Antibiotic combinations

Question 1

What are the general principles of antimicrobial selection

Answer 1

Apply principles of good stewardship

Use planned antimicrobial treatments when possible.

Perform culture and sensitivity testing (C&ST) to guide antibiotic choice.

For empirical treatment, select antibiotics based on likely pathogens.

Question 2

Why are antibiotic combinations used in practice?

Answer 2

To treat mixed infections with pathogens resistant to single agent

To achieve synergistic effects against resistant strains (e.g., Pseudomonas aeruginosa).

To reduce or overcome bacterial resistance.

Question 3

What considerations should be made when choosing antibiotic combination therapy?

Answer 3

Combinations need to be different targets or process

OR

Need to be different points on the same process.

Question 4

What is synergy in antibiotic combinations

Answer 4

Synergy: combined effect is greater than sum of individual effects

Example: Clavulanic acid with amoxicillin.

Question 5

What is additive effect of antibiotic combinations

Answer 5

where there is a benefit for treatment but does not increase individual activity

e.g. Combining antibiotic for anaerobes with one for aerobes broadens spectrum without enhancing each other’s activity

Question 6

What are examples of synergistic combinations

Answer 6

Clavulanic acid + amoxicillin: Clavulanic acid inhibits beta-lactamase, protecting amoxicillin

Penicillins + aminoglycosides: Penicillins disrupt cell wall, enhancing aminoglycoside uptake

Question 7

What are examples of incompatible antibiotic combinations?

Answer 7

Beta-lactams with bacteriostatic antibiotics: Bacteria stop growing, reducing beta-lactam efficacy.

Procaine penicillin-G with sulphonamides: Procaine metabolizes into PABA, which reduces sulphonamide efficacy.

Question 8

What should you avoid when using antibiotic combinations

Answer 8

Avoiding drugs that contain products that inactivate or interfere with other antibiotics

Avoiding drugs with same target/activity (will not add benefit)

Drugs where they may interact and affect their function.

Question 9

Give examples of bacteriocidal antibiotics

Answer 9

penicillins,
cephalosporins,
aminoglycosides,
trimethoprim/sulfonamides (“potentiated”),
metronidazole,
quinolones,
rifampin,
glycopeptides

Question 10

Give examples of bacteriostatic antibiotics

Answer 10

tetracyclines,
phenicols (eg, chloramphenicol, florfenicol),
macrolides,
lincosamides,
spectinomycin,
sulfonamides (non-potentiated)