Drug interactions are a fact of life for anyone taking prescription medicine. Senior citizens, children, diabetics, and asthmatics could all experience drug interactions. Anyone taking multiple prescription drugs, or seeing more than one physician, is at risk. Even people taking only over-the-counter medications are not safe from risk. Moreover, many of today’s medication regimens are more complicated than even a few years ago.
At the same time, we understand the way drugs are metabolized better today and are doing more studies looking at interactions with food, other prescription drugs, over-the-counter medications, and alternative therapies. The use of recreational drugs and alcohol can also play a part in how prescription drug levels are affected.
Metabolism
After being ingested, drugs are processed by the body (metabolism), usually in the liver or kidneys. Certain drugs speed up this process and the amount of drug in the blood is lower than expected. Other times, drug level rises because metabolism is slowed, allowing more drug to be absorbed.
The stomach is another possible source of drug interactions. The amount of food and acid in the stomach can change the way drugs are absorbed because they require food or acid to work. High levels of fat can change the way drugs are absorbed.
The best thing to remember is to read each prescription label, even the little stickers on the bottles and the papers the pharmacist gives you about your medication. You will find very important information on how to take your medication correctly. If you still don’t have the answer, ask your pharmacist, nurse or physician to help.
Types of interactions
There are different types of drug interactions. Some interactions are actually beneficial. We have all discussed how important adherence is to a successful HIV regimen. Like adherence, drug interactions need to be considered to ensure that enough drug is in the bloodstream at all times, and to achieve viral suppression and prevent resistant virus.
One drug can change the amount of a second medication’s level of absorption. Too little drug absorbed could cause viral resistance and eventually virologic failure (in other words, a detectable viral load). Sometimes drugs combine together and raise the blood level of one or both of the medications.
In order for prescription drugs to be effective, the dose of drug level in the blood must be high enough to do its job, but not too high as to cause toxicities or unwanted side effects. Side effects may be an indication a drug interaction has occurred.
In many drugs used in treating other health conditions, the range between effective dose and toxic dose is large. In this case, interactions causing small changes in drug level may not change the expected outcome and not cause a problem.
With agents used in the treatment of HIV, this therapeutic range is very narrow. In other words, even a slight change in the amount of drug that gets into the blood can make a big difference in the effectiveness of the therapy.
Other drug interactions can alter side effects and your quality of life. If two drugs that each cause side effects when used alone are then prescribed together, their unwanted side effects are additive.
An example is when Zerit and Videx are used as part of a drug regimen. These two drugs can cause peripheral neuropathy, or tingling in the legs and arms. Managing side effects from taking only one of these drugs may be easy, but together, the combination may be too much to handle.Some drugs that interact can still be used if they are taken at different times.
Correct monitoring and communication with your providers will allow some drug combinations to be “watch and see.” There are variations from person to person, allowing some people to get away with using drugs that interact, but do not cause health problems.
Boosting
The use of a “boosted” protease inhibitor is an example of a good drug interaction. A small amount of ritonavir, a protease inhibitor, is added to many other protease inhibitors to increase blood levels to an effective and safe dose. By doing this, a lower dose of the other protease drug can be used with a small amount of ritonavir, having the same desired result. This will also reduce or eliminate side effects from taking higher doses of the same protease inhibitor.
Nexium and Prilosec
In the case of medications used for upset stomach and acid reflux (proton pump inhibitors and H-2 blockers), serious drug interactions can occur when used with certain protease inhibitors. Reyataz requires acid in the stomach for it to be metabolized. When taken with proton pump inhibitors like Nexium and Prilosec, acid secretion is stopped and Reyataz cannot be absorbed into the bloodstream.
Pepcid can be used only if you can separate the dose of the stomach medication and Reyataz by 12 hours. Speak to your pharmacist or physician before taking any prescription or over-the-counter antacids.
Herbs
Herbal medications are a little tricky. Since very few studies have been done with prescription drug interaction and herbal medications, the best advice is to avoid the more obvious problems (see Table 1). For all other products, be careful to learn about the normal doses. Everything in moderation! Even though the label on some of these natural products makes wild claims, stick to a reasonable dose. Remember, a lot of the health food and natural products do not go through any regulation or standards. There can be variations from batch to batch, and brand to brand. St. John’s wort, garlic supplements, milk thistle and grapefruit juice are the biggest offenders.
Alcohol
Alcohol is metabolized in the liver, the same place the drugs used in HIV are going to end up. If the liver is off “having cocktails”, it will not be able to process your meds correctly. A casual drink or two will probably not be a problem, but excessive alcohol use will compromise your ability to metabolize the drug regimen. Add on any hepatitis B or C and you know the liver is going to be very busy. Metabolism of protease inhibitors, non-nucleosides, and at least one nucleoside (Ziagen) may be affected by excessive use of alcohol. Pancreatitis can also be a concern with use of alcohol and a drug regimen which includes Videx (ddI).
