by Rachel Therrien, pharmacist — published October 2012
Rachel Therrien is a pharmacist specializing in HIV and AIDS at the Unité hospitalière de recherche, d’enseignement et de soins sur le sida (UHRESS) in Montreal. She is also the codeveloper of the online HIV Medication Guide, a prize-winning resource that provides information on ARVs.
Taking medications for conditions other than HIV can be complicated by interactions between antiretrovirals (ARVs) and these other drugs. This article looks at some of the most common interactions and emphasizes the importance of talking to your doctor and pharmacist about any new drug.
What is a drug interaction?
Drug interactions occur when one drug changes the concentration of another drug in your blood. “Drug A” can
increase the concentration of “Drug B,” which puts you at greater risk of side effects or toxicities from Drug B. Or Drug A can decrease the concentration of Drug B and make Drug B less effective.
Another form of interaction is when two medications taken together have additive (1+1=2), synergistic (1+1=3) or antagonistic (1+1=0) effects. For example, if two different medications each increase the risk of anemia, this side effect is more likely to occur if you’re taking both medications.
Some ARVs present a greater risk of interaction than others. For example, nonnucleoside reverse transcriptase inhibitors (NNRTIs) and especially protease inhibitors (PIs) are more likely than other ARVs to interact with other medications.
Interactions aren’t limited to prescription medications; they can also occur with over-the-counter medicines such as anti-inflammatories (e.g. ibuprofen [Advil® or Motrin®]), or drugs for digestive problems like ranitidine (Zantac®) or famotidine (Pepcid®). Natural or herbal remedies and recreational or street drugs can interact with ARVs as well.
It’s therefore very important to talk to you doctor and pharmacist about all the drugs you’re taking. Be sure your doctor knows about prescriptions you’ve received from other doctors. Ask your pharmacist to check for possible interactions every time you add or stop a medication.
It helps to obtain all your drugs from a single pharmacy so that your pharmacist has your complete record and is equipped to detect interactions before they cause problems.
What to do about interactions?
How the interaction is treated depends on a number of factors and may differ from one person to the next. Your doctor may want to see you more often to monitor the drug’s effects and take a blood test to measure the concentration of certain medications in your blood. Your medication dosages may be changed or you may need to switch to another medication.
Interactions can be complex and your doctor may seek advice from the healthcare team and outside experts.
Some common interactions you should know about
Antacids
Atazanavir (Reyataz®) -especially when it is given alone without ritonavir (Norvir®) – and rilpivirine (Edurant® or Complera®) can interact with different types of medications used to reduce stomach acidity. Some antacids should be avoided when you are taking these ARVs and alternatives will be suggested; others can be taken but must be spaced apart (e.g. taken 12 hours before or after the ARV) to avoid lowering the levels of your ARVs.
Medications used in epilepsy, as mood stabilizers or for pain control
Carbamazepine (Tegretol®) and phenytoin (Dilantin®) have different indications and can speed up the metabolism of certain ARVs, making them less effective. Your HIV treating doctor must be told about the prescription of any of these medications.
A blood test enables your doctor to measure the level of certain ARVs in your blood and he or she may increase the dosage of one or more of them if necessary. Your doctor may also decide to modify your HIV treatment or choose an alternative to phenytoin or carbamazepine.
Medications for anxiety or insomnia
The concentration of some medications in the benzodiazepine class, such as diazepam (Valium®), clonazepam (Rivotril®), and flurazepam (Dalmane®), can be increased in your blood when combined with PIs. There’s a risk of excessive sedation (sleepiness), confusion and even breathing problems. These medications should be avoided or used at the lowest possible effective dose if you are also taking PIs. Among the benzodiazepines that can be safely used alongside PIs are lorazepam (Ativan®), oxazepam (Serax®) and temazepam (Restoril®).
Medications for erectile dysfunction
Like the benzodiazepines discussed above, sildenafil (Viagra®), tadalafil (Cialis®) and vardenafil (Levitra®) can accumulate in the blood if you’re also taking PIs. Dosages of these medications need to be decreased by a lot to avoid the appearance of serious side effects. For example, it is recommended that you never take more than 25 mg of Viagra within a 48-hour period if you are taking a PI.
Inhalers (pumps) for asthma and other lung problems
Fluticasone (Flovent®, Advair®) is an inhaled corticosteroid. It is absorbed primarily in the lungs, but a small quantity makes its way into the blood. When it’s taken alongside PIs, fluticasone can become overly concentrated in the blood. This can lead to symptoms associated with Cushing’s syndrome (too much cortisol in the blood) that can include weight gain, a moon-shaped face, buffalo hump (a lump of fat on the back of the neck or between the shoulders), a larger belly, high blood pressure, insomnia and nervousness. Adrenal function can also be disturbed, causing serious problems if fluticasone is stopped suddenly.
For this reason, pumps that contain fluticasone must be avoided if you’re taking PIs. If possible, your doctor should avoid prescribing corticosteroids in any form and find an alternative, or opt for an ARV regimen without PIs.
If you can’t avoid the combination of corticosteroids and PIs, pumps with other corticosteroids such as beclomethasone (Beconase®), budesonide (Pulmicort®) and ciclesonide (Alvesco®) should be used at the lowest possible dosages. These are safer alternatives, though Cushing-like symptoms have also been reported with budesonide. If you must take one of these inhaled corticosteroids, it’s important that you tell your doctor if you notice that you’ve gained weight recently or have any of the other Cushing’s-like symptoms mentioned earlier. Your doctor may also do a blood test to measure the cortisol in your blood and check your adrenal function.
Preventing interactions
There are many more interactions than we can look at in detail here. For more complete and regularly updated information on interactions between particular drugs, you can consult the websites mentioned in the sidebar.
The most important thing is to communicate openly with your doctor and pharmacist. They can help to detect interactions and manage them quickly to prevent a decrease in your medications’ effectiveness or the appearance of serious side effects.
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