Drugs for Fungal, Viral, and Parasitic Diseases

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Drugs for Fungal, Viral, and Parasitic Diseases

• Chapter 23

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Fungi

• Many normally exist on human skin and mucus
  membranes
• These are held in check by other
  naturally-occurring microbes
• Systemic infections commonly occur in those with
  suppressed immune systems (patients with AIDS, on
  chemo, organ transplants, or long term steroid
  therapy)
• Mycoses- Fungal infection
• Superficial/dermatophytic affect scalp, skin,
  hair, nails and MM (oral cavity and vagina)
  usually mild and may be treated topically
• Systemic- affect internal organs (lung, brain,
  etc) quite serious and usually require
  aggressive oral or parenteral therapy

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Systemic Antifungals (amphotericin B)

• Broad spectrum used for severe infections IV
  use only
• Binds to fungal membranes to allow leakiness
• SE fever, chills, phlebitis, nephrotoxicity
• Newer azoles (ketoconazole, fluconazole) are less
  toxic and may be given orally

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Superficial antifungals (nystatin)

• Affect cell wall to cause leakiness
• Usually administered topically
• Few SE

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Viruses

• Non-living particles consisting of only a few
  dozen genes
• Use machinery of hosts cell to replicate
• Most are self-limiting
• Rapid mutation and development of resistance
  makes antiviral therapy difficult
• Antivirals are often toxic because they must also
  attack the host cell

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Human Immunodeficiency Virus

• Retrovirus- has RNA instead of DNA as its genetic
  material. Uses enzyme called reverse
  transcriptase to become part of the host cells'
  DNA. This allows many copies of the virus to be
  made in the host cells.
• Mutation with resistance occurs quickly, so new
  drugs are constantly needed and 3-4 drugs are
  used concomitantly
• Recently, US HIV death rate has significantly
  declined (for the following reasons)
• Therapy allows clients to remain symptom-free for
  a longer time
• Transmission from HIV mother to newborn has
  dropped dramatically due to antiretrovirals

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Antiretrovirals (zidovudine or AZT)

• Inhibits the viral enzyme reverse transcriptase,
  which is necessary for replication
• SE anemia, anorexia, n/v, weight loss

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Antiherpes drugs (acyclovir)

• Herpes Simplex Virus (HSV) causes recurrent
  episodes of blisters that rupture
• Acyclovir interferes with DNA synthesis
• May be given episodically or continuously

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Antiinfluenza drugs

• Flu symptoms fever, sore throat, coughing may
  be fatal
• Amantadine, rimantadine, osteltamivir, and
  zanamivir are available and have been used for
  treatment (shortening course from 7 to 5 days)
  and prophylaxis
• Most current influenza cases are resistant to
  amantadine and rimantadine

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Avian Influenza

• Caused by influenza viruses that occur naturally
  in wild birds (these birds are typically
  unaffected)
• Easily transmitted to domesticated birds, with
  high fatality rate
• Several subtypes have infected humans (140 cases
  since 1/2004), usually these are cases of people
  who had contact with infected birds
• Half of those infected have died
• Human-to-human spread is rare and has so far not
  continued beyond 1 person. Increased human
  transmissibility could lead to pandemic
• Amantadine and rimantadine not effective.
  Oseltamivir and zanamavir may be useful.

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Antiparasitic agents (metronidazole)

• Parasites may be protozoa, worms, or ticks
• Uses amebiasis (infection of amebas in intestine
  and liver), trichomonas, bacterial vaginosis
• SE GI upset, metallic taste in mouth,
  disulfiram-type reaction with alcohol

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