How Do Other Antivirals Work?

Antivirals are medications used in the treatment and prevention of various types of viral infections. Other antivirals are medications that are not categorized into any specific classes of antivirals. Most of the other antivirals block viral replication by interfering with DNA polymerase, an enzyme vital for DNA synthesis and viral replication.

Some of the other antivirals are active drugs that directly take effect, while some are prodrugs, which release the active form of the drug after being metabolized. Other antivirals include the following:

• Acyclovir: Acyclovir is an active drug effective against herpes simplex virus 1 and 2 (HSV-1 and HSV-2) that cause genital and oral herpes, and varicella-zoster virus (VZV) which causes chickenpox and shingles. Acyclovir gets incorporated into the viral DNA, inhibits DNA polymerase, and terminates the DNA chain to prevent viral replication.
• Brincidofovir: Brincidofovir is a prodrug approved for treating human smallpox, a disease caused by the variola virus. Although smallpox has been eradicated with vaccination, concerns that the variola virus can be used as a bioweapon remain.
  • Brincidofovir penetrates cells and releases cidofovir which is metabolized to produce cidofovir diphosphate, the active drug that selectively inhibits orthopoxvirus DNA polymerase-mediated viral DNA synthesis and reduces the rate of viral DNA synthesis.
• Famciclovir: Famciclovir is a prodrug of penciclovir and is used to treat shingles, and suppress recurrent episodes of HSV-1 and HSV-2 in immunocompetent adults as well as human immunodeficiency virus (HIV)-infected adults. Famciclovir blocks viral replication by inhibiting viral DNA polymerase.
• Foscarnet: Foscarnet (phosphonoformic acid) is used to treat cytomegalovirus (CMV) infection and HSV in immunocompromised adults with resistance to acyclovir. Foscarnet works by inhibiting the activity of the pyrophosphate binding site on viral DNA polymerase and prevents viral replication.
• Remdesivir: Remdesivir is used to treat COVID-19, caused by SARS-CoV-2, an RNA virus. Remdesivir is a prodrug that is metabolized into remdesivir triphosphate (RDV-TP), which inhibits SARS-CoV-2 RNA-dependent RNA polymerase, the enzyme essential for viral replication.
• Tecovirimat: Tecovirimat is an antiviral drug approved for the treatment of human smallpox disease. Tecovirimat inhibits the activity of orthopoxvirus VP37 protein, preventing the formation of enveloped viral particles (virions) which can get out of the infected cells and infect other healthy cells.
• Valacyclovir: Valacyclovir is a prodrug and is metabolized by the liver into acyclovir and has similar effects against HSV infections.
• Valganciclovir: Valganciclovir is a prodrug of ganciclovir, used in the prevention and treatment of CMV infection. Valganciclovir inhibits viral DNA polymerase and prevents DNA synthesis and chain elongation. The drug gets incorporated into the viral DNA and prevents the incorporation of deoxyguanosine triphosphate, an essential compound required for DNA synthesis.

Other antivirals may be administered through the following routes:

• Oral tablets, capsules, solutions, or suspensions
• Intravenous (IV) infusions
• Intravenous injections

The FDA-approved uses of other antivirals include:

• Acyclovir:
  • Treatment and suppression of genital herpes
  • Herpes simplex virus (HSV) encephalitis (brain inflammation)
  • Treatment of mucocutaneous HSV infection in immunocompromised adults
  • Neonatal HSV infection
  • Varicella-zoster infection (chickenpox)
  • Herpes zoster infection (shingles), which is caused by reactivation of VZV
  • Herpetic keratitis (corneal inflammation from herpes) - Orphan
• Brincidofovir:
  • Human smallpox disease, caused by the variola virus
• Famciclovir:
  • Acute herpes zoster infection (shingles)
  • Herpes labialis (cold sores that primarily affect the lips)
  • Genital herpes
  • Prevention of HSV reactivation and treatment of recurrent episodes in adults infected with human immunodeficiency virus (HIV)
• Foscarnet:
  • Cytomegalovirus (CMV) retinitis (inflammation of the retina) in adults with acquired immunodeficiency syndrome (AIDS)
  • HSV in immunocompromised adults with resistance to acyclovir
  • Remdesivir:
  • Treatment of coronavirus disease 2019 (COVID-19) in hospitalized patients aged 12 years or older
• Tecovirimat:
  • Human smallpox disease
• Valacyclovir:
  • Herpes labialis
  • Herpes zoster
  • Genital herpes
  • Chickenpox
• Valganciclovir:
  • Treatment of CMV retinitis in adults with AIDS
  • CMV prevention in solid organ (heart/kidney/pancreas) transplant
  • CMV colitis or esophagitis in HIV-infected adults (off-label)
  • Lymphoproliferative disorder (orphan designation)

Side effects of other antivirals vary with each type of drug. A few of the most common side effects may include:

• Acyclovir:
  • Malaise
  • Inflammation or phlebitis (vein inflammation) at the injection site
  • Nausea and vomiting
  • Diarrhea
  • Rash or hives
  • Headache
• Brincidofovir:
  • Diarrhea
  • Nausea and vomiting
  • Abdominal pain
  • Elevated serum creatinine
  • Elevated liver enzymes ALT and AST
  • Elevated total bilirubin
• Famciclovir:
  • Headache
  • Nausea and vomiting
  • Abdominal pain
  • Dysmenorrhea (painful menstruation)
  • Flatulence
  • Rash and pruritus (itching)
• Foscarnet:
  • Fever and headache
  • Nausea and vomiting
  • Anemia
  • Diarrhea
  • Abnormal kidney function
  • Seizures
• Remdesivir:
  • Abnormal kidney function with reduced eGFR and elevated creatinine level
  • Decrease in hemoglobin
  • Increase in blood glucose levels
  • Decrease in lymphocytes
  • Increase in prothrombin time (blood clotting time)
  • An increase in liver enzymes ALT and AST
• Tecovirimat:
  • Headache
  • Nausea and vomiting
  • Abdominal pain
  • Dry mouth and oropharyngeal pain
  • Skin and subcutaneous reactions
  • Abnormal electroencephalogram (EEG)
• Valacyclovir:
  • Headache
  • Neutropenia (low neutrophil count in the blood)
  • Elevated liver enzymes ALT and AST
  • Nasopharyngitis (inflammation of nose and throat)
  • Nausea
  • Abdominal pain
• Valganciclovir:
  • Diarrhea and abdominal pain
  • Anemia and granulocytopenia (low count of granulocytes, type of immune cells)
  • Fever and headache
  • Insomnia
  • Nausea and vomiting
  • Retinal detachment

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of some of the other antivirals include:

• acyclovir
• brincidofovir
• famciclovir
• Famvir
• foscarnet
• Foscavir
• Phosphonoformic acid
• remdesivir
• tecovirimat
• Tembexa
• TPOXX
• valacyclovir
• Valcyte
• valganciclovir
• Valtrex
• Veklury
• Zovirax