Page 178 - MNU-PM502- Pharmaeutical Microbiology Theoritical Book

Pharm D- Clinical Pharmacy Program Third Level Pharmaceutical Microbiology& Antimicrobials (PM 502)

Antimicrobial Combinations

Indications for combination antimicrobial therapy:

A. Empirical treatment of life-threatening infections
• To achieve adequate cover of the range of possible pathogens before full
diagnosis is reached (empirical therapy)

• It will often include an agent broadly active against Gram-positive and Gram-
negative bacteria
B. Treatment of polymicrobial infections.

• When not all organisms are susceptible to the same antibiotic e.g. peritonitis,
leg ulcers in diabetic patients (mixture of aerobes, anaerobes, G+ve and G-ve
organisms)

C. Prevention of the emergence of bacterial resistance.
D. Decrease toxicity

Ability to use non-toxic amounts of two antibiotics when toxic doses of a single
antibiotic would be required

e.g. use of triple-sulfonamide combinations to avoid the crystalluria observed
when relatively insoluble sulfonamides were used in full doses.

E. Synergism

When a combination therapy may be more effective on a single organism than the
use of one antimicrobial agent alone

Types of interactions

Antagonism

• A negative interaction between two drugs

• less antimicrobial activity with a combination of drugs than with the use of
either agent alone (1+1<1).

e.g. inducers of  -lactamase (Cefoxitin and imipenem) + other  -lactam

antibiotics

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