NAPLEX Question of the Week: Antiviral Medication Mechanism of Action

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Which of the following antiviral medications correctly matches its mechanism of action?

A. Emtricitabine – nucleoside reverse transcriptase inhibitor

B. Darunavir – non-nucleoside reverse transcriptase inhibitor

C. Abacavir – integrase strand transfer inhibitor

D. Bictegravir – protease inhibitor


Answer with rationale:

The correct answer is A.

Mechanisms of action are important for pharmacists to know, and this question aligns with NAPLEX Competency Statement 1.2.5: Actions and mechanisms of actions of drugs. Antiviral medications can be tricky as many sound very similar, so this area may take some additional time to review when studying for the NAPLEX.

A is correct. Emtricitabine (Emtriva) is a nucleoside reverse transcriptase inhibitor (NRTI) and is used in the treatment of HIV. It is also a component in Truvada (emtricitabine and tenofovir disoproxil fumarate) and Descovy (emtricitabine and tenofovir alafenamide), both of which are approved for pre-exposure prophylaxis (PrEP). Adverse drug reactions include hyperpigmentation of palms/soles, nails, or lips, insomnia, and dizziness. Emtricitabine has a black box warning for acute exacerbation of hepatitis B upon discontinuation, so liver function should be monitored closely for several months in patients after discontinuation.

B is incorrect. Darunavir (Prezista) is a protease inhibitor. It also comes in combination tablets Prezcobiz (darunavir and cobicistat) and Symtuza (darunavir, cobicistat, emtricitabine, and tenofovir alafenamide). One thing to note is that darunavir contains a sulfonamide moiety and should be avoided in patients with a sulfa allergy. Some adverse drug reactions of darunavir include fat redistribution, hepatotoxicity, and hypercholesterolemia.

C is incorrect. Abacavir (Ziagen) is an NRTI. It is also a component in Epzicom (abacavir and lamivudine), Trizivir (abacavir, lamivudine, and zidovudine), and Triumeq (abacavir, lamivudine, and dolutegravir). All patients should be screened for the HLA-B*5701 allele prior to initiating therapy with abacavir due to risk of serious and sometimes fatal hypersensitivity reactions. Should such a hypersensitivity reaction occur, abacavir or any abacavir-containing product should never be used again because more severe symptoms including death, can occur within hours of re-initiation. Abacavir is generally well tolerated, but some adverse drug reactions include fatigue, sleep disorders, anxiety, and nausea.

D is incorrect. Bictegravir is an integrase strand transfer inhibitor (INSTI). It is only available in the combination tablet by the name of Biktarvy (bictegravir, emtricitabine, and tenofovir alafenamide). Two important drug interactions to know with bictegravir are metformin and polyvalent cations (i.e. iron, calcium, magnesium, etc.). Bictegravir is an inhibitor of the transporters OCT2 and MATE1, which are involved in the elimination of metformin. Therefore, bictegravir can increase concentrations of metformin. Additionally, chelation of polyvalent cations may occur with Biktarvy and decrease drug concentrations. Administration should be separated by 2 hours before or 6 hours after aluminum- or magnesium-containing antacids. Biktarvy can be taken with concomitant calcium- or iron-containing supplements or antacids if taken together with food. However, concomitant administration of Biktarvy with calcium- or iron-containing supplements or antacids is not recommended in a fasting state. Adverse reactions of Biktarvy include hyperbilirubinemia, increased creatine kinase, and diarrhea.

Have a great week everyone!

Dr. B

Christopher M. Bland

Clinical Professor, University of Georgia College of Pharmacy

Dr. Christopher M. Bland is a Clinical Professor at the University of Georgia College of Pharmacy at the Southeast GA campus in Savannah, GA. Dr. Bland has over 20 years of academic and clinical experience in a number of clinical areas. He is a Fellow of both the Infectious Diseases Society of America as well as the American College of Clinical Pharmacy. He is co-founder of the Southeastern Research Group Endeavor, SERGE-45, with over 80 practitioners across 14 states involved. Dr. Bland serves as Associate Editor for the NAPLEX Review Guide 4th edition as well as Editor-In-Chief for the Question of the Week. He has provided live, interactive reviews for more than 10 Colleges/Schools of Pharmacy over the course of his career.