Anti viral Medicines Information

 

The viruses require active participation of the metabolic processes of the invaded host cells. In turn, the agents that may inhibit or kill the viruses are also very likely to injure the host cells. This intimate relationship between the virus and the host cell makes the possibility of selective antiviral action difficult to achieve. Many effective antiviral agents cannot be used in clinical practice because of their extreme toxicity towards host cells. The development of useful antiviral drugs has lagged far behind that of antibacterial agents.

Types of Viruses

Viruses can be divided into: (i) the large viruses (Chlamydia) responsible for molluscum contagiosa, trachoma, inclusion conjunctivitis, lymphogranuloma venereum and the rickettsial infections; and (ii) the true (small) viruses including the pox viruses, herpes viruses and adenoviruses viruses. The large viruses possess both DNA and RNA, and differ from true viruses both in morphology and in their mode of multiplication. They show varying susceptibility to the penicillin, tetracycline, chloramphenicol and the sulphonamides.
The true viruses contain a core of either DNA (smallpox, chickenpox, herpes simplex, herpes zoster), or RNA (poliomyelitis, mumps, measles, rabies), but never both.

Antiviral Drugs

The antiviral drugs described below are used in U treatment of a number of viral infections, or provide protection for a brief period of time. Treatment must be started early to be effective by inhibiting the replicating virus.

Antiviral Drugs Types

According to their mode of action the antiviral drugs can be classified as under:
1. Inhibitors of adsorption and penetration

Gamma Globulin 
Gamma globulin (IgG) is a fraction obtained from the plasma of normal individuals, and is rich in most of the antibodies found in whole blood. It contains a variety of antibodies against specific viral antigens.

Ribavirin 
Ribavirin is a synthetic nucleoside analogue similar to guanine. It is used in the treatment of respiratory syncytial viral infections in infants and children, generally administered by inhalation through a small-particle aerosol generator.

Idoxuridine 
Idoxuridine is a structural analogue of thymidine, an essential intermediate in DNA synthesis.

Foscarnet 
Foscarnet sodium is a simple inorganic phosphonate analogue, which inhibits viral DNA polymerase and reverse transcriptase by interacting with the pyrophosphate binding sites on these enzymes.

Vidarabine
Vidarabine is an analogue of adenosine. It is least toxic and most effective of the purine analogues.

Acyclovir 
It is relatively more effective against human CMV infection. It is more than 100 times more active than Vidarabine, and 10 times more active than Idoxuridine against herpes simplex type-1 virus.

Desciclovir 
Desciclovir is an acyclovir prodrug, and provides higher plasma acyclovir concentrations than acyclovir on oral administration.

Trifluridine 
Trifluridine is a fluorinated pyrimidine deoxynucleoside which inhibits viral DNA synthesis.

Zidovudine 
The efficacy of zidovudine in patients with AIDS (who usually also have Pneumocystis pneumonia), and in symptomatic patients with AIDS-related complex (ARC) is well established.

Interferon 
The enhanced production of the antiviral protein called interferon is one of the body\'s earliest responses to a viral infection.
Interferon alpha is currently used for leukemia, AIDS-related Kaposi’s sarcoma candyloma (genital warts), and chronic hepatitis.

Amantadine is used for the prophylaxis and treatment of infection with influenza A virus. Influenza virus vaccine is the preferred method of prophylaxis. It is also useful in the treatment of parkinsonism.

Rimantadine 
Rimantadine is as effective as Amantadine in the prophylaxis and treatment of influenza A virus infection. It is claimed that the frequency of CNS side effects is lower compared to Amantadine.

Rifampicin 
Rifampicin prevents the assembly of enveloped mature viral particles. It is not useful in the treatment of human poxvirus infections, but topical application can inhibit human vaccine lesions. It is a primary drug used for the treatment of tuberculosis.


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