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					                                       Antiviral Drugs


                    Organization of Class

                1) Vaccination is used to try to prevent and control the spread of the
                   disease.

                2) Chemotherapy: is used to treat the symptoms of viral illness and try to
                   eliminate the virus from the body.

                3) Stimulation of the hosts natural resistance mechanisms is used to
                   shorten the duration of illness.

                    Life cycle of the viruses:

                1)   Attachment and penetration of the viral to the host
                2)   Uncoating of he viral genome within the host cell.
                3)   Synthesis of viral components within the host cell.
                4)   Assembly of viral particles.
                5)   Release of the virus to spread and invade other cells.

                Most of the drugs that are currently available block specific proteins
       that are involved in synthesis of viral components within the host cell.

                 Drugs used in Influenza

                * the mainstay of protection against influenza has always been
vaccination.

                * New drugs are now becoming available that effectively treat infuenza

               * The protype drug is Amantadine thet is used in treatment and
prevention of influenza type A infections.

             * if begun within 48 hrs of the onset of illness , Amantadine shortens the
       symptoms by about half.

                * but its use is limited due to resistance and side effects.

                * Other group called: Neuraminidase inhibitors
                       - Ex: zanamivir
                       - M.O.A: block the release of influenza virus from the infected
       cells.
                        - Use: in influenza type A, B



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                       - can shorten the duration of illness if they are used within 30 hrs
       of the onset of symptoms.


                       Note: Neuraminidase is an enzyme located on the surface of the
       virus that plays an important role in the release of the virus from the surface of the
       infected cell.

                           Anti –HIV Drugs

       * Human immunodeficiency virus (HIV) is the virus that causes AIDS

        * HIV virus is a retrovirus, which means that it has specific enzyme called reverse
transcriptase that able to synthesize RNA from DNA.

        * Nucleoside drugs: Ex: zidovudine
         and non-nucleoside : Ex: delavirdine
these drugs are reverse transcriptase inhibitors ( i.e inhibit the formation of viral DNA
from RNA).

       * Protease inhibitors: Ex: ritonavir
       Interfere with processing of the viral protein, thus preventing the formation of
new viral particles.

        * Triple therapy: 2 reverse transcriptase inhibitors + 1 Protease inhibitor is
currently the most effective treatment for HIV.

        The 2 reverse transcriptase inhibitors are used due to the rapid emergence of
resistant virus.


                           Other Antivirals

        * Acyclovir: is used to treat patients with herpes infections, to be effective it must
be activated by triple phosphorylation.

                          - Used orally, topically, and IV for the treatment of herpes
infections.
                          - It inhibits the virus DNA polymerase.

        * Ribavirin: is the drug of choice in the treatment of respiratory virus infection in
infants and young children.

        * Interferon alfa: endogenous protein with multiple of actions,
used in hepatitis C, leukemia, myeloma, genital warts and multiple sclerosis.




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                         Anti-mycobacterium (Anti-TB)
        The chemotherapy of infections caused by Mycobacterium tuberculosis is
complicated by numerous factors, including
(1) Limited information about the mechanisms of antimycobacterial drug actions
(2) The development of resistance
(3) The intracellular location of mycobacteria
(4) The chronic nature of mycobacterial disease, which requires protracted drug treatment
and is associated with drug toxicities.

        Chemotherapy of mycobacterial infections almost always involves the use of drug
combinations to delay the emergence of resistance and to enhance antimycobacterial
efficacy.

      The major drugs used in tuberculosis are isoniazid (INH), rifampin,
ethambutol, pyrazinamide, and streptomycin.

      Actions of these agents on M tuberculosis are bactericidal or bacteriostatic
depending on drug concentration and strain susceptibility.

        Suppression of the mycobacterium in the immunocompromised patient also
requires multidrug treatment.




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                                  Antifungal Agents
A number of different antifungal agents are available. The available agents can be
classified as follows:

      Polyne macrolids antibiotics:

               Bind to sterol (ergosterol) in cell membrane forming cytotoxic pores.

