Gleevec

What imatinib treats

Gleevec is the name most people know imatinib by, and the tablets sold here come in two strengths, 100mg and 400mg. It treats chronic myeloid leukaemia (CML), a cancer in which the bone marrow makes far too many white blood cells, and gastrointestinal stromal tumours (GIST), which begin in the wall of the stomach or bowel. Some rarer bone-marrow conditions driven by the same kind of gene fault are treated with it too.

How it works

Imatinib is a tyrosine kinase inhibitor. Tyrosine kinases are enzymes that behave like growth switches inside cells; in CML a gene fault builds one called BCR-ABL that never switches off, and in most GISTs a similar switch, KIT, is jammed on. Imatinib blocks those enzymes so the abnormal cells stop multiplying. It aims at particular switches, not at every fast-dividing cell, which separates it from older chemotherapy.

Taking it with your main meal

A dose goes down best with a meal and a full glass of water — food and fluid are what keep nausea and stomach pain to a minimum. The usual adult dose for chronic-phase CML and for GIST is 400mg once a day; if one large dose upsets your stomach, it can be split into two smaller ones. If swallowing is hard, a 100mg tablet can be stirred into a small glass of water or apple juice, and a 400mg tablet into a larger one; drink it straight away rather than saving it. Strips last best in a cool, dry drawer, since heat and damp are what shorten a tablet's shelf life.

Side effects worth knowing

Swelling is the most common: puffy eyelids, ankles and legs, sometimes a little weight gain. Nausea, diarrhoea, muscle cramps, aching bones, rash, headache and tiredness are frequent too, and most of these settle or ease with a smaller dose. Blood counts often drop, showing up as bruising, nosebleeds or infections that hang around. Less often, fluid gathers around the lungs or heart — breathlessness, fast weight gain — or the liver becomes inflamed, with yellowing of the eyes or skin, dark urine and pain under the right ribs. Bleeding that will not stop, black stools or a rash that blisters and spreads need urgent attention. Imatinib is not used in pregnancy, because it can harm the baby.

What else affects it

Liver enzymes of the CYP3A4 family break imatinib down, so anything that speeds those enzymes up or slows them down changes how much imatinib is in your body. Ketoconazole and itraconazole, used for fungal infections, push the level up; rifampicin, carbamazepine, phenytoin and St John's wort pull it down. Grapefruit and grapefruit juice push it up as well. Regular or high doses of paracetamol add to the strain on the liver.