NAPLEX Question of the Week: Viral Respiratory Tract Infections

This week's question focuses on a common respiratory virus.
NAPLEX Question of the Week: Viral Respiratory Tract Infections

CG is a 62 year old male (5'10", 200 lbs) who presents to his primary care physician with a one day history of fever (100.9 F in office), chills, body aches, and dry hacking cough. His past medical history is significant for asthma, hypertension, GERD, and hyperlipidemia. He currently confirms taking lisinopril/hctz 40/12.5mg daily, Flovent 110mcg 2 puffs daily, omeprazole 20mg once daily, and atorvastatin 40mg once daily. His allergies include lactose (hives) and sulfa (hives). Rapid PCR diagnostic testing reveals the following:

Influenza A: Negative

Influenza B: Positive

SARS-CoV-2: Negative

His vital signs are stable. CBC and Chem-7 are pending. His Chem-7 from two months prior was within normal limits. 

Which of the following regimens would be appropriate to treat CG assuming his renal function returns normal? Select all that apply. 

A. Oseltamivir 150mg PO BID for 5 days

B. Baloxavir 80mg PO X 1 dose

C. Peramivir 600mg IV X 1 dose over 15-30 minutes

D. Zanamivir 10mg PO BID for 5 days

E. Molnupiravir 800mg PO BID for 5 days

Brand/generics covered: Oseltamivir (Tamiflu), Baloxavir (Xofluza), Peramivir (Rapivab), Zanamavir (Relenza), Molnupiravir (Lagevrio)

Answers with Rationale:

The correct answers are B and C.

Pharmacists are becoming more and more involved with not only the treatment of influenza but also the diagnosis, with rapid diagnostic test availability providing a more rapid option for detecting disease. The COVID-19 pandemic has sped up these processes to aid patient's receiving effective antiviral therapy as quickly as possible.

In this case, the patient was tested by their primary care physician for both COVID-19 and influenza (A and B) with the influenza B positive. Signs/symptoms of these two viruses overlap significantly so testing for both is prudent. In addition, there are rapid diagnostic viral respiratory panels on the market that can test for a number of different viruses and bacteria that aid in detection of the offending pathogen. Ideally antiviral therapy should be started within 48 hours of symptom onset although some situations exist (typically severe disease manifested by hospitalization) when therapy may be initiated after 48 hours. Our patient is within the 48 hour mark but let's see why some of the answers were incorrect. 

Answer A is incorrect as this is the incorrect dose for Tamiflu. While Tamiflu would be a go to option here, the correct dose is 75mg PO BID for 5 days. 

Answer B is correct. Baloxivir is a newer, one dose option for the treatment of influenza. It is a weight based dose with patients 20kg to < 80kg receiving 40mg X 1 dose with patients 80kg or more receiving 80mg PO X 1 dose. Our patient is 200 pounds so this equates to ~91kg which would make the 80kg dose correct.  In addition, similar to fluoroquinolones, multivalent cations can chelate the compound rendering it less effective. Therefore these should not be co-administered together.

Answer C is correct. While not used often due to the IV dosage form, it is FDA-approved for acute treatment. In a patient with severe nausea/vomiting this would provide an IV option.

Answer D is incorrect. Zanamivir is an inhaled option for the management of influenza. Our patient has a known allergy to lactose which is a contraindication for zanamivir therapy. Caution should also be given to any patient with known lung disease (e.g. asthma, COPD) due to the potential for bronchospasm upon administration. Our patient has asthma and thus would not be ideal candidate. In addition, the route of administration is oral but should be inhaled which is important to keep in mind. 

Answer E is incorrect. Molnupiravir is a treatment for COVID-19, not influenza. It is not a first-line therapy for mild-moderate COVID-19 due to less efficacy vs. other oral agents, such as Paxlovid. 

Be sure and review pediatric dosages and prophylaxis doses for these agents when applicable as these are common in clinical practice as well. 

Be sure and look over the first two posts of the year if you did not so you have a good plan for 2023 to be successful on the NAPLEX. See everyone next week!

Dr. B

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