antibiotics Flashcards
There are 2 mechanisms of antibiotic action name and explain them and give examples of these drugs
- MOA1: Concentration depended killing
-example:Aminoglycosides and Quinolones
- This drugs their killing o the organism is depended on the concentration
- CURVE-> MIC ( minimum inhiitory concentration ->minumum concentration required to inhibit the groth of the organism ), therefore the area under the curve and the curve divided by the MIC correlates to the amount needed to eradicate the organism )
- The important thing about these drug is to not underdose (make sure the concentration is enought ) - MOA2: Time depedent killing
- examples: Beta lactams
- the concentration of these drugs need to be about MIC for a certain amount of time e.g in Meningitis -> must be above MIC 95-100% of the time
-Generally but be above MIC 40-60% of the time
- in this drugs increasing the concentration does do do must , what is important is the intervals that you gibe the medication .
Therefore it is important that you do not miss doses and make sure that the intervals that you give the drug are correct .
what is the MOA for beta lactams ?
- Act on the cell wall - inhibits formation of peptidoglycan cross-links ,hindering bacterial cell wall synthesis
- they have time dependent bactericidal action
- they have wide therapeutic indux ( they are CNS toxic at maximal doses )
- Most eliminated by renal tubular secretion
- main adverse effect is HYPERSENSITIVITY
what Commonest resistance mediated by β-lactamases?
- Commonest resistance is caused by beta lactamases :
- this one cannot be overcome by using higher doses
- In community most aerobic Gram negatives, anaerobes & staphylococci
produce β-lactamase( enzyme produced by the bacteria against beta lactams/)
- Extended spectrum β-lactamases in aerobic Gram negatives in hospitals,
which results in high level resistance to all penicillins & cephalosporins
2 .Second resistance mechanism is mutations in penicillin binding proteins
(e.g. S. pneumoniae) – usually low level resistance, which can be
overcome by using higher doses
list drugs that fall under beta lactams
- Penicellins =4
-Penicilllin
- Aminopenicillin -> ampicilin and amoxicillin
- Cloxacillin
- Flucloxacillin - Cephalosporins =
- first gene->Cefazolin and Cephalexin
-2nd gene -> Cefuroxime
-3rd gene ->Cefotaxime/ceftriaxone and Ceftazidime
-4th gene->Cefepime - Carbapenems
Which group of organisms is Penicillin active against and the conditions in which it is used as drug of choice ?
- Penicillin is active against Gram positives, & spirochaetes
- Drug of choice for
– Streptococci (few S. pneumoniae highly resistant)
– Syphilis & other spirochaetes
– Enterococci
– Listeria
– Actinomyces
(however it is susceptible to beta -lactamase-> resistance )
in what route is penicilin given in ?
Penicillin G IVI, pen V oral (poorly absorbed –
concentrations inadequate for S. pneumoniae)
- Long-acting injectable benzathine penicillin (IMI) lasts for
21 days.
Give 2 example of Aminocillins and their route of administration
- Ampicillin (only useful IV)
- Amoxicillin (oral – well absorbed)
Which group of organisms is Aminopenicillins active against and the conditions in which it is used as drug of choice ?
- Initially were broad spectrum agents, but
resistance has become widespread - they cover :
1. Gram positives, & spirochaetes
2. Drug of choice for
– Streptococci (Excellent activity against S. pneumoniae, therefore
recommended for respiratory infections)
– Syphilis & other spirochaetes
– Enterococci
– Listeria
– Actinomyces
-Haemophilus
(except
those +15% that have β-lactamase)
what are Cloxacillin and Flucloxacillin used for ?
-Both only for Gram positive bacteria
-Widely used for skin and soft tissue infections
name one advantage of Cloxacillin and one for Flucloxacillin
Cloxacillin resists β-lactamase from Staphylococci
Flucloxacillin better absorbed orally
Name 2 irrevesible inhibitors of beta-lactamases and how are they used
-Clavulanate
– Tazobactam
use :
- they are comined with beta-lactams -> Combined with β-lactams can reverse resistance
– Amoxicillin-clavulanate – broad spectrum
community-acquired Gram positive, Gram negative &
anaerobe infections
– Piperacillin-tazobactam- hospital
what are the 1st gene cephalosporins and which spectrum of organisms do they cover ?
1st generation (spectrum largely limited to Streptococci &
Staphylococci)
– Cefazolin IV
– Cephalexin PO
what are the 2nd gene cephalosporins and which spectrum of organisms do they cover ?
2nd generation (spectrum as for 1st generation PLUS
Haemophilus, community-acquired Gram negatives)
– Cefuroxime PO & IVI
what are the 3rd gene cephalosporins and which spectrum of organisms do they cover ?
3rd generation (2nd PLUS typhoid, spirochetes, good CSF
penetration)
– Cefotaxime/ceftriaxone
– Ceftazidime (Pseudomonas – poor for Streptococci)
