Drug Interactions

When choosing the drugs that will make up your HAART combination, it will be very important to look at the possibility of drug interactions. Interactions can occur when one medication affects how another is absorbed, broken down (metabolized), distributed or flushed out of the body. This can work either well or badly.

Here is an example of a combination that works well: Ritonavir (Norvir), a protease inhibitor (PI), tends to slow down (inhibit) the breakdown of certain other protease inhibitors in the liver, boosting their levels in the blood. The effect of a boosted PI regimen is a positive one, with some of the following advantages:

• Ritonavir raises levels of the boosted PI to higher than normal, resulting in an increase in anti-HIV activity.
  Advertisement
• Ritonavir also prolongs the time that the boosted PI remains in the blood, resulting in a twice- or even once-daily regimen.

The opposite effect can also happen. One drug may speed up the breakdown of another, with the result being that the second drug's effectiveness is diminished, often leading to the development of viral resistance to that drug.

Interactions can also change the effect that drugs have, sometimes worsening them. For example, if two drugs both have a tendency to cause the same type of toxicity, using them together may greatly increase the chances that a serious side effect will occur. For example, the nucleoside analogue "d" drugs -- ddC, ddI and d4T -- are all likely to cause neuropathy. Combining them makes the risk much higher, something to bear in mind if any of these drugs are used together.

It is important to always check for interactions between all the drugs that you are taking, not just the antiretrovirals. With so many different medications being used for antiretroviral therapy and for treatment or prevention of opportunistic infections and for treatment of drug side effects or other symptoms, the chances for interactions seem to increase all the time. And, as though that's not complicated enough, interactions can occur not only between prescription medications but also between a medication and an over-the-counter agent, an herb, a food, or a recreational drug.

Drug interactions may not always be obvious. They can take various forms, with some occurring immediately after you first combine the drugs, and others not causing any noticeable problem for weeks or longer. In some cases, there are drugs which absolutely cannot be used together. In other cases, it may be possible to use certain drugs together as long as certain adjustments (timing of when they're taken, dosages, etc.) are made.

There are no perfect ways to prevent all possible drug interactions because we don't have perfect knowledge on this. Most studies have only looked at the interactions between two drugs at a time, and many people are taking far more than that. Adding in the possibility of interactions between multiple drugs and foods and herbs and, well, we think you get the picture. There may always be some risk that an interaction won't be predicted.

However, there are several steps you can take to try to ensure that it is safe to combine all the things you're taking:

• First and foremost, make sure that your doctor is aware of every single thing you're taking -- whether it's a prescription drug, an over-the-counter therapy, an herb, a nutrient or anything else. The simplest way to do this is to do a "brown bag" checkup -- each time you see your doctor, put all your medications, including over-the-counter and complementary products, in a bag and have him or her conduct a personalized review of your medicine for safety, appropriateness, compatibility and instructions for use. If you know your medical visits are often too rushed for this, be sure to request the extra time when you make your appointment. You can do the same kind of visit with your pharmacist, who may, in some cases, be better informed of all the latest news on drug interactions than other health care providers. And many pharmacies now have computerized drug interaction programs that will warn of any interactions if they have a complete list of all agents being taken.

• Second, every time you are prescribed a new medication, or decide that you wish to add an herb or an over-the-counter agent of any kind to the list of things you're taking, discuss with your doctor whether it can be combined safely with your other therapies. And don't count on your doctor knowing your whole history by heart. That chart may be five inches thick, and your doctor may have seen 400 patients since your last visit. So remind her or him of your brown-bag list.

• Third, you can do some checking on your own with a great website resource available at www.aidsmeds.com. At this site, click on "Check Your Meds." It will allow you to enter all your drugs plus nutrients plus herbs plus various foods (like garlic or grapefruit, both known causes of certain interactions), and then give you information on all the possible interactions known between all these things. It is a great resource.