
• difficulty concentrating
• dizziness
• fever
• headache (severe)
• heartburn
• gas
• loss of appetite
• nausea
• muscle aches
• sleepiness
• sweating
• 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:

• abdominal pain
• anxiety
• chest pain
• flu-like feelings (e.g., body aches, sore throat, weakness, nasal congestion, or runny nose)
• frequent urination
• loss of fat from arms, legs, and face
• numbness or tingling feeling
• signs of anemia (low red blood cells; e.g., pale skin, unusual tiredness, or weakness)
• signs of bleeding (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• signs of depression (e.g., changes in sleep, changes in weight, decreased interest in activities, poor concentration, thoughts of suicide)
• signs of infection (e.g., fever, chills, or sore throat)
• signs of liver problems (e.g., dark urine, diarrhea, loss of appetite, nausea, pale stools, vomiting, weight loss, yellowing of the skin or whites of the eyes)
• signs of muscle damage (e.g., unexplained muscle pain, tenderness or weakness, or brown or discoloured urine)
• skin rash (e.g., red, raised, or itchy skin)
• symptoms of immune reconstitution inflammatory syndrome (e.g., fever, redness, rash or swelling, fatigue, joint or muscle pain, numbness or weakness in the extremities, pounding heartbeat, chest pain)

Seek immediate medical attention if any of the following occur:

• convulsions (seizures)
• signs of lactic acidosis (e.g., abdominal pain, dizziness, increased breathing rate, nausea, rapid heart rate, unusual tiredness, vomiting)
• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, chills, fever, nausea, rapid heartbeat, swollen abdomen)
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, swelling of the face and throat)

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: Medications used to treat HIV can cause increased blood sugar levels. If you have high blood sugar or diabetes, 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 required.

Fat redistribution: Over time, this medication may change how fat is distributed in your body and may change your body shape. You may notice loss of fat from the legs, arms, and face.  Let your doctor know if you experience this effect.

Immune reconstitution inflammatory syndrome: This medication may cause immune reconstitution inflammatory syndrome, where signs and symptoms of inflammation from previous infections appear. These symptoms occur soon after starting anti-HIV medication and can vary. They are thought to occur as a result of the immune system improving and being able to fight infections that have been present without symptoms (such as pneumonia, herpes, or tuberculosis). Report any new symptoms to your doctor as soon as possible.

Kidney function: If you have reduced 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. People with severely reduced kidney function should not take this medication.

Lactic acidosis and enlarged fatty liver: Zidovudine can cause a rare but serious condition called lactic acidosis (build-up of lactic acid in the blood) together with an enlarged liver. This tends to happen more often to 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.

Liver function: Zidovudine is broken down by the liver so it can be removed from the body through the kidneys. Liver disease or reduced liver function may cause a build-up of zidovudine in the body and cause side effects. If you have liver disease or decreased liver 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.

If you experience symptoms of liver problems (e.g., abdominal pain, persistent vomiting, feeling unwell, fever, itching, yellowing of the skin and eyes, dark urine), contact your doctor immediately.

Pancreatitis (inflammation of the pancreas): Zidovudine may cause or worsen pancreatitis. If you have a history of or are at risk for developing pancreatitis, 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.

If you develop signs of pancreatitis (e.g., upper left abdominal pain, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen), contact your doctor.

Red blood cells: Pure red cell aplasia is a rare bone marrow disorder characterized by a reduction in red blood cells produced by the bone marrow. Symptoms include pallor, weakness, shortness of breath, heart palpitations, and decreased blood pressure. If you experience any of these symptoms contact your doctor immediately.

Zidovudine may also cause low levels of red blood cells without causing red cell aplasia. This usually happens after this medication has been taken for more than 4 to 6 weeks. Your doctor should order regular blood tests to monitor for changes in the numbers of blood cells during treatment. If you experience symptoms of reduced red blood cell count (anemia) such as shortness of breath, feeling unusually tired, or pale skin, contact your doctor as soon as possible.

Reduced white blood cells: Zidovudine can cause low levels of white blood cells. This usually happens after this medication has been taken for more than 4 to 6 weeks. Your doctor should order regular blood tests to monitor for changes in the numbers of blood cells during treatment. If you experience symptoms of an infection (e.g., fever, sore throat) contact your doctor immediately.

If you have low levels of white blood cells, your doctor may consider a different combination of medications to treat your condition.

Stopping the medication: If you stop taking this medication, your HIV 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: The use of zidovudine after the first 14 weeks of pregnancy does not appear to increase the risk of birth defects. Zidovudine is used by pregnant women with HIV infection to prevent transmission of the virus to the unborn child.

Breast-feeding: Zidovudine passes into breast milk. Women who have HIV infection are cautioned against breast-feeding because of the risk of passing HIV to a baby who does not have the infection.

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

• acyclovir
• atovaquone
• BCG
• cladribine
• clarithromycin
• clozapine
• deferiprone
• doxorubicin
• fluconazole
• ganciclovir
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• interferons
• mesalamine
• methadone
• olsalazine
• orlistat
• raltegravir
• ribavirin
• rifampin
• sulfasalazine
• teriflunomide
• trimethoprim
• valacyclovir
• valganciclovir
• valproic acid

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 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.