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Drug Interactions Associated with the Protease Inhibitors

Treatment Watch

May 1998

A note from TheBody.com: Since this article was written, the HIV pandemic has changed, as has our understanding of HIV/AIDS and its treatment. As a result, parts of this article may be outdated. Please keep this in mind, and be sure to visit other parts of our site for more recent information!

Tips on how to avoid the possibility of drug interactions by thoroughly communicating with your care providers were covered in an article published in the April edition of Positive Living. In this article, Glenn Gaylord looks at the various drug interactions associated with protease inhibitors, Crixivan (indinavir), Invirase/Fortovase (saquinavir mesylate and saquinavir respectively), Viracept (nelfinavir mesylate), and Norvir (ritonavir).


As a quick generalization, Norvir is the protease inhibitor most likely to either interfere with the metabolism of other drugs or to have drug interaction concerns, while Crixivan and Viracept have concerns to a lesser degree. Both Invirase and its soft-gel formulation, Fortovase, have less potential to cause drug interactions than the others.

All of the protease inhibitors, however, affect liver enzymes, which can determine the way other drugs are processed, thus leading to drug interactions.

It is important to note, however, that the term "drug interaction" does not always refer to harmful combinations. At times, a combination of drugs will enhance each other's bioavailability. Studies have shown, for example, that the combination of saquinavir and ritonavir can produce a beneficial drug interaction.

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The chart on this page detail some of the major drugs that one should avoid taking with protease inhibitors:


Drugs to avoid if you use Crixivan (indinavir)
Drug Class Generic Name Brand Name
anticonvulsantphenobarbitalQuadrinal, Mudrane
 phenytoinDilantin
 carbamazepineTegretol
anti-nauseacisapridePropulsid
anti-mycobacterialrifampinRifadin
cold and allergy (antihistamine)terfenadineSeldane (no longer available)
 astemizoleHismanal
psychotropic (sedative / hypnotic)midazolamVersed
 triazolamHalcion
 
Drugs to avoid if you use Invirase / Fortovase (saquinavir)
Drug Class Generic Name Brand Name
anti-mycobacterialrifabutinMycobutin
 rifampinRifadin
anti-convulsantsphenobarbitalQuadrinal, Mudrane
 phenytoinDilantin
 carbamazepineTegretol
anti-nauseacisapridePropulsid
cold and allergy (antihistamine)astemizoleHismanal
 terfenadineSeldane
 
Drugs to avoid if you use Viracept (nelfinavir)
Drug Class Generic Name Brand Name
anti-nauseacisapridePropulsid
anti-mycobacterialrifampinRifadin
antiseizurephenobarbitalQuadrinal
 phenytoinDilantin
 carbamazepineTegretol
cardiovascular (antarrhythmic)amiodaroneCordarone
 quinidineQuinidex, Quiniglute
cold and allergy (antihistamine)astemizoleHismanal
 terfenadineSeldane
oral contraceptivesethinyl estradiolEstinyl, Ovcon-35
 norethindroneNorlutin
sedativemidazolamVersed
 triazolamHalcion
 
Drugs to avoid if you use Norvir (ritonavir)
Drug Class Generic Name Brand Name
analgesicmeperidineDemerol
 piroxicamFeldene
 propoxypheneDarvon
cardiovascular (antarrhythmic)amiodaroneCordarone
 encainideEnkaid
 flecainideTambacor
 propafenoneRhythmol
 quinidineQuinidex, Quiniglute
anti-alcohol addictiondisulfiramAntabuse
anti-mycobacterialrifabutinMycobutin
 rifampinRifadin
cardiovascular (calcium channel blocker)bepridilVascor
cold and allergy (antihistamine)astemizoleHismanal
antimigrainedihydroergotamineD.H.E. 45
 ergotaminevarious
anti-nauseacisapridePropulsid
anti-bacterialmetronidazoleFlagyl
anti-depressantbupropionWellbutrin, Zyban
anti-psychoticspimozideOrap
 clozapineClozaril
oral contraceptivesethinyl estradiolEstinyl, Ovcon-35
psychotropic (sedative / hypnotic)alprazolamXanax
 clorazepateTranxene
 diazepamValium
 estazolamProsom
 flurazepamDalmane
 midazolamVersed
 triazolamHalcion
 zolpidemAmbien


Let's look at the drugs that appear on all four lists:

  • Rifadin (rifampin). This antibiotic is designed to treat mycobacterial infections such as tuberculosis and MAC (Mycobacterium Avium Complex), and is known to decrease the levels of all protease inhibitors. The sister drug to rifampin, Mycobutin (rifabutin), should not be taken with ritonavir as it may increase side effects and toxicity. In some cases, care providers have been known to treat MAC with Rifadin and/or Mycobutin while curtailing any protease inhibitor therapy and will only introduce protease once the MAC treatment has stopped.

  • Hismanal (astemizole) and Seldane (terfenadine). Hismanal and Seldane are fairly new antihistamines that have the distinct characteristic of not causing as much drowsiness as their counterparts. Seldane has been used in the past in people with HIV to reduce such side effects as rashes, swelling and HIVes. Both drugs have shown, however, to increase side effects when taken with protease inhibitors, and Seldane has, in fact, been removed from the market.

  • Halcion, Xanax, Valium and Demerol are fairly common sedatives and analgesics found on some of the lists. Halcion, typically prescribed to treat insomnia, has been shown to increase the risk of toxicity with all of the protease inhibitors except Invirase/Fortovase while Xanax and Valium, anti-anxiety medications, have similar concerns when taken with ritonavir. Demerol, an opium-derived pain killer, and often used as a morphine substitute, has shown to produce adverse side effects when administered with ritonavir. Finally, it has been determined that levels of oral contraceptives (birth control pills) can be reduced by as much as 40 percent when taken with Viracept and Norvir, which may result in either an increased dosage of the oral contraceptive or a different combination choice.

This article is by no means a complete listing of the drug interactions involving protease inhibitors. If you have an area of concern, check with your care provider, pharmacist and treatment advocate before taking any medications.


Glenn Gaylord is a treatment advocate at AIDS Project Los Angeles. He can be reached by e-mail at GGaylord@APLA.org or by phoning (213) 993-1509.


This article has been reprinted at The Body with the permission of AIDS Project Los Angeles (APLA).

A note from TheBody.com: Since this article was written, the HIV pandemic has changed, as has our understanding of HIV/AIDS and its treatment. As a result, parts of this article may be outdated. Please keep this in mind, and be sure to visit other parts of our site for more recent information!



  
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This article was provided by AIDS Project Los Angeles. It is a part of the publication Positive Living.
 
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