Introduction to Antimicrobials and Drug Susceptibility

Vocabulary flashcards covering types of antimicrobials, the Kirby Bauer susceptibility test, and the calculation of the therapeutic index.

Antimicrobials

Agents used to prevent and treat infections caused by microorganisms by acting against them.

Antiviral

Medications used against viruses, often ending in the suffix ‘vir,’ such as Acyclovir.

Antibiotic

Medications that act against bacteria, such as Amoxicillin or Penicillin.

Antiparasitic

Drugs used to treat infections caused by parasites, such as roundworms.

Antifungal

Medications used to treat fungal infections like athlete’s foot; examples include Lotrimin and Tenactin.

Microbicidal

A characteristic of a drug that means it kills the microbes rather than just inhibiting their growth.

Microstatic (Bacteriostatic)

A characteristic of an agent or method that stops or slows microbial growth but does not kill the bacteria.

Soluble

The ability of a drug to be dissolved in water easily for administration or absorption.

Susceptibility

The determination of whether a particular antimicrobial drug is effective at working against a specific microorganism.

Agar

A gelatin-like substance derived from algae used to create plates for growing bacteria in a laboratory.

Kirby Bauer disc diffusion method

A test for drug susceptibility where paper discs soaked in antimicrobials are placed on an agar plate containing bacteria.

Diffusion

The process by which particles move from an area of high concentration to an area of low concentration.

Zone of inhibition

A clear ring where no bacterial growth occurs around an antimicrobial disc; a larger zone indicates a more effective drug.

Resistant ($R$)

A classification indicating that a drug does not work well against a particular strain of bacterium.

Susceptible ($S$) or Sensitive

A classification indicating that a drug is effective against a particular strain of bacterium.

Intermediate ($I$)

A classification indicating that a drug's effectiveness against a bacterium falls somewhere in the middle between sensitive and resistant.

Therapeutic Index ($TI$)

A ratio comparing the toxic dose ($TD_{50}$) of a drug to its therapeutic or effective dose ($ED_{50}$), serving as a measure of safety.

Effective Dose ($ED_{50}$)

The concentration or dose of a drug that produces a therapeutic effect in $50\%$ of the population.

Toxic Dose ($TD_{50}$)

The concentration or dose of a drug that is toxic to $50\%$ of the population.

High Therapeutic Index

A value greater than $10$ indicating a safer drug with a larger ‘buffer’ or room for error, such as Tylenol ($TI=40$).

Low Therapeutic Index

A value less than $10$ indicating a less safe drug with a small room for error, such as Warfarin, Lithium, or Digoxin.

Warfarin

A medication with a very low therapeutic index (approximately $1$ or $2$) where there is virtually no room for error in dosing.

Digoxin (Digitalis)

A heart medication derived from the foxglove plant that is lethal in high doses but effective when synthesized and given in exact amounts.