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 . If you are concerned about side effects, discuss the risks and benefits of with your doctor.

The following side effects have been reported by at least 1% of people taking . 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
• cough
• difficulty concentrating
• dizziness
• Fever
• headache (severe)
• heartburn
• loss of appetite
• nausea
• muscle aches
• sleepiness
• 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
• increased fat on the upper back, neck, breasts, and around the trunk and loss of fat from the legs, arms, 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)
• skin rash

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 .

Each white capsule, identified "APO Z100", contains 100 mg of zidovudine. Nonmedicinal ingredients: microcrystalline cellulose, starch, stearic acid, and colloidal silicon dioxide. The capsule, imprinted with edible black ink, contains gelatin, titanium dioxide, methyl parabens, propyl parabens, and sodium lauryl sulfate.

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

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

• acyclovir
• atovaquine
• Azathioprine
• BCG
• clarithromycin
• Clozapine
• Cyclophosphamide
• Deferiprone
• dipyrone
• Doxorubicin
• fluconazole
• flucytosine
• Ganciclovir
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• interferon alfa
• interferon beta
• lamivudine
• Methadone
• Mercaptopurine
• Methotrexate
• Orlistat
• Phenytoin
• raltegravir
• ribavirin
• rifabutin
• rifampin
• rifapentine
• stavudine
• Teriflunomide
• trimethoprim-sulfamethoxazole
• Valacyclovir
• 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 . 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.

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 .

Fat redistribution: Over time, may change how fat is distributed in your body and may change your body shape. You may notice increased fat in the upper back and neck, breast, around the back, chest, and stomach area; or loss of fat from the legs, arms, and face. The long-term effects of this are not known.

Immune reconstitution syndrome: may cause immune reconstitution 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 may affect your medical condition, how your medical condition may affect the dosing and effectiveness of , and whether any special monitoring is needed. People with severely reduced kidney function should not take .

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 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.

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 may affect your medical condition, how your medical condition may affect the dosing and effectiveness of , 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 may affect your medical condition, how your medical condition may affect the dosing and effectiveness of , 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 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 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 white blood cells, your doctor may consider a different combination of medications to treat your condition.

Stopping the medication: If you stop taking , 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.

Zidovudine belongs to the class of antiretroviral medications called nucleoside reverse transcriptase inhibitors (NRTIs). It is used either alone or 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.

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

Your doctor may have suggested 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 , speak to your doctor. Do not stop taking without consulting your doctor.

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