1. Intro to Antibiotics
By: Alaina Darby

2. Outline Intro to Antimicrobials Overview Specific Things to Remember
Helpful Tips for the Test
Practice Questions

3. Intro to Antimicrobials Overview

4. Antibiotic vs Antimicrobial
Antibiotics
Produced by a microorganism
Most of the older antimicrobials can be classified as antibiotics and are, therefore, classified as antibiotics and antimicrobials
Example: penicillin
Antimicrobials
Antibiotics are a subset of antimicrobials
Antimicrobials inhibits growth or kills microorganisms
Many newer antimicrobials are not natural products, so they are antimicrobials but not antibiotics

5. Terms Gram stain Selective toxicity Post-antibiotic effect (PAE)
Bactericidal
Bacteriostatic
Spectrum
Biofilm
Synergy

6. Concentration vs Time-Dependent Killing
Concentration-dependent
Cmax/MIC
Cmax is the peak concentration
Kills at high concentration but doesn’t really matter as much how long they are at the high concentration
Can have longer dosing intervals
These have a long PAE
Example: aminoglycosides
Time-dependent
T>MIC
Has to be above the MIC for an extended period of time but really high concentrations don’t usually increase killing
Can give smaller doses more frequently
If you are giving the drug IV, then a continuous infusion is good
Has little to no PAE
Example: vancomycin

7. Choosing Antibiotics DIAGNOSIS!! Specificity/Spectrum
Bactericidal/Bacteriostatic
PAE
Site of infection
Other factors at the site of infection
Host factors

8. Site of action A (aminoglycosides) T (tetracyclines)
Helpful memory aid:
Think about the stock market. When you play the stock market, you want to buy low and sell high.
There are 2 subunits of the ribosome – 50S and 30S.
So… A smart person buys AT 30 and CELS for 50.
AT:
A (aminoglycosides)
T (tetracyclines)
CELS:
C (clindamycin/chloramphenicol)
E (erythromycin/other macrolides)
L (linezolid)
S (streptogramins)

9. Resistance Intrinsic vs Acquired Mechanisms Intrinsic: already present
Acquired: mutation or transmission of genes
Mechanisms
Receptor alteration
Decreased transport into microorganism
Increased export (e.g. tetracyclines)
Inactivation (e.g. beta-lactams, aminoglycosides)
Alternative metabolic pathways (e.g. TMP/SMX)
Defect in activation (e.g. metronidazole, 5-flucytosine)

10. Specific Things to Remember
Important points for certain bugs and drugs.
Specific Things to Remember

11. Metabolism/Excretion
Almost everything that works on the cell wall is renally excreted.
Almost everything that works anywhere else is metabolized.

12. Spectrum Gram negatives only Pseudomonas MRSA Anaerobes VRE
Aztreonam
Pseudomonas
Cefepime
Ceftazidime
Piperacillin/Tazobactam (Zosyn)
MRSA
Vancomycin
Ceftaroline
Linezolid
Streptogramins
Daptomycin
Anaerobes
Clindamycin
Metronidazole
VRE
Linezolid
Streptogramins (faecium only)
Daptomycin
Cephalosporines DO NOT treat enterococcus!

13. Adverse Effects Almost everything can cause GI disturbances
Aminoglycosides
Nephrotoxicity
Ototoxicity
Tetracyclines
Dental discoloration
Photosensitivity
Fluroquinolones
Tendon ruptures
Penicillins (and sometimes Cephalosporins)
Hypersensitivity
Clindamycin
C. difficile infection
Chloramphenicol
Gray baby syndrome
Telithromycin
QT prolongation
Sulfonamides
Hypersensitivity
Hematologic (G6PD deficiency)
Kidney stones
Metronidazole
Disulfram-like reaction
Isoniazid
Liver failure

14. Drug Interactions Tetracyclines Macrolides Rifampin Ca2+ chelation
Strong CYP inhibitors
Especially erythromycin
Exception: azithromycin
Rifampin
Induces everything

15. Helpful Tips for the Test
Some fun memory aids for you!

16. Clindamycin has good activity in the bone
Clindamycin has good activity in the bone. (That was a question my P1 year!)
Tigecycline is hepatically and renally excreted… Tigers poop and pee a lot. (I didn’t come up with that.)
TMP/SMX treats…
T: Tree (respiratory)
M: Mouth (GI tract)
P: Pee (genitourinary)
S: Syndromes (AIDS… like PCP)
CefTAZidime and cefEPIme are the only cephalosporins that are EPIc enough to TAZe Pseudomonas.
Quinolones are a “flock of sinners” (-floxacins) that gyrate (DNA gyrase) their hips at night (photosensitivity). They dance and party so much that their tendons rupture and they have heart problems (QT prolongation).