Antimicrobials Flashcards
what is minimal inhibitory concentration (MIC)
lowest concentration of an antibiotic that prevents visible growth of the bacteria –> used in calculating an effective clinical dose
clinical dose should be greater than MIC
what is minimal bactericidal growth (MBC)
lowest concentration of an antibiotic that results in no growth
compare the MIC and MBC in a true bactericidal agent
MBC would be equal to just slight higher than the MIC
what is a disadvantage of using combination therapy
some agents only work on multiplying bacteria so if using an agent that causes bacteriostasis, it would be less effective
what do gram positive and gram negative stain as in what are the colors
Gram pos has thick peptidoglycan - stains purple
Gram neg has thin peptidoglycan - stains pink
what are some important factors that help in selecting the right agent to treat an infection
- Identity of organism
- Empiric therapy
- effect of site of infection on therapy
- patient factors
- safety of the agent
- cost of therapy
- route of administration
factors that affect if drug can gain access to BBB
- the more lipid soluble it is, the easier to cross BBB
- the larger the drug, the less likely it is to cross BBB
- if bound to plasma proteins, less free drug so less likely to gain access to BBB
mechanisms in which resistance can be acquired
- spontaneous mutation of DNA
- DNA transfer of drug resistance
- altered expression of proteins in drug-resistant organisms
what are some complications of antimicrobials
- hypersensitivity very common: from urticaria to anaphylactic shock
- direct toxicity when the antimicrobial affects the host’s cellular processes
- superinfections: secondary infection develops while treating primary infection
how are the antimicrobials divided in terms of class
- cell wall synthesis inhibitors
- protein synthesis inhibitors
- drugs that affect nucleic acid synthesis
- miscellaneous and urinary antiseptics
what are the cell wall synthesis inhibitors
- Beta Lactams antibiotics: penicillins, cephalosporins, carbapenems, monobactams
- Vancomycin
- Daptomycin
- Bacitracin
- Fosfomycin
what is an overall benefit of using cell wall synthesis inhibitors
mammalian cells do not have cell walls so specifically toxic to bacteria
what is an overall disadvantage of using cell wall synthesis
requires actively dividing cells so cell wall synthesis must be occurring in order for it to be inhibited
mechanism of action of beta lactams
bactericidal enzymes that bind and inactivate enzymes like penicillin binding proteins (PBPs) involved in final stage of cell wall synthesis –> cell lysis
what are the three mechanisms of bacterial resistance to the beta lactams
- decreased penetration to the target site
- alteration of target site
- inactivation of the antibiotic by a bacterial enyzme
how do bacteria decrease the penetration of beta lactams to the target site
- gram neg bacteria have a outer wall that is an effective barrier against beta lactam antibiotics hence antibiotics must use hydrophilic porin to gain access to the PBP (penicillin binding protein)
- bacteria like pseudomonas do not have porins to gain access hence resistant to antibiotic
- gram pos bacteria have cell wall that is easily penetrable and do not require presence of porins
what bacterial enzyme do they use to inactivate beta lactams
some bacteria such as staph and gram neg bacteria have beta lactamases that inactivate beta lactams
what can be given in addition to beta lactams to inhibit the beta lactamase activity of bacteria
(name the beta lactams)
beta lactams: penicillin, cephalosporin, carbapenems, and monobactams
beta lactam inhibitors: CAST
Clauvulanic Acid
Sulbactam
Tazobactam
name the penicillins
ADOPT N-MAC
Amoxicillin Dicloxacillin Oxacillin Penicillin G Penicillin G benzathine Penicillin G procaine Penicillin V Piperacillin Ticarcillin
Nafcillin
Methicillin
Ampicillin
Carbenicillin
what is Penicillin G active against
- gram pos cocci (except b-lactamase producing staph, penicillin resistant pneumococci, enterococci, MRSA)
- gram pos rods like listeria and clostridium perfringens
- gram neg cocci like neisseria (except b-lactamase producing neisseria)
- most anerobes (except bacteriodes)
- spirochetes like Treponema Pallidum
Penicillin G is drug of choice for what condition
Syphilis (benzathine penicillin)
Strep infections (esp to prevent rheumatic fever)
susceptible pneumococci
what is Penicillin V mainly used for
oropharyngeal infections like strep throat
what are the anti-staph penicillin and their importance
MOND
Methicillin
Oxacillin
Nafcillin
Dicloxacillin
they inhibit b-lactamase producing staph (except MRSA) –> used for staph infections
what are the extended spectrum penicillin and what are the organisms they are fight against
Amoxicillin and Ampicillin HHELPSSS kill enterococci
H. Influenza H. pylori E. coli Listeria Proteus mirabilis Strep pneumonia Shigella Salmonella Enterococci
