Drug Interactions: Resources for Patients and Professionals

Drug interactions are common in HIV treatment. But modern medical practice, with pressures to hurry due to cost control, may not leave enough time for physicians to make sure that they know about everything their patients are taking, and counsel them on potential risks. Not all drug interactions are harmful; some treatment combinations are designed to use interactions, and others can be adjusted to compensate for them. But patients may want to check their regimens to be aware of potential problems that they should bring to their doctor's attention.

Here are two AIDS-related drug interaction resources that are readily available. The first is written primarily for health care professionals, the other for patients.

* The Clinical Management of HIV/AIDS: Drug-Drug Interactions, by Charles Flexner, M.D., and Steven Piscitelli, Pharm. D.

This new one-hour CME (continuing medical education) module, written for physicians, pharmacists, and nurses but available to anyone through the World Wide Web, provides background on drug interactions as well as lists of what to watch out for. You can also submit your own regimen for an immediate computerized report on known potential interactions.

Most drug interactions fall into one or more of several classes, making them somewhat more predictable than might be expected. The background section of this training module--"How Drugs Interact: What You Need to Know" explains how most drugs are metabolized, and lists the five most important kinds of pharmacokinetic interactions, in which one drug affects the concentration of another ("inhibition of metabolism; induction of metabolism; altered drug absorption; inhibition of renal excretion; and displacement from plasma protein binding sites"). There are also pharmacodynamic interactions ("synergism or antagonism of drug effects, without alterations in the concentrations of either drug"). This section also describes the cytochrome P450 system, an important part of one of the two major ways the liver metabolizes drugs.

The next section, on questions health care providers need to ask themselves and their patients, lists practical issues which can be overlooked, such as:

- Prescription drugs from more than one physician and/or pharmacy;

- Non-prescription drugs including over-the-counter drugs, health foods and vitamins, alternative treatments, "underground" prescription or investigational drugs, illegal drugs, and investigational drugs through clinical trials.

- Pharmacy mistakes, such as confusing ritonavir with Retrovir® or Viramune® with Viracept®.

- Whether adherence to the drug regimen is particularly important.

- Overlapping adverse effects of some drugs (especially pancreatitis, renal dysfunction, bone marrow suppression, and peripheral neuropathy).

The next section, "What Drugs are Most Likely to Be Involved in Drug Interactions," is organized around "the 'red flag' list" of five different groups of drugs that need special attention: "P450 inducers, P450 inhibitors, metabolized drugs with narrow therapeutic indices, renally cleared drugs with narrow therapeutic indices, drugs with specific requirements for absorption." Alternatives are suggested for many of the medications which can be problematic.

There is also a drug-food interaction table, a sample daily dosing schedule, and links to other Web sites with more information.

This drug interaction guide is published by HealthCare Communications Group, and is available at (website no longer available).  The entire course can be printed easily, so if you do not have online access yourself, someone else could print the material for you.

* Project Inform's Drug Interactions Fact Sheet, by Ben Cheng

This simpler drug interaction guide has one page of introduction written for patients, and 17 pages of drug-drug interactions listed alphabetically by generic drug names. There is also a short glossary of terms used in describing the side effects. The introduction includes practical measures, such as the "brown bag medicine checkup--each time you see your health care provider, put all your medications, including over-the-counter and complementary products, in a bag and have your physician conduct a personalized review of your medicine for safety, appropriateness, compatibility, and instructions for use."

You can obtain a copy from Project Inform. Call the hotline, 800-822-7422 or 415-558-9051, 9 a.m. to 5 p.m. Pacific time Monday through Saturday--or write to Project Inform, 205 13th St., #2001, San Francisco, CA 94103--or get the information directly from http://www.projinf.org. The latest version, dated February 1998, will include information from the Retroviruses conference (Chicago, February 1-5).