Page 183 - MNU-PM502- Pharmaeutical Microbiology Theoritical Book

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

In case of antagonism: 1 < FIC index

Isobologram bend to the outside.

2- Time-kill test

The results are expressed as the early bactericidal rate or as the smallest
concentration of drug capable of killing number of bacteria in a certain time.

Kinetic killing curves have advantages over checkerboard titrations because they
provide a dynamic assessment of bactericidal activity.

This method uses the log survivors-time curve as measures of single and combined

drug action.

1- Synergism: the drugs in combination produce a greater value in the bactericidal
rate than that produce by twice the concentration of either drug alone

synergy is defined as a > 100-fold increase in killing at 24 hours as compared with
the most active single agent.

2- Addition: the bactericidal rate of the drugs in combination is approximately
equal that expected from simple algebraic summation of single drug effect

3- Antagonism: the bactericidal rate of the drug combination is below that of one
or both of its component and at least a 100-fold decrease in killing as compared
with the most active single agent.

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