How does it work?

Videx chewable or dispersible tablets contain the activeingredient didanosine (also known as ddi), which is a type of medicine called anucleoside reverse transcriptase inhibitor. It is used in the treatment of HIV(human immunodeficiency virus) infection.

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

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

There is no cure for HIV, but didanosine is one of a number ofmedications that lowers the amount of virus in the body (viral load) and slowsthe progression of the disease from HIV to AIDS. Didanosine is used inconjunction with other anti-HIV drugs that attack the HIV virus in differentways. This helps prevent the virus becoming resistant to themedicine.

Didanosine can be broken down and made ineffective by the acidin the stomach. For this reason, Videx chewable/dispersible tablets contain anantacid that neutralises the acid in the stomach. This protects the didanosinefrom the stomach acid. To ensure that there is sufficient antacid to protectthe didanosine, each dose must be taken as a minimum of two tablets. (Childrenunder one year can receive a one tablet dose.)

What is it used for?

• HIV infection.

Warning!

• Videx chewable/dispersible tablets should be taken on an empty stomach, because the presence of food in the stomach can reduce the absorption of the didanosine. The tablets should be taken at least 30 minutes before food. They should be thoroughly chewed, or dispersed in water as directed by your pharmacist. If the tablets are dispersed, the solution should be drunk immediately. Clear apple juice may be added to the solution for flavouring if desired.
• 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.
• You should have regular blood tests to monitor your liver function while you are taking this medicine. This is especially important if you already have any problems with your liver, in particular chronic hepatitis B or C. Symptoms that may suggest a liver problem include persistent nausea and vomiting, abdominal pain, or the development of jaundice (a yellow colouring to the skin and the whites of the eyes). Consult your doctor if you experience any of these symptoms.
• Your doctor may also want you to have regular blood tests during treatment to check for a side effect called pancreatitis (inflammation of the pancreas). You should let your doctor know if you experience sudden unexplained stomach or abdominal pain, nausea or vomiting while taking this medicine, as these could be symptoms of pancreatitis.
• It is recommended that you have eye examinations every six months while you are taking this medicine, as it can sometimes cause eye problems. Consult your doctor if you experience any disturbances in your vision while taking this medicine. This is particularly important for children.
• Consult your doctor immediately if you experience abnormal sensations in your feet and/or hands while taking this medicine, for example, numbness, tingling or burning sensations or pain, as this could be indicative of a nerve problem called peripheral neuropathy.
• The class of medicines that didanosine 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.

Use with caution in

• Decreased kidney function
• Decreased liver function
• Liver disease
• Enlarged liver (hepatomegaly)
• Hepatitis, especially chronic hepatitis B or C
• History of alcohol abuse
• Obese women
• High blood uric acid level (hyperuricaemia)
• History of pancreatitis
• Raised triglyceride levels in the blood (hypertriglyceridaemia)
• An inherited disorder of protein metabolism called phenylketonuria (Videx tablets contain aspartame)
• Intolerance to fructose (Videx tablets contain sorbitol).

Not to be used in

• Known sensitivity or allergy to any ingredient.
• Videx tablets are not recommended for children under three months of age.

This medicine should not be used if you are allergic to one orany of its ingredients. Please inform your doctor or pharmacist if you havepreviously experienced such anallergy.If you feel you haveexperienced an allergic reaction, stop using this medicine and inform yourdoctor or pharmacist immediately.

Pregnancy and Breastfeeding

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

• The safety of this medicine in pregnancy has not been established. It should therefore be used with caution during pregnancy, and only if the benefits to the mother outweigh any risks to the foetus. Seek medical 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.

Label warnings

• Take this medication on an empty stomach.

Side effects

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

• Disturbances of the gut such as nausea, vomiting, diarrhoea or abdominal pain
• Headache
• Rash
• Fatigue
• Disorder of the peripheral nerves causing weakness and numbness (peripheral neuropathy)
• Dry mouth
• Weakness or loss of strength (asthenia)
• Loss of appetite
• Pain in the muscles and joints
• Elevated levels of lactic acid in the blood (lactic acidosis)
• Raised cholesterol levels
• Diabetes
• Inflammation of the pancreas (pancreatitis)
• High blood uric acid level (hyperuricaemia) which can cause kidney problems and gout
• Hair loss (alopecia)
• Changes to the retina and optic nerve of the eye
• Dry eyes
• Liver disorders
• Blood disorders

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

How can this medicine affect other medicines?

You should tell your doctor or pharmacist what medicines you areusing, particularly those listed below, before you start treatment with thismedicine. This includes those bought without a prescription and herbalmedicines. Likewise, check with your doctor or pharmacist before starting anynew medicines while you are taking this medicine, so they can check that thecombination is safe.

Videx chewable/dispersible tablets contain an antacid to stopthe active ingredient didanosine being broken down by the acid in the stomach.For this reason, medicines whose absorption can be affected by antacids shouldnot be taken within two hours of taking the chewable/dispersible tablets. Thesemedicines include the following:

• azole-type antifungals, eg ketoconazole and itraconazole
• tetracycline-type antibiotics, eg tetracycline, doxycycline, minocycline
• some quinolone-type antibiotics, eg ciprofloxacin.

The following medicines may increase the blood level ofdidanosine and people who are taking any of these should be monitored forincreased side effects of didanosine:

• allopurinol
• ganciclovir.

The blood level of didanosine may also be increased if it istaken in combination with another anti-HIV medicine called tenofovir (Viread).This may increase the risk of didanosine side effects. Studies using lowerdoses of didanosine with tenofovir to avoid this problem have shown a high rateof early virological failure and emergence of resistance to the medicine. Forthis reason, using tenofovir in combination with didanosine is not recommended,particularly in people with a high viral load and low CD4 count. If your doctorfeels it is necessary to take these medicines together, your viral load and CD4counts should be regularly checked, and you should be monitored for anypossible side effects of didanosine, in particular pancreatitis and lacticacidosis.

There have been reports of a high rate of virological failureand the emergence of resistance at early stage when didanosine was combinedwith lamivudine plus tenofovir as triple therapy.

Hydroxyurea (hydroxycarbamide) is not recommended for use incombination with this medicine, as it may increase the risk of liver problems,pancreatitis and peripheral neuropathy.

Other medicines containing the same active ingredient