Medical Pharmacology Chapter 35  Antibacterial Drugs

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Anthrax

  • Anthrax is a bacterial infection caused by Bacillus anthracis.

  • Spores of Bacillus anthracis may be introduced by:

    • Animal contact

    • Contact with infected animal products

    • Inhalation

    • Ingestion

    • Insect bites.

  •  B. anthracis is a chain-forming, aerobic gram-positive rod which can form oval spores.

  •  B. anthracis is an extracellular organism that:

    •  Multiply rapidly

    •  Release anthrax toxins and capsular polypeptides release

    •  Prevent host phagocytosis.

  • Anthrax toxin consists of three proteins:

    • Protective antigen (PA)

    • Edema factor (EF)

    • Lethal factor (LF).

      • Entry of LF results in cell death by a yet to be elucidated mechanism.

    Main clinical manifestations:

    • Cutaneous anthrax- 95% of anthrax is cutaneous.

    • Most untreated cases resolve (80%-90%)

    • In 10%-20% a progressive infection leads to bacteremia and death.

  •  Inhalation anthrax:

    1. Cases present with symptoms similar to severe respiratory viral infection.

    2. With three days, the disease progresses with increasing fever, dyspnea, hypoxia, and hypotension and usually leads to death.

  • Parentral penicillin G is highly effective in treating cutaneous anthrax.

    • With penicillin sensitivity, ciprofloxacin, erythromycin, tetracycline, or chloramphenicol may be used instead.

  • For inhalation or gastrointestinal anthrax, high-dose penicillin treatment is recommended.

    • With appropriate treatment the mortality rate for cutaneous anthrax is very low.

    • The mortality rate for gastrointestinal anthrax is about 50%, if treated.

    • The mortality rate for inhalation anthrax may approach 100% if symptoms are not promptly recognized and treated.

    • The likelihood of an adverse outcome is also probably dependent on the number of spores inhaled.

      • There are (2001) examples of individuals who recover from inhalation anthrax.

Holmes, R.K., Diphtheria, Other Corynebacterial Infections and Anthrax, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, p. 897-899.

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