3.5: Antivirals

Unlike the complex structure of fungi or protozoa, viral structure is simple. There are several subclasses of antiviral medications: antiherpes, antiinfluenza, anti-hepatitis, and antiretrovirals. Each subclass will be discussed in more detail below. See Figure 3.10^[1] for images of viruses.

Figure 3.10 Images of viruses (a) Members of the Coronavirus family can cause respiratory infections like the common cold, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS). Here they are viewed under a transmission electron microscope (TEM). (b) Ebolavirus, a member of the Filovirus family. (credit a: modification of work by Centers for Disease Control and Prevention; credit b: modification of work by Thomas W. Geisbert)

Subclass: Antiherpes

Indications: Acyclovir (Zovirax) and its derivatives are frequently used for the treatment of herpes and varicella virus infections, including genital herpes, chickenpox, shingles, Epstein-Barr virus infections, and cytomegalovirus infections.

Mechanism of Action: Acyclovir causes termination of the DNA chain during the viral replication process. Acyclovir can be administered either topically or systemically, depending on the infection.^[2]

Special Administration Considerations: Acyclovir use may result in nephrotoxicity.

Patient Teaching & Education: Patients who are being treated with antiviral therapy should be instructed about the importance of medication compliance. They may also experience significant fatigue, so periods of rest should be encouraged.^[3]

Subclass: AntiInfluenza

Indications: Tamiflu (oseltamivir) is used to target the influenza virus by blocking the release of the virus from the infected cells.

Mechanism of Action: Tamiflu prevents the release of virus from infected cells.

Special Administration Considerations: This medication does not cure influenza, but can decrease flu symptoms and shorten the duration of illness if taken in a timely manner. Patients are prescribed the medication for prophylaxis against infection, known exposure, or to lesson the course of the illness. If patients experience flu-like symptoms, it is critical that they start treatment within 48 hours of symptom onset.

Patient Teaching & Education: Patients who are being treated with antiviral therapy should be instructed about the importance of medication compliance. They may also experience significant fatigue, so periods of rest should be encouraged.^[4]

The influenza virus is one of the few RNA viruses that replicates in the nucleus of cells. Antivirals block the release stage. See Figure 3.11.^[5]

Figure 3.11 Influenza virus replication stages

Subclass: Antiretrovirals

Viruses with complex life cycles, such as HIV, can be more difficult to treat. These types of viruses require the use of antiretroviral medications that block viral replication. (See Figure 3.12 to view the viral replication process of HIV.)^[6] Additionally, antiretrovirals fall under the class of antiviral medications.

Figure 3.12 HIV attaches to a cell surface receptor of an immune cell and fuses with the cell membrane. Viral contents are released into the cell, where viral enzymes convert the single-stranded RNA genome into DNA and incorporate it into the host genome

Indications: Antiretrovirals are used for the treatment of illnesses like HIV.

Mechanism of Action: Antiretrovirals impede virus replication.

Special Administration Considerations: Many antiretrovirals may impact renal function; therefore, the patient’s urine output and renal labs should be monitored carefully for signs of decreased function.

Patient Teaching & Education: Patients who are being treated with antiviral therapy should be instructed about the importance of antiretroviral compliance. They may also experience significant fatigue, so periods of rest should be encouraged.^[7]

Now let’s take a closer look at the medication grids for the subclasses of antivirals in Table 3.14a-d.^[8]

Tables 3.14a Acyclovir Medication Grid

Class/Subclass	Prototype/ Generic	Administration Considerations	Therapeutic Effects	Side/Adverse Effects
Antivirals: Antiherpes	acyclovir	Check for allergies Route: PO, IV, or topical; do not give IM or subcutaneously (subq) Give with food if GI distress IV: Give IV infusion over at least 1 hour to prevent renal tubular damage Use cautiously if renal impairment, neurological problems, or dehydration Start therapy as early as possible after signs or symptoms occur Encourage fluid intake Avoid sexual contact while lesions present	Drug is not a cure for herpes but improves signs and symptoms of herpes lesions if started early Can be used long term for prevention of outbreaks	GI distress Monitor renal function in long-term use, especially if renal impairment Lowers seizure threshold

