11.2 Viruses and Antiviral Drugs

Hepatitis Antivirals

Hepatitis viruses are clinically important because they can cause inflammation and damage to the liver. The three main types are hepatitis A virus (HAV), hepatitis B virus (HBV), and hepatitis C virus (HCV). HAV infection is usually self-limited, with many individuals being able to rid themselves of it without any intervention. HBV and HCV infections are of more clinical concern because without intervention, many clients will develop chronic infection, which can lead to cirrhosis, liver failure, and risk for liver cancer. HAV is spread via the fecal–oral route, and HBV and HCV are usually spread through parenteral transmission (such as by sharing contaminated needles) and during sexual intercourse. Vaccines can prevent HAV and HBV infections.

Medications to treat chronic HBV infection are not always curative and are used with the goal of preventing complications such as cirrhosis and liver cancer. HBV infection is typically managed with nucleoside/nucleotide antivirals, which include entecavir, tenofovir, lamivudine, adefovir, and telbivudine. These drugs work against viral DNA polymerase, an enzyme critical for DNA production and viral replication. They are incorporated into the viral DNA and function as “chain terminators,” meaning that no other nucleotides may be added onto them in the chain of DNA, and DNA production is thereby halted. Another treatment option is interferon (interferon alfa); however, due to toxicity, this medication is considered a last resort when all else fails.

HCV infection previously was a chronic disease with no definitive cure and consisted of treatment with parenteral medications with poor tolerability (e.g., interferons). This condition has radically changed, and now many clients with HCV can achieve virologic cure (no presence of the virus in the body) with 12–24 weeks of oral drug therapy using a direct-acting antiviral (DAA) agent such as sofosbuvir. The DAAs can work on a variety of steps in the HCV life cycle to prevent replication or transmission of active virus. Nurses should stress to clients that they must take the entire course of their DAA regimen because resistance can develop if the virus is not completely suppressed. More resistant cases may require treatment with the injectable drug ribavirin, the action of which is not currently understood.

Herpes Antivirals

Two main types of herpes viruses are responsible for causing clinically significant disease. Herpes simplex virus (HSV)-1 is usually responsible for causing lesions (e.g., cold sores) on the mouth, face, and skin. HSV-2 is usually responsible for infections in the genitals and rectum. No curative therapy for HSV-1 or HSV-2 currently exists, but medication is useful to reduce the duration and severity of symptoms a client experiences and to help prevent spread of the virus to other individuals. Agents used to treat herpes viruses include acyclovir and its oral prodrug, valacyclovir, as well as famciclovir. Ganciclovir, valganciclovir, and cidofovir also have activity against herpes viruses, but due to multiple adverse effects, they are reserved for cases of resistance to the first-line agents. These agents work by inhibiting the formation of new viral DNA by acting as chain terminators.

Clients with herpes virus infections may take these medications either when symptoms occur (episodic therapy) or every day for chronic suppression. Chronic suppression is linked to lower incidence of transmission of the virus to uninfected individuals and is useful for clients who have multiple outbreaks each year. Clients using the episodic method must be instructed to begin taking their therapy within 24 hours of symptom onset for the medication to be effective. They should also be informed that viral shedding can occur even without an active lesion, which may increase transmission risk.

Influenza Antivirals

Influenza refers to a diverse set of viruses known to cause upper respiratory tract illnesses, most commonly in the winter months. Annual vaccination will not prevent all infections but may help reduce the symptoms that individuals experience, and it is critical for protecting people most at risk for complications, such as older adults and immunocompromised individuals. However, vaccines are able to protect against only four strains each year with the current quadrivalent vaccines, which protect against two strains of influenza A and two of influenza B. This means that many people still go on to develop influenza infections that require treatment with medications.

The primary class of drugs used to treat influenza infection includes the neuraminidase inhibitors oseltamivir, zanamivir, and peramivir. Neuraminidase inhibitors work by inhibiting the enzyme neuraminidase, which is used to cleave mature copies of the virus from an infected cell to allow it to go infect other cells. Inhibiting this enzyme prohibits the virus from infecting host cells. If the client has had flulike symptoms for more than 48 hours, neuraminidase inhibitors should not be used due to lack of efficacy.

Oseltamivir is considered the first-line option for treatment of influenza and is given orally over 5 days. Zanamivir is an inhaled neuraminidase inhibitor that can be used as an alternative to oral oseltamivir. Peramivir is the only intravenous neuraminidase inhibitor and should be reserved for clients who cannot take oral or inhaled medications.

Table 7.3 lists common antivirals and typical routes and dosing for adult and pediatric clients.

Adverse Effects and Contraindications

Antiviral agents are known to cause gastrointestinal discomfort, including nausea, vomiting, and diarrhea. A contraindication to any antiviral drug is known hypersensitivity.

The nucleoside/nucleotide analogs used to treat HBV infection are considered safer than interferon products, but individual agents may be linked to serious complications such as entecavir-induced lactic acidosis and adefovir-induced nephrotoxicity.

Side effects of herpes antivirals are mild but can include blood cell production suppression, malaise, and risk for renal injury.

Zanamivir is given via inhalation and should not be used in clients with a history of asthma or chronic obstructive pulmonary disease due to risk for bronchospasm (tightening of the airways).

Table 7.4 is a drug prototype table for antivirals featuring acyclovir. It lists drug class, mechanism of action, adult and pediatric dosage, indications, therapeutic effects, drug and food interactions, adverse effects, and contraindications.

Nursing Implications

The nurse should do the following for clients who are taking antivirals:

• Monitor for signs and symptoms of anaphylaxis (e.g., shortness of breath, difficulty breathing, difficulty swallowing).
• Advise the client to take the entire prescribed course of the medication to ensure adequate treatment and to reduce the development of drug resistance.
• Instruct the client to maintain adequate hydration; monitor kidney function for renally eliminated antivirals such as acyclovir and valacyclovir.
• Monitor the client’s complete blood count to check for bone marrow suppression.
• Monitor for mental status changes in clients receiving intravenous antivirals who have poor renal function.
• For clients using antiviral medication episodically, teach them to begin taking it as soon as possible after symptom onset.
• Use appropriate personal protective equipment (e.g., mask and gloves) when clients are diagnosed with influenza to prevent infection spread.
• Check a pregnancy test in clients capable of pregnancy prior to initiating antiviral therapy.
• Provide client teaching regarding the drug and when to call the health care provider. See below for client teaching guidelines.