Antiviral agents

Last updated: March 6, 2023

Summarytoggle arrow icon

Antivirals are a class of medications that are used to treat viral infections. Most viral infections resolve spontaneously in immunocompetent individuals. The aim of antiviral therapy is to minimize symptoms and infectivity as well as to shorten the duration of illness. These drugs act by arresting the viral replication cycle at various stages. Currently, antiviral therapy is available only for a limited number of infections. Most of the antiviral drugs currently available are used to treat infections caused by HIV, herpes viruses, hepatitis B and C viruses, and influenza A and B viruses. Because viruses are obligate intracellular parasites, it is difficult to find drug targets that interfere with viral replication without also harming the host cells. Unlike other antimicrobials, antiviral drugs do not deactivate or destroy the microbe (in this case, the virus) but act by inhibiting replication. In this way, they prevent the viral load from increasing to a point where it could cause pathogenesis, allowing the body's innate immune mechanisms to neutralize the virus. This article provides an overview of the most commonly used antiviral agents. For more information on antiretroviral agents used in the treatment of HIV, which is known as highly active antiretroviral therapy (HAART), see “Overview of antiretrovirals for HIV treatment.”

Overviewtoggle arrow icon

Viruses are obligate pathogens, which depend on host-cell machinery for replication. Most antiviral agents target key enzymes required for viral replication (see “Viral life cycle for details).

Overview of the viral replication cycle and targets of antiviral drug
Viral replication cycle Target Antiviral drug
Fusion with host cell
  • Attachment
  • Penetration
Replication of viral genome
Protein synthesis and assembly of viral components
Release of new viruses from host cell

Antivirals against hepatitis B and Ctoggle arrow icon

See “Antiviral treatment of chronic hepatitis C” and “Antiviral treatment of chronic hepatitis B.”

Antivirals against both hepatitis B and C

Overview of antivirals against both hepatitis B and C [1][2]
Agents Mechanism of action Indications Contraindications Adverse effects

Pegylated interferon alfa and interferon-α

  • Antiviral and immunomodulatory effect via intercellular and intracellular mechanisms

Antivirals against hepatitis B

Overview of antivirals against hepatitis B [2]
Agents Mechanism of action Indications Adverse effects






Antivirals against hepatitis C

Overview of antivirals against hepatitis C [1]
Agents Mechanism of action Indications Adverse effects
Direct acting antivirals (DAAs)


  • NS3/4A protease inhibitors
  • Inhibition of NS3/4A (an HCV serine protease required for viral replication) → ↓ viral replication





  • Non-nucleoside NS5A polymerase inhibitors
  • Exact mechanism of action is unknown
  • Inhibition of the viral NS5A phosphoprotein, which is essential for replication → prevention of HCV RNA replication








Protease inhibitors used to treat HIV end in ”navir.” Protease inhibitors used to treat HCV end in “previr.”

Antivirals against herpes virusestoggle arrow icon

Overview of antivirals against herpesviruses [3][4][5]
Agents Mechanism of action Indications Adverse effects Mechanism of antiviral resistance







  • Systemic treatment of choice for CMV retinitis in immunocompromised patients (e.g., patients with AIDS)
  • CMV prophylaxis in transplant recipients
  • Mutation of viral UL97 kinase


  • Unknown

Antivirals against influenza virusestoggle arrow icon

Overview of antivirals against influenza viruses [6][7][8]


Mechanism of action Indications

Adverse effects






  • Neuraminidase inhibitor: inhibition of progeny release from the surface of infected host cells
  • Treatment of influenza A and B (reduces symptom duration if taken within 1–2 days of symptom onset)
  • Prophylaxis of influenza in adults and pediatric patients ≥1 year (oseltamivir) and ≥ 5 years (zanamivir) of age
Baloxavir marboxil
  • Treatment of influenza A and B (reduces symptom duration if taken within 48 hours of symptom onset)

In influenza A and B, administration of neuraminidase inhibitors within 2 days of symptom onset is vital to reduce the duration of illness and alleviate symptoms.

Referencestoggle arrow icon

  1. Lanier ER, Foster S, Brundage T, et al. Analysis of mutations in the gene encoding cytomegalovirus DNA polymerase in a phase 2 clinical trial of brincidofovir prophylaxis. J Infect Dis. 2016; 214 (1): p.32-35.doi: 10.1093/infdis/jiw073 . | Open in Read by QxMD
  2. Prichard MN. Function of human cytomegalovirus UL97 kinase in viral infection and its inhibition by maribavir. Rev Med Virol. 2009; 19 (4): p.215-229.doi: 10.1002/rmv.615 . | Open in Read by QxMD
  3. He Z, He YS, Kim Y, et al. The human cytomegalovirus UL97 protein is a protein kinase that autophosphorylates on serines and threonines.. J Virol. 1997; 71 (1): p.405-11.
  4. HCV Guidance: Recommendations for Testing, Managing, and Treating Hepatitis C. Updated: August 27, 2020. Accessed: December 3, 2020.
  5. Katzung B,Trevor A. Basic and Clinical Pharmacology. McGraw-Hill Education ; 2014
  6. UpToDate. Rimantadine: Drug information. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. . Accessed: February 21, 2017.
  7. Zanamivir. . Accessed: February 21, 2017.
  8. Stiver G. The treatment of influenza with antiviral drugs. CMAJ. 2003; 168 (1): p.49-57.

Icon of a lock3 free articles remaining

You have 3 free member-only articles left this month. Sign up and get unlimited access.
 Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer