HIV: The Quick and Dirty of Drug Interactions

Screening for drug interactions is one of the things that pharmacists do best, but one of the most formidable tasks that pharmacists face is screening for drug interactions when the patient presents with a fistful of prescriptions.

We asked Jeffrey R. Aeschlimann, PharmD, an infectious disease specialist who is on the faculty of the University of Connecticut's Schools of Medicine and Pharmacy, to answer questions about drug interactions in patients with HIV.

Aeschlimann acknowledges that drug interactions are worrisome in patients with HIV who are undergoing active treatment. These drug interactions can be definite, probable, or possible. Differentiating between the various levels of interactions is critical. Table 1 presents a concise summary of the most common antiviral drug interactions, but is not complete. Aeschlimann advises pharmacists to memorize the drug interactions that are most likely to occur, listed in column 1 of the table. He reminds pharmacists to consult the antiretroviral's complete prescribing information if they have any questions about potential drug interactions.

Table 1. Most Common Antiretroviral Drug Interactions^1,2

Column 1: Definite

Column 2: Probable

Column 3: Possible

▪ PDE5 inhibitors and PIs or cobicistat

▪ Fluticasone and PIs or cobicistat

▪ Methadone and certain PIs or NNRTIs

▪ Rifamycin and PIs, NNRTIs, cobicistat, or maraviroc

▪ Specific combinations of HIV agents (eg, certain PIs or integrase inhibitors with NNRTIs, maraviroc with PIs or NNRTIs, tenofovir with atazanavir)

▪ Statins with PIs or cobicistat

▪ St. John's wort and cobicistat

▪ Antidepressants and PIs or NNRTIs

▪ Select antiepileptic medications and PIs, NNRTIs, or cobicistat

▪ Certain antifungal agents and PIs, NNRTIs, or cobicistat (except in the case of voriconazole, for which definite information on interactions is available)

▪ Oral contraceptives and PIs or cobicistat

▪ Polyvalent cations (eg, calcium, iron, cation-containing antacids) and integrase inhibitors

▪ Proton pump inhibitors (PPIs) or H-2 blockers and atazanavir or rilpivirine

▪ St. John's wort and integrase inhibitors

▪ Warfarin and PIs, NNRTIs, or cobicistat

▪ Antidiabetic medications and PIs or NNRTIs

▪ Antipsychotic agents and PIs, NNRTIs, or cobicistat

▪ Herbal products (except St. John's wort; see column 1) and PIs, NNRTIs, or cobicistat

NNRTI = non-nucleoside reverse transcriptase inhibitors; PI = protease inhibitor; ppi = proton pump inhibitor

Pharmacists often identify drug interactions using their community pharmacy proprietary dispensing software. Aeschlimann indicates that pharmacists need to know their systems' strengths and limitations. They especially need to be aware of how frequently the proprietary dispensing software is updated with new or emerging drug interactions. Pharmacists can supplement built-in drug interaction systems with screening tools that have been developed specifically for HIV medications. He recommends 3 such systems (see Table 2) to augment proprietary systems.

Table 2. Drug Interaction Web Sites for HIV Medications¹

Web Site and Link

Notes

HIV Drug Interactions

University of Liverpool

http://www.hiv-druginteractions.org/

• Intuitive interaction checker that groups interactions by severity using colored headers
• Has a smart phone app

HIV InSite

University of California, San Francisco

http://arv.ucsf.edu/insite?page=ar-00-02

• Offers 3 ways to search for interactions: by antiretroviral drug, by interacting drug, or by interacting drug class

AIDSinfo

U.S. Department of health and Human Services

https://aidsinfo.nih.gov/

• Contains comprehensive charts for each antiviral class

Again, Aeschlimann suggests that pharmacists commit the most common drug interactions to memory, and stresses that pharmacists who initiate discussion about over-the-counter and complementary/alternative medications increase the margin of safety for patients. Note that several OTC items and complementary/alternative medications appear in the table above. Additionally, he advises increased vigilance as patients navigate transitions of care. Often, clinicians introduce error accidentally at these times and although the detective work takes a little bit of time, it's well worth it to ensure that the patient's medication regimen is correct.

So here's the "how-to": Establish relationships with your HIV-positive patients when they visit the pharmacy. Every visit doesn't have to be a comprehensive counseling session, but simply initiating conversation, asking how the patient is, and asking if anything is changed recently can open the door to information exchange. And a quick, "By the way, do you take any over-the-counter medication or supplements?" may provide information of great value.

References

• AIDS Education & Training Center Program, National Coordinating Resource Center. Drug-Drug Interactions with HIV-Related medications. Available at https://aidsetc.org/guide/drug-drug-interactions-hiv-related-medications. Accessed May 27, 2017.
• Panel on Antiretroviral Guidelines for Adults and Adolescents. Guidelines for the use of antiretroviral agents in HIV-1-infected adults and adolescents. Department of Health and Human Services. Available at http://aidsinfo.nih.gov/contentfiles/lvguidelines/AdultandAdolescentGL.pdf. Accessed May 27, 2017.