Neither of these drugs will cure CMV, but they can stop CMV from getting worse. Both drugs require a daily infusion, meaning that the drug has to be given in the vein every day for about 2 - 4 hours. The catheter must be bandaged and kept clean and dry. Because the drugs only slow down the illness, treatment must continue for the rest of your life and you must see your doctor regularly to make certain that the CMV illness is not getting worse. Very often these drugs will not work well or will have toxic side effects that make you sick.
Some doctors use both drugs in combination.
Some studies have shown foscarnet to be more effective than gancyclovir, but it can also have more toxic side effects and it requires a more lengthy, daily infusion. There are medicines, which might be better and easier to take, that are being tested in clinical trials now. It is usually reversible if you stop taking the drug. AZT can also cause neutropenia, so if taking both AZT and gancyclovir, close monitoring of your white blood cell count is very important. Foscarnet can cause serious kidney damage and nausea and skin ulcerations.