C1. General considerations of antimicrobial therapy. Disinfectants and antiseptics Flashcards
What are the different indications for Antibiotics?**
- Prophylactic - surgery, etc. to prevent future infection
- Empirical - based on past evidence of which bacteria are common in certain types of infection, showing certain symptoms etc. → treat without definite culture / diagnostic positivity. Most common; sometimes not effective. If more severe (endocarditis, meningitis, pyelonephritis, etc.) take sample, culture and sensitivity test (antibiogram).
What are disinfectants?
Disinfectants are chemical liquids that destroy bacteria.
What is Antiseptic?
Antiseptic means preventing the growth of disease-causing microorganisms.
What is the efficacy of a antibiotic?
Efficacy depends on sensitivity of microbe + reaching therapeutic conc. at site of infection.
What is the difference between Narrow and Broad-Spectrum?
- Narrow spectrum is active against 1-2 groups bacteria.
- ex: vancomycin against gram-pos. anaerobe / aerobes.
- usually in specific treatment when microbe is identified + antibiogram’d.
- Broad spectrum is against more than 2 groups.
- ex: carbapenams against gram-pos/neg aerobe/anaerobes (but not IC!).
- usually for empiric treatment
What is the Post-Antibiotic Effect (PAE)?
- It is a period of time necessary until abx concentration decreases and bacteria returns to logarithmic growth
- graph: looks like slopey drop of [abx] until below therapeutic conc. (dotted horizontal line) → bacterial growth returns (different line slopes up)
- due to slow recovery after non-lethal damage to some of the pathogenic microbe OR persistence of drug in periplasmic space OR period of new enzyme synth by remaining bacteria to continue growth
- in gram-positive, PAE is common; in gram-negative is uncommon. aminoglycosides + fluoroquinolones also have PAE with gram negs!
How is the dosing done for antibiotics?
- newborns have higher extracellular space
- elderly have slower metabolism
- ex: aminoglycosides - hydrophilic and don’t enter fat → lower dose for obesity, higher for newborns (due to ↑ IC space)
What are the common side effects of antibiotics?
- CNS - epileptic seizures (beta-lactams at high serum levels)
- Nephro- / Ototoxicity - aminoglycosides
- Hepatotoxic - most 1st line anti-TBCs
- Safe in pregnancy - beta-lactams and macrolides
Why do we combine antibiotics?
- Combining antibiotics was more done in the past to broaden the spectrum, however now we have broad-spectrum abx.
- We do still combine to further broaden the spectrum or for synergism.
- Examples: beta-lactam + aminoglycosides - b-lactam inhibits cell wall → AG can access intracellular space (severe staph → oxacillin + gentamicin; severe multi-resistant enterococci → ampicillin + gentamicin; resistant pseudomonas → piperacillin + gentamicin)
How long is the duration of action of antibiotics?
It depends on the cause: examples…
- 3-5 days in uncomplicated infection (UTI in women)
- 7-10 days if more severe (acute pneumonia)
- chronic condition / difficult to reach area - 3-6 weeks (chronic prostatitis)
- tuberculosis - 6 months+
- osteomyelitis - 4-6 months
What are concentration dependendent antibiotics?
- Their effects depends on how much time spent at conc. higher than MIC.
- Can obtain better effect with higher dose.
- Ex: aminoglycosides; usually 1x/day high dose
What are concentration and time dependent antiobiotics?
- They are basically conc. dependent but resistance is common
- To avoid formation of resistant mutants, give high conc. for long term
- Ex: fluoroquinolones
What are Time-Dependent Antiobiotics?
Time-Dependent - effect depends on how long conc. is higher than MIC (how is this diff?)
Ex: beta-lactams, usually given several times/day
How is the tissue penetration of antibiotics?
Some areas are not easily penetrable by abx.
- CNS - can inject intrathecally
- Ischemic areas
- Bone - fluoroquinolones penetrate bone
- Prostate - fluoroquinolones penetrate prostate
What are bactericidal antibiotics?
- Bactericidal antibiotics kill bacteria.
- Bactericidal antibiotics are used if patient has low immune function (neutropenic) or life threatening conditions (osteomyelitis, endocarditis, meningitis, etc.)
- ex: chloramphenicol, clindamycin, tetracyclines, macrolides (usually)
