Antibiotics part 4
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There are a few antiviral drugs that can be used to treat human viral infections, though they face challenges. Antiviral drugs must selectively inhibit the virus without harming human cells, as viruses hijack cell machinery. Possible targets for antiviral drugs include preventing viral absorption, intracellular penetration, and inhibiting protein or nucleic acid synthesis. Amantadine inhibits influenza A viral penetration but not other influenza types. Methisazone inhibits DNA viruses like vaccinia and variola used for smallpox prophylaxis. Interferons are proteins produced by infected cells that induce other proteins to inhibit viral mRNA transcription. There are type I and type II interferons that have different properties.
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Antibiotics part 4
- 2. • Several compounds are known that are inhibitory to mammalian viruses in tissue culture. • Only a few can be used in the treatment of human viral infections. • Lack of selective toxicity
- 3. • Viruses takes over the machinery of an infected human cell. • Antiviral drug must be remarkably selectively toxic • i.e.- inhibit the viral particle without adversely affecting the human cell.
- 4. • Comparison with antibacterial agents- • Very few inhibitors can be considered as being safe antiviral drugs. • Possible sites of attack by antiviral agents- • prevention of adsorption of a viral particle to the host cell • prevention of the intracellular penetration of the adsorbed virus • inhibition of protein or nucleic synthesis
- 5. Amantadines • Amantadine hydrochloride does not prevent adsorption but inhibits viral penetration. • It has a very narrow spectrum • Used prophylactically against infection with influenza A virus • Has no prophylactic value with other types of influenza virus. • he mechanism of amantadine's antiviral activity involves interference with the viral protein, M2, a proton channel.
- 6. Methisazone • Methisazone inhibits DNA viruses (particularly vaccinia and variola) but not RNA viruses. • Has been used in the prophylaxis of smallpox. It is now less used, especially as, according to the World Health Organization, smallpox has now been eradicated.
- 7. Interferons • Interferon is a low molecular weight protein • produced by virus-infected cells • Itself induces the formation of a second protein inhibiting the transcription of viral mRNA.
- 8. Type I interferons • These are acid-stable • Comprise two major classes, -leucocyte interferon (Le-IFN, IFN-a) released by stimulated leucocytes, -fibroblast interferon (F-IFN, IFN-/3) released by stimulated fibroblasts.
- 9. Type II interferons • These are acid-labile and are also known as 'immune' (IFN-y) interferons because they are produced by T-lymphocytes in the cellular immune system in response to specific antigens. Type I interferons induce a virus-resistant state in human cells, whereas Type II are more active in inhibiting growth of tumour cells.
Editor's Notes
- Like antibiotics and broad-spectrum antibiotics for bacteria, most antivirals are used for specific viral infections, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do not destroy their target pathogen; instead they inhibit their development. Most of the antiviral drugs now available are designed to help deal with HIV, herpes viruses, the hepatitis B and C viruses, and influenza A and B viruses. Researchers are working to extend the range of antivirals to other families of pathogens.
- Several compounds are known that are inhibitory to mammalian viruses in tissue culture, but only a few can be used in the treatment of human viral infections. The main problem in designing and developing antiviral agents is the lack of selective toxicity that is normally possessed by most compounds.
- Viruses literally 'take over' the machinery of an infected human cell and thus an antiviral drug must be remarkably selectively toxic if it is to inhibit the viral particle without adversely affecting the human cell.
- Comparison with antibacterial agents, very few inhibitors can be considered as being safe antiviral drugs, although the situation is improving. Possible sites of attack by antiviral agents include prevention of adsorption of a viral particle to the host cell, prevention of the intracellular penetration of the adsorbed virus, and inhibition of protein or nucleic synthesis. Genetic information for viral reproduction resides in its nucleic acid (DNA or RNA). The viral particle (virion) does not possess enzymes necessary for its own replication; after entry into the host cell, the virus uses the enzymes already present or induces the formation of new ones. Viruses replicate by synthesis of their separate components followed by assembly.
- A prophylactic is a medication or a treatment designed and used to prevent a disease from occurring.
- Vaccinia virus (VACV or VV) is a large, complex, linear dsDNA, enveloped virus belonging to the poxvirus family. Vaccinia virus is the active constituent of the vaccine that eradicated smallpox, making it the first human disease to be eradicated. Vaccinia virus is closely related to the virus that causes cowpox antiviral drug that works by inhibiting mRNA and protein synthesis, especially in pox viruses.
- Interferon is produced by the host cell in response to the virus particle, the viral nucleic and non-viral agents, including synthetic polynucleides such as polyinosinic acid: polycytidylic acid (poly I: C).
- Leucocytes- WBCs Fibroblast- a cell in connective tissue which produces collagen and other fibres. Fibrocytes are cells that circulate in the peripheral blood and produce connective tissue proteins such as vimentin and collagens I and III. Fibrocytes are associated with skin lesions, pulmonary fibrosis, and tumors and they contribute to the remodeling response by secreting matrix metalloproteinases.
- Acid-labile- decompose, or break down in some way in presence of an acid A T cell or T lymphocyte is a type of lymphocyte (a subtype of white blood cell) that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes, such as B cells and natural killer cells, by the presence of a T-cell receptor on the cell surface. They are called T cells because they mature in the thymus from thymocytes