Antiviral drug types
Antiviral drugs are specialized medications designed to combat viral infections by preventing the replication of viruses within human cells. These drugs are categorized based on the specific virus they target, such as influenza, HIV, hepatitis, and herpes, or by their functional mechanisms. Common classifications include nucleoside reverse transcriptase inhibitors (NRTIs), protease inhibitors, and neuraminidase inhibitors, among others. Antivirals can be administered in various forms, including tablets, eye drops, inhaled powders, and injections.
For example, the treatment of HIV involves several subclasses of antivirals that target different viral components, such as enzymes necessary for replication. In contrast, antiviral treatments for influenza focus on disrupting the virus's entry into host cells or its ability to replicate. Additionally, there are effective medications for herpesvirus infections, which inhibit viral DNA synthesis. The range of antiviral options available is vital for addressing diverse viral diseases, and understanding their mechanisms is essential for proper treatment.
Antiviral drug types
Definition
Antiviral drugs are medications used to prevent the replication of viruses in the cells of the human body during infection. They are classified by the type of virus they target, like influenza, HIV, hepatitis, and herpes, or by their function, such as nucleoside reverse transcriptase inhibitors, fusion inhibitors, protease inhibitors, nonnucleoside reverse transcriptase inhibitors, or integrase inhibitors. These drugs are available in eye drops, inhaled powders, IV infusions, injections, and topical creams.
HIV and AIDS Medications
Antivirals targeted at the human immunodeficiency virus (HIV) make up more than one-half of the available antivirals. These antivirals can be divided into six subclasses: nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), integrase strand transfer inhibitors (INSTIs), CCR5 antagonists, and fusion inhibitors. Each class targets a different HIV enzyme or receptor.
Nucleoside reverse transcriptase inhibitors. NRTIs are competitive substrate inhibitors that are complete with naturally occurring deoxynucleotides. NRTIs inhibit the enzyme reverse transcriptase, thereby blocking the transcription of viral ribonucleic acid (RNA) to host deoxyribonucleic acid (DNA), preventing HIV from replicating and preventing incorporation into the host genome. Available NRTIs include zidovudine (Retrovir), stavudine (Zerit), lamivudine (Epivir), abacavir (Ziagen), emtricitabine (Emtriva), and tenofovir (Vemlidy, Viread).
Non-nucleoside reverse transcriptase inhibitors. NNRTIs prevent viral RNA from being converted into DNA through the inhibition of reverse transcriptase. Available NNRTIs include efavirenz (Sustiva and Atripla), nevirapine (Viramune), delavirdine (Delstrigo and Pifeltro), rilpivirine (Cabenuva, Complera, Edurant, Juluca, and Odefsey) and etravirine (Intelence).
Protease inhibitors. HIV protease is an enzyme that exerts its effect after HIV has successfully entered the host cell and been incorporated into the host genome. Protease is responsible for breaking large protein strands called polyproteins into smaller viral particles, which then mature and become infectious to the host. Protease inhibitors prevent this cleaving of polyproteins and, therefore, prevent HIV particles from maturing and replicating. Available protease inhibitors include atazanavir, darunavir, fosamprenavir, indinavir, lopinavir/ritonavir, nelfinavir mesylate, ritonavir, saquinavir, and tipranavir.
Integrase strand transfer inhibitors. Integrase is an enzyme that facilitates the insertion of viral HIV DNA into the host cell DNA. By inhibiting the incorporation of the viral DNA, there is no formation of the provirus and, therefore, no viral reproduction within the host. Available ISTI medications include raltegravir (Isentress), elvitegravir (Vitekta), dolutegravir (Tivicay), bictegravir (Biktarvy), and cabotegravir (Vocabria).
CCR5 antagonists. CCR5, along with CXCR4, is an important coreceptor facilitating the entry of HIV into the host cells. CCR5 antagonists inhibit CCR5, changing the conformation of the coreceptor and, therefore, preventing fusion of the host cell membrane and HIV. Available CCR5 antagonists include maraviroc (Selzentry) and aplaviroc.
Fusion inhibitors. Fusion inhibitors, also called entry inhibitors, bind to the viral envelope glycoprotein and block the conformational change that, if carried out, would result in the fusion on the HIV viral and host cell membrane. Available fusion inhibitors include enfurvirtide (T-20), enfuvirtide (Fuzeon), and fostemsavir (Rukobia).
Influenza Medications
Four primary antiviral medications are available, either as treatment or prophylaxis, for influenza A or B. These drugs can be divided into M2 inhibitors and neuraminidase inhibitors. M2 inhibitors can be used prophylactically or for the treatment of influenza A; however, the U.S. Food and Drug Administration has issued statements that M2 inhibitors are not recommended for some flu strains. M2 inhibitors work by inhibiting the uncoating of the influenza A virus, thereby blocking the entrance of the virus into the host. Available M2 inhibitors include amantadine (Gocovri) and rimantadine (Flumadine).
Neuraminidase inhibitors are the drug of choice for current influenza strains and are active against both A and B strains. Both are approved for both prophylaxis and treatment. Neuraminidase enzyme is an enzyme that plays a role in preparing the glycoproteins to which the influenza virus can attach. Available neuraminidase inhibitors are zanamivir (Relenza) and oseltamivir phosphate (Tamiflu).
Other antiviral medications commonly used in patients with influenza include peramivir (Rapivab) and baloxavir marboxil (Xofluza).
Herpesvirus Medications
Another virus that can lead to a variety of symptoms and complications is the herpes simplex virus (HSV). HSV can be divided into two types, HSV-1 and HSV-2. Additional viruses within the herpes family include cytomegalovirus (CMV), Epstein-Barr virus (EBV), and varicella zoster virus (VZV). The herpesvirus can cause an array of infections affecting various body structures, including genital, orolabial, dermatologic, and ocular. Agents used to treat HSV-1 and HSV-2 include acyclovir, famiciclovir, and valacyclovir. Acyclovir and related agents work by inhibiting DNA polymerase, stopping viral DNA synthesis.
Hepatitis Medications
Treatment for hepatitis C includes a regimen of pegylated interferon alpha-2a (Pegasys ProClick, Pegasys) in combination with ribavirin (Moderiba, Virazole, Ribasphere), an antiviral. Ribavirin inhibits viral protein synthesis by preventing both replication of viral genome and elongation of RNA fragments. It is always used in combination with other drugs. For chronic hepatitis B virus infection, other antiviral medications include entecavir (Baraclude), tenofovir disoproxil fumarate (Viread), tenofovir alafenamide (Vemlidy), telbivudine (Tyzeka, Sebivo), and adefovir dipivoxil (Hepsera). For hepatitis C, antiviral medications include elbasvir/grazoprevir (Zepatier), glecaprevir/pibrentasvir (Mavyret), and sofosbuvir/velpatasvir (Epclusa).
Impact
The antivirals covered here represent some of the most commonly used antivirals. Viral diseases that respond to antiviral treatment include HIV and AIDS, influenza, HSV, and viral hepatitis. Mechanisms of action vary among agents, even those used to treat a specific virus. Clinicians must accurately differentiate between bacterial and viral pathology to correctly treat ailments that may have similar presentations.
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