Street drugs
Careful with the party pharmacy! The effects of marijuana or Marinol, mixed with protease inhibitors, commonly show up earlier because of the higher levels of THC when used together. Cocaine increases the rate of viral replication—enough said! Norvir (ritonavir), which is co-formulated in Kaletra, is the biggest culprit with many recreational drugs. See Table 2.
· Don’t take street drugs at the same time as your HAART (highly active antiretroviral therapy). But don’t be late with your HAART, get a sober friend to help!
· Drink lots of water.
· Avoid alcohol.
· Interactions will depend on the dose of recreational drugs. Because there will be variation in supplies, be careful!
· Whether or not you have eaten recently can change the effect of street drugs.
· Remember that controlled drug studies are usually not done with street drug interactions.
Fixed-dose combinations
Once-daily therapies and fixed dose combination drugs are common. When prescribed a fixed dose combination for the first time (Epzicom, Trizivir, Combivir, and Truvada) it may be advisable to take the drugs as individual products for a couple of months. If there is a drug interaction or unwanted side effect, it will be easier to eliminate the problem drug and the physician will be able to make a switch when possible. If everything is working out, move to the combined product.
Tips
The best way to evaluate drug interaction is to look at everything you are putting in your body. There are several good ways to evaluate your medication.
1. Learn the names of all of your medications.
When discussing drug interactions with your doctor or pharmacist, or looking up information on the Internet, you will need to know the brand name and the generic name of your medications so you will know what to look out for. Some over-the-counter drugs are the same as prescription drugs at different strength and with different names. Make a list if you have trouble pronouncing the drugs or remembering all of the names.
2. Tell your physician about everything you are taking.
Remember to think of prescriptions that you are given from other providers, samples that the doctors have dispensed, and even recreational drugs—be honest! It is important! What about those natural herbs and vitamin products? The only way anyone can evaluate problems caused by drug interaction is to have all of the pieces of the puzzle. Next time you visit your doctor’s office, bring a brown bag (or suitcase) filled with everything you are taking. Have him or her look it over.
Drug interactions are another great reason to find physicians and other health care providers who have experience in treating HIV. There is an art to working in the area of HIV/AIDS. An inexperienced doctor may not understand or consider the importance of combining drugs as someone who does this every day. For those of you not disclosing your HIV status and your HIV regimen to other providers—such as psychiatrists and dentists—you can see where this may become a problem. Doctors give treatments in their offices, or hand out free samples, without being aware there could be serious results.
3. Keep a list of all of your medications on you.
In case of emergency, the treating physician will need to know what medications you are taking. Emergency medical cards or wrist bracelets can also be customized to hold your health information. This is especially true of anyone taking Kaletra or Norvir, because of the longer list of known interactions with those medications. Norvir, which is also in Kaletra, works differently from other HIV protease inhibitors.
4. Use one pharmacy.
This may be difficult because some of you are required to get your meds through ADAP pharmacies. Either way, tell your pharmacist everything you are taking—at your regular pharmacy and at your ADAP pharmacy. Most pharmacists have computer programs that sort out some of the problems that a doctor may not have known about. By using one pharmacy, this can be done very easily.
Sometimes drug interactions are caught at the pharmacy before you are even aware that there is a problem. The pharmacist will usually call the physician to discuss a change in therapy before filling your prescription. When in doubt, ask questions. If you are not comfortable speaking to a pharmacist at the store, give them a call when you get home. Get to know your pharmacist; ask your pharmacy to help you with information you need. If they do not know, a good pharmacist will get back to you with the answers. In emergencies, a 24-hour pharmacy will be able to access your prescription records at any time.
Double-check any over the counter drug purchases with your pharmacist or physician. This is now more important than ever as many popular drugs are no longer requiring a doctor’s order. You can go into any gas station or convenience store and get many products that only yesterday required you to wait weeks for a doctor’s appointment.
5. Use Internet resources.
There are many websites that can help you sort out the potential drug interactions yourself. Use these tools as a guide to ask your physician or pharmacist about. Do not make any changes in your therapy until your doctor tells you to do it. With some drug interactions, there may be no need to adjust the dose of either drug. See Drug Interaction Websites.
Common HIV drug interactions
The drug interactions listed in this article or charts are only a small fraction of possible ones that exist. Please check with your physician or pharmacist if you have any questions about these interactions or any others that are not listed. See Table 3.
Conclusion
Drug interactions are here to stay in the treatment of HIV/AIDS. New drugs are being developed each year to stay one step ahead of resistant virus. With all of our advances and the excitement about new treatment options, drug interactions are becoming even more important. Keep on top of your treatment providers to continually check for potential combinations that may be troublesome.
Glen Pietrandoni, R.Ph., is the manager of HIV/AIDS programs for Walgreens Specialty Pharmacy in the Chicago area. E-mail Glen.Pietrandoni@walgreens.com.
|