Tables 3.14b Oseltamivir Medication Grid

Class/Subclass	Prototype/ Generic	Administration Considerations	Therapeutic Effects	Side/Adverse Effects
Antivirals: AntiInfluenza Agents	oseltamivir	Check for allergies Route: PO Must be given within 48 hours of onset of symptoms Administer with food to avoid GI distress Does not replace need for annual influenza vaccination	Reduce duration of flu symptoms	GI distress Serious skin/ hypersensitivity reactions; discontinue immediately Monitor for neuropsychiatric symptoms Use cautiously in patients with renal failure, chronic cardiac or respiratory diseases, or any medical condition that may require imminent hospitalization

Tables 3.14c Adefovir Medication Grid

Class/Subclass	Prototype/ Generic	Administration Considerations	Therapeutic Effects	Side/Adverse Effects
Antivirals: Anti-Hepatitis Agents	adefovir	Route: PO Prolonged therapy (>1 year or indefinitely) based on patient status Offer HIV testing; may promote resistance to antiretrovirals in patients with chronic HBV infection who also have unrecognized or untreated HIV infection Do not stop taking medication unless directed. Monitor hepatic function several months after stopping therapy	Maintain or improve liver function when active disease is present	Severe acute exacerbations of Hepatitis B Nephrotoxicity Lactic acidosis Severe hepatomegally

Tables 3.14d Lamuvadine-Zidovudine Medication Grid

Class/Subclass	Prototype/ Generic	Administration Considerations	Therapeutic Effects	Side/Adverse Effects
Antivirals: Antiretrovirals Nucleoside– nucleotide reverse transcriptase inhibitors	lamivudine- zidovudine	Check for allergies Lamivudine used to treat HIV-1 infection contains a higher dose of the active ingredient than the lamivudine used to treat chronic HBV infection. Patients with HIV-1 infection should receive only dosing forms appropriate for HIV-1 treatment Use cautiously in patients with renal impairment Inform patient that drug doesn’t cure HIV infection, that opportunistic infections and other complications of HIV infection may still occur, and that transmission of HIV to others through sexual contact or blood contamination is still possible. Taking these medications, along with practicing safer sex and making other lifestyle changes, may decrease the risk of transmitting (spreading) the HIV or hepatitis B virus to other people Teach symptoms of pancreatitis	Decreases chance of developing acquired immunodeficiency syndrome (AIDS) and HIV-related illnesses such as serious infections or cancer	Lactic acidosis Severe hepatomegaly Stop treatment immediately if pancreatititis

Critical Thinking Activity 3.14a

Using the above grid information, consider the following clinical scenario question:

A patient is prescribed oseltamivir (Tamiflu) for influenza symptoms. The patient states to the nurse, “I hope this medication works quickly! I have felt lousy for the past 5 days!” What is the nurse’s next best response?

Note: Answers to the Critical Thinking activities can be found in the “Answer Key” sections at the end of the book.

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1. "Unknown" by CNX OpenStax is licensed under CC BY 4.0 Access for free at https://openstax.org/books/microbiology/pages/1-3-types-of-microorganisms↵
2. This work is a derivative of Microbiology by OpenStax licensed under CC BY 4.0. Access for free at https://openstax.org/books/microbiology/pages/1-introduction↵
3. uCentral from Unbound Medicine. https://www.unboundmedicine.com/ucentral↵
4. uCentral from Unbound Medicine. https://www.unboundmedicine.com/ucentral↵
5. "Unknown" by CNX OpenStax is licensed under CC BY 4.0 Access for free at https://openstax.org/books/microbiology/pages/6-2-the-viral-life-cycle↵
6. This work is a derivative of "HIV Virus Replication Cycle" by NIAID is licensed under CC BY 2.0↵
7. uCentral from Unbound Medicine. https://www.unboundmedicine.com/ucentral↵
8. Daily Med, dailymed.nlm.nih.gov/dailymed/index.cfm, used for hyperlinked medications in this module. Retrieved June 27, 2019 ↵