               Ex: Amphotericin: used in fungal meningitis.
                  Nystatin: used in mucocutanous candidal infection.

      Penicillin derivative

               Inhibits fungal cell mitosis.
               Ex: Griseofulvin: Systemic fungal infection.

      Imidazoles

               Inhibit synthesis of ergosterol in cell wall.

               Ex: Ketoconazole: mucocutanous candidal infection
                                 Seborrheic dermatitis


                    Miconazole: Vulvovaginal candidiasis.

                    Clotrimazole: Oro-pharyngeal thrush
                                  Vulvovaginal candidiasis


      Triazole:

               Fluconazole: Mucocutanous candidiasis.

               Itraconazole:




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                                     Anti-Amebiasis




       Diloxanide Furoate:

        Diloxanide furoate is converted in the gut to the diloxanide freebase form, which
is the active amebicide. Toxic effects are mild and are usually restricted to
gastrointestinal symptoms.

       Metronidazole:

       Causes oxidative damage to DNA of trophozoite.

       Side effects: metallic taste, GI distress.




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                              Antihelminthic agents

* Mebendazole: inhibit microtubule synthesis and inhibit glucose uptake in nematodes.

              Used in: Pinworm infection
                       Whipworm infection.

* Pyrantel pamoate: causes paralysis of nematodes muscles.

              Use in: Hookworm infection.
                      Pinworm infection
                      Roundworm infection




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                                Anticancer Drugs
            General Principles

   Anticancer therapy is aimed at killing dividing cells. There are normal host cells
    that are also dividing. Effects on these cells cause side effects.

   It is difficult not to kill normal host cells because the cancer cells are also host
    cells that lose their control of cell division.

   Cancer cells can mutate in a way that makes them resistant to anticancer drugs.

   Combination of drugs are frequently used to treat cancer, this reduces the
    incidence of drug resistance.

   Log kill: the anticancer drugs kill a constant fraction of cells instead of an
    absolute number.

            Drug Classification

   Alkylating agents :
       - Nitrogen Mustards ex: cyclophosphamide,
               Mechlorethamine
       - Nitosoureas

   Antimetabolites
       - Folate antagonist . ex: methotrexate
       - Purine analogues: ex: mercaptopurine
       - Pyramidine analogues

   Antibiotics: ex: Daunorubicin, vincristine.

   Hormonal agents: ex: tamoxifen


            Adverse effects

 Because anticancer aimed to kill dividing cells, so the highly dividing normal
  cells in the body may be killed.
                  Ex: GI tract epithelium , hair follicle, bone marrow.

 Bone marrow destruction is caused by destruction of stem cells, this lead to
  decrease blood elements including white cells and platelets.

 GI toxicity: Nausea and vomiting due to central effects and damaging of GI
  mucosa.


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 Destruction of hair follicle produces hair loss.

 Methotrexate: Renal tubular damage as side effect.

 Doxorubicin: Cardiotoxicity as side effect.

 Vincristine: nervous system toxicity.


           Alkylating agents:

   The most widely used antitumor agents.

   Add alkyl group to DNA

   Mechlorethamine: used in lymphoma
    Nitosourea: brain tumor


           Antimetabolites

   Compete for binding sites on enzymes or can be incorporated into DNA or RNA.

   Methotrexate inhibits dihydrofolate reductase.

   Methotrexate is used in psoriasis and severe rheumatoid arthritis..

   Mercaptopurine: is used in leukemia and lymphoma

           Antibiotics

   They disrupt DNA function.

   Daunorubicin: is used in acute leukemia.


           Hormonal agents

   They are used to treat hormonally sensitive tumors, such as tumors of breast,
    prostate and uterus.

   Tamoxifen: is estrogen antagonist, used in the treatment of breast cancer.

   Flutamide: testosterone antagonist used in treatment of prostate cancer.




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posted:11/17/2011
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