Antibacterial agents Flashcards
definition of antibiotics
chemical product of microbes that inhibits or kills another organism.
OR
Natural substance produced by micro-organisms to kill each other.
Define antimicrobial agents
drugs used to kill organism.
synthetic- similar effect to antibiotics
semi synthehtic- modified from antibiotics.
2 types of bacterial killing
Bacteristatic- inhibit bacterial growth
Bactericidal- kills bacteria.
Define MIC
Minimal inhibitory concentration
concentration of antibiotic at which visible growth is inhibited.
Synergism
activity of 2 antimicrobials together is greeter than the sum of their activity separately.
Antagonism
one agent dimities the effect of another.
Indifference
activity unaffected by that of another.
Antibiotic targets include:
cell wall protein synthesis DNA synthesis RNA synthesis Plasma membrane
Main component of bacterial cell wall
Peptidoglycan
found in gram +ve and -ve.
2 cell wall synthesis inhibitors
B lactam- affect peptidocylcan cross linking
Glycopeptides.- affect peptidoglycan cross linking.
B lactams include:
penicillins- amoxicillin
Cephalosporins- cefuroxime
Carbapenems- meropenem, imipenem
Monobactams- aztreonam
Glycopeptide only work on what type of bacteria.
gram +ve bacteria.
cannot penetrate gram -ve outer membrane.
Most common example of a glycopeptide
vancomycin
Types of protein synthesis inhibitors.
Aminoglycoside
Macrolides Lincosamides Steptogramins (MLS)
Tetracyclines
Oxadolidilones
Most common amincoglyoside and mechanism of action
Gentamicin
bind to 30s subunit
Most common MLS and mechanism of action.
Erthromycin
Cindamycin
Bind to 50 s subunit
Most common Tetracylcines and mechanism of action
Doxytetracycline
bind to 30s subunit
Most common Oxazolidinones and mechanism of action
Linezolid
Bind to 50s or 70s subunit.
Types of DNA synthesis inhibitors.
Trimethoprim +sulphonamide= Co-trimoxazole.
Quinolones and fluoroquinolones
Co-trimooxazole mechanism of action
inhibit folate synthesis by inhibiting- dihydropteroate synthetase.
Most common Quinolones and fluoroquinolones and mechanism of action
Ciprofloxacin
Inhibit 1 or both DNA gyrase and topoisomerase.
RNA synthesis inhibtior
Rifampicin.
Rifamcin mechanism of action
prevents the synthesis of mRNA
Uses of colistin
last line drug when resistance to everything has been proved.
What type of bacteria is daptomycin used to treat.
Gram +ve
inserts lipophilic tail into cell membrane result in depolarisation
General side effects
Nausea, vommiting, headahce and skin rashes.
Side effects of aminoglycoslides
Reversible renal impairment on accumulation
Irreversible ototoxicity.- ear.
Side effects of B lactams
allergic reactions
side effect of linezolid
bone marrow depression
What causes c.difficile
to over use of antibiotics.
Strategy of antibiotic use
1- Empiric therpay- best guess therapy
2-targeted therapy- predict susceptibility and infecting organism
3-susecptibilty guided treatment- based on cultures.
How do you treat bacterial infections
Initially broad spectrum
once diagnosis known use a narrow spectrum antibiotic.
Treatment for MRSA
Flucloxacillin
Treatment for streptococcus pyogenes
Benzylpenicillin
Treatment for anaerobes
Metronidazole
3 Reasons for combining antibiotics
to increase efficacy
to provide adequately broad spectrum
To reduce risk of resistance.
treatment for gram +ves
vancomycin
treatment for gram -ves
cephlosporins
Treatment of bacteria is dependent on
concentration at the site of action
right amount of concentration
time
