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Infectious Diseases

Infectious Disease information and resources for the MSK community, including clinicians, patients, and the general public.

Types of Antimicrobials

Antimicrobials are substances that kills microorganisms or stop them from growing and causing disease. Antimicrobials are grouped according to the type of organism it acts against; antibacterials against bacteria, antivirals against viruses, antifungals and antiparasitics against fungi and parasites.

Antibacterial Drugs

Antibacterial drugs are derived from bacteria or molds or are synthesized from scratch in a lab. Technically, “antibiotic” refers only to antimicrobials derived from bacteria or molds but is often used synonymously with “antibacterial drug.”

Antibiotics have many mechanisms of action, including the following:

  •  Inhibiting cell wall synthesis 
  • Increasing cell membrane permeability 
  • Interfering with protein synthesis, nucleic acid metabolism, and other metabolic processes (eg, folic acidsynthesis)       

Antibiotics sometimes interact with other drugs, raising or lowering serum levels of other drugs by increasing or decreasing their metabolism or by various other mechanisms. The most clinically important interactions involve drugs with a low therapeutic ratio (ie, toxic levels are close to therapeutic levels). Also, other drugs can increase or decrease levels of antibiotics.

Many antibiotics are chemically related and are thus grouped into classes. Although drugs within each class share structural and functional similarities, they often have different pharmacology and spectra of activity. 

Antiviral Drugs

Antiviral drugs are used to treat viral infections. Most antivirals target a specific virus (e.g. Tamiflu targets the Influenza virus), though there are some broad-spectrum antivirals on the market.  Most antiviral agents are only effective while the virus is replicating. There are also preventative antiviral drugs that  protect you from getting and/or spreading a virus; the most common of which are vaccines.

Antivirals can work in any of three ways:

  • Targeting and blocking the virus's receptors so it cannot attach to and enter healthy cells
  • Lowering the amount of active virus (viral load) in the body by deactivating the virus's replication process
  • Boosting the immune system by teaching it to identify a virus and destroy it

Antifungal Drugs

Antifungal (antimycotic) drugs treat fungal infections by either killing the fungus or stopping its growth. Many antifungal treatments for common fungal infections (eg. Athlete's Foot), are available over-the-counter. However, for more complex fungal infections a prescription antifungal is necessary. Antifungals can be administered topically (creams or ointments that go directly on the skin infection), orally, or intravenously.

There are three classes of antifungal treatments:

  • Azoles stop the fungus from growing
  • Echinocandins attack and damage the fungus cell wall
  • Polyenes destroy the fungus cell

Antiparasitic Drugs

Antiparasitic drugs are a group of medications used in the management and treatment of infections by parasites. Antiparasitic drugs are classed by the type of organism they act against.

  • Antiprotozoals treat protozoan infections through a variety of mechanisms by inhibiting key parasitic processes
  • Antihelminthics expel helminths (parasitic worms) from the body by either stunning or killing them without causing damage to the host
  • Antiamoebics treat Amebiasis, a bowel infection caused by the parasite Entamoeba histolytica
  • Nitazoxanide is a broad-spectrum antiparasitic and antiviral drug used to treat various helminthic, protozoal, and viral infections