Treatment Review; August 1995

Both treatments are given by intravenous infusion. Both drugs require a catheter. A catheter is a small tube that is placed in a vein. This allows the drug to easily go into the vein. It also avoids having to find a new vein every time the drug needs to be given. Sometimes a catheter is placed in the arm. Powerful drugs like ganciclovir and foscarnet, however, can wear out the veins in the arm, so almost everyone who needs to take these drugs on an ongoing basis gets a permanent catheter.

Researchers are looking for treatments for CMV retinitis that aren't so demanding to take. A pill form of ganciclovir was recently approved by the Food and Drug Administration (FDA) for maintenance treatment of CMV retinitis. It is expected that this pill will also be approved for the prevention of CMV.

Studies have also shown that ganciclovir implants - small pellets of drug that are placed directly into the eye during a typically uncomplicated surgical procedure - are effective at treating CMV retinitis, although they are still being investigated. At this point it appears that the pellets only need to be inserted about once every six months - an obvious benefit over daily infusions.

One very important reason clinical trials are conducted is to determine the safety of a drug, including what side effects a drug might cause in the short and long term. Only one in ten experimental drugs makes it through the clinical trial process because testing shows that the drug is too toxic, or has other problems. Yet, many drugs used to treat cancer (chemotherapy) have well known toxicities. The FDA approves them, doctors prescribe them, and people with cancer are sometimes cured by them.

The seriousness of the problem for which the drug is being tested, such as life- threatening cancers or potentially fatal AIDS-related opportunistic infections, gives researchers license to push toxicity limits. Although few patients are eager to tolerate harsh or severe side effects, some are willing to tolerate the side effects if the benefit is great enough. There are also sometimes ways to lessen or eliminate the side effects of drugs. When foscarnet was first approved there were very real concerns about kidney toxicity. Doctors are often able to reduce possible side effects, however, by first giving infusions of saline solution (salt water) to hydrate the kidneys.

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