Prevall Oral Suspension is a class of anti-cancer drugs that belongs to the category of medicines known as purine antagonists, containing the active ingredient Mercaptopurine. It is used in the treatment of acute lymphoblastic leukaemia. Acute lymphoblastic leukaemia (ALL) is a type of cancer that affects the blood and bone marrow. It is characterised by the overproduction of immature white blood cells, known as lymphoblast, which are unable to function properly and accumulate in the bone marrow and blood. If you are going to have a vaccination, speak to your doctor or nurse before you have it. When you take this drug, you should not have a live vaccine (like polio, measles, mumps and rubella.) until advised it is safe to do so by your doctor. This is because some vaccines may give you an infection if you have them while you are taking this drug. Do not get vaccinated with yellow fever vaccine while you are taking this drug because it may lead to serious illness. Your doctor may also ask for other blood and urine tests to monitor how your kidneys are working and to measure uric acid levels. Uric acid is a natural substance made in your body and levels of uric acid can rise while you are taking this drug. High levels of uric acid may damage your kidneys, so your doctor may sometimes change your dose of the drug as a result of these tests. It is probably advisable to start with lower doses in patients with impaired renal function, due to slower elimination of the drug and metabolites and a greater cumulative effect. Consideration should be given to reducing the dosage in patients with impaired hepatic function. During the treatment, your doctor may periodically monitor your white blood cell counts, platelets, blood sugar, electrolytes and kidney parameters to prevent serious complications. Inform to the doctor if you have been diagnosed with liver disorders, heart failure, high blood cholesterol levels, or hypertension before starting this treatment.This medicine has the potential to cause liver problems, so your doctor will carry out weekly liver function tests when you are taking this drug. Report to your doctor if you experience any hypersensitive reactions like itchy skin or rashes, while taking this medicine. This tablet contains lactose as an inactive ingredient in which the body is unable to digest lactose, a sugar found in milk and dairy products. It can cause symptoms such as bloating, and abdominal pain. If you have lactose intolerance, inform your doctor before starting this therapy.