Retrovir (zidovudine)

How does it work?

Retrovir capsules, tablets, oral solution and infusion all contain the active ingredient zidovudine (also known as azidothymidine or AZT), which is a type of medicine called a nucleoside reverse transcriptase inhibitor. It is used in the treatment of HIV (human immunodeficiency virus) infection.

AIDS (acquired immune deficiency syndrome) is caused by infection with HIV. This virus invades cells of the immune system, particularly the white blood cells known as CD4 T-helper lymphocytes. These cells normally work to activate other cells in the immune system to fight infection. Since HIV kills CD4 T-helper cells, over time the body becomes less able to fight the virus or subsequent infections.

Once the virus is inside the CD4 T-cell it multiplies. Part of the process of viral multiplication involves the conversion of the virus genetic material, RNA, into DNA. This is achieved by a compound essential to the virus, called reverse transcriptase. Reverse transcriptase is a compound known as an enzyme. Zidovudine works by blocking the action of this enzyme, thereby interfering with the conversion of viral RNA into DNA. This stops the virus from multiplying.

There is no cure for HIV, but zidovudine is one of a number of medications that lowers the amount of virus in the body (viral load) and slows the progression of the disease from HIV to AIDS. Zidovudine is used in conjunction with other anti-HIV drugs that attack the HIV virus in different ways. This helps prevent the virus becoming resistant to the medicine.

Zidovudine may be used on its own to treat pregnant women (over 14 weeks gestation) infected with HIV, in order to try and prevent transmission of HIV to the baby. (However, combination antiretroviral therapy maximises the chance of preventing transmission and also represents optimal therapy for the mother.) Zidovudine is also given to the baby once it is born, to treat any HIV infection that might have been passed to it from the mother during delivery.

What is it used for?

HIV infection.

Preventing HIV infection being passed from pregnant women to their developing babies (by treating pregnant women and their newborn infants).

Warning!

The HIV virus is very good at becoming resistant to anti-HIV medicines. For this reason it is very important that you carefully follow your doctor's instructions for taking your anti-HIV medicines, in order to maintain effective levels of the medicines in your blood. If the blood levels drop, the virus will be given more chance to replicate and develop resistance to the drugs. Skipping even a few doses increases the risk of treatment failure, so you should try to ensure that you take all your doses at the correct time, and that you visit your doctor for repeat prescriptions before you run out.

Treatment of HIV infection with anti-HIV medicines such as this one does not reduce the risk of transmitting the virus to other people through sexual contact or blood contamination. You should continue to use condoms to prevent transmitting the virus to your sexual partner.

Combination antiretroviral therapy has been associated with a redistribution of body fat (lipodystrophy) in people with HIV. The long-term consequences of this are currently unknown, however your doctor may wish to monitor your body fat, and the levels of lipids (eg cholesterol) and sugar (glucose) in your blood, and may prescribe additional medicines for any lipid disorders that occur during treatment with this medicine. Contact your doctor if you notice any changes in your body fat during treatment with your HIV medicines.

Some people being treated with combination antiretroviral therapy may develop a bone condition called osteonecrosis. This condition is caused by loss of blood supply to a bone, causing death of the bone tissue. The risk of the condition is thought to be increased by corticosteroid use, alcohol consumption, severe immunosuppression, higher body mass index, advanced HIV disease and long-term use of antiretroviral medicines. If you notice any joint stiffness, aches and pains (especially of the hip, knee and shoulder) or difficulty in movement while using this medicine, you should tell your doctor so this can be investigated.

While taking this medicine you should have regular blood tests to allow your doctor to monitor the number of blood cells in your blood. This is because zidovudine can sometimes cause a decrease in the numbers of white blood cells and red blood cells in the blood.

The class of medicines that zidovudine belongs to can cause a rare but serious condition called lactic acidosis, which is an excess of lactic acid in the blood, together with an enlarged liver. This side effect is more likely to occur in overweight women and people with liver disease (particularly hepatitis C treated with alpha interferon and ribavirin). If it occurs, lactic acidosis usually develops after a few months of treatment. Your doctor will monitor you for this side effect, but symptoms that might indicate it's development include rapid and/or deep breathing and non-specific symptoms such as feeling weak, sick or generally unwell, vomiting, abdominal pain, loss of appetite or weight loss. You should tell your doctor if you experience any of these.

If have any problems with your liver, in particular chronic hepatitis B or C, you should have regular blood tests to monitor your liver function while you are taking this medicine.

Use with caution in

Elderly people

Decreased kidney function

Decreased liver function

Enlarged liver (hepatomegaly)

Liver disease

Hepatitis, especially chronic hepatitis B or C

History of alcohol abuse

Obese women

Vitamin B12 deficiency.

Not to be used in

People with low haemoglobin levels

People with low levels of a type of white blood cell (neutrophil) in the blood

New born infants with high levels of bilirubin (jaundice) requiring treatment other than phototherapy (light therapy) or whose liver transaminase enzymes are five times greater than normal.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and Breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

Zidovudine can be taken by HIV-positive pregnant women to reduce the risk of transmitting HIV to their unborn child. However, it is important to carefully weigh the benefit of reducing the risk of HIV infection against the unknown possibility of the infant experiencing side effects in later life, and you should discuss this with your doctor. Zidovudine should only be used during the first trimester of pregnancy if the benefits to the mother outweigh any potential risks to the foetus during this vulnerable period. Again, seek further medical information and advice from your doctor.

It is recommended that women infected with the HIV virus must not breastfeed their infants under any circumstances, in order to avoid transmission of the virus to the baby. Seek medical advice from your doctor.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

Headache

Dizziness

Disturbances of the gut such as diarrhoea, constipation, nausea, vomiting or abdominal pain

Low red blood cell count (anaemia)

Decrease in the number of white blood cells in the blood (leucopenia)

Decrease in the number of a type of white blood cell (neutrophil) in the blood (neutropenia)

General feeling of being unwell (malaise)

Weakness or loss of strength (asthenia)

Fever (pyrexia)

Pain in the muscles (myalgia)

Shortness of breath

Rash or itching

Liver disorders

Inflammation of the pancreas (pancreatitis)

Pins and needles (paraesthesia)

Alteration in taste

Sleepiness (somnolence)

Difficulty in sleeping (insomnia)

Loss of appetite

Elevated levels of lactic acid in the blood (lactic acidosis)

Anxiety and depression

The side effects listed above may not include all of the side effects reported by the drug's manufacturer. For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

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