Antibiotics Flashcards
What are the 9 major antibiotic categories?
- beta-lactams?
- macrolides and clindamycin
- tetracyclines/glycylcyclines
- glycopeptides
- aminoglycosides
- quinolones
- sulfonamides and trimethoprim
- metronidazole
- linezolid
What is the mechanism of action of penicillins?
penicillins bind to penicillin-binding protein on the pathogen and inhibit peptidoglycan synthesis. Breaks the cell wall and prevents its production and repair
Are penicillins bactericidal or bacteriostatic
bactericidal
What forms of resistance have organisms developed against penicillins
- production of beta-lactamases – break the ring before it can bind
- lack of or altered PBPs
- efflux of drug out of cell
- failure to synthesize peptidoglycans such as mycoplasma or metabolically inactive bacteria
What id the parenteral form of natural penicillin
Penicillin G
what types of bacteria is penicillin G active against
gram positive bacteria and spirochetes (syphilis)
Why can’t penicillin G be used orally?
highly acid labile and would be destroyed by stomach acid before it could absorb
What forms of Pen G are available
- procaine pen G
- benzathine pen G (IM injection only)
What is penicillin V
the oral formulation of penicillin G. It is more acid stable but must be taken on an empty stomach
What kinds of infections are pen G and V used for
- Drug of choice for streptococci, pneumococci, meningococci, spirochetes, clostridia, anaeobic gp rods, and actinomyces
- also effective against enterococci which are very hard to kill
what kind of penicillins are methicillin/cloxacillin?
isoxazolyl penicillins
What bacteria were methicillin/cloxacillin designed for?
Staphylococcus aureus –> gram positive
What are the other drugs in the methicillin/cloxacillin family?
flucloxacillin and dicloxacillin
Does methicillin have activity against all gram positive bacterias
No, the activity is specifically against staph aureus
Can we use methicillin/cloxacillin for to treat MRSA?
No, MRSA is the only staph aureus infection that won’t be treated by these medications
What are aminopenicillins active against?
both gram positive and gram negative organisms
What are the two drugs in the aminopenicillin category and what are their forms?
- Ampicillin: used IV, not taken orally because dosing would have to be frequent. More acid stable than natural pens but they have poor bioavailability
- Amoxicillin: used orally, better absorption than ampicillin because more acid stable, also available combined with clavulanic acid to inhibit beta-lactamases
Which bacterial infections do we use aminopenicillins for?
- streptococci
- enterococci
- neiserria
- non-beta lactamase producing H. influenzae
- E. coli
- p. mirabilis
- Salmonella
Which drug is in the ureidopenicillin class?
piperacillin
What kind of activity do ureidopenicillins possess?
They have increased activity against gram negative rods, specifically Pseudomonas aeruginosa, which is very pathogenic
How can piperacillin be administrated?
Parenteral (IV) only
In what situations are ureidopenicillins (piperacillin) used?
only used in hospital, reserved for very sick patients and not seen in community pharmacy
What beta lactamase inhibitor can be combined with piperacillin
tazobactam
Describe the pharmacokinetics of all penicillins
- oral bioavailabilities varies across classes
- distributed widely to the tissues and to the CNS
- most penicillins are excreted by the kidney
What is specific about amoxicillin and administration compared to other penicillins
amoxicillin is the only penicillin taken with food
What are the half-lives of penicillins?
- short
- penicillin dosing is frequent
- cloxacillin is QID, the rest are mostly TID
Are penicillins concentration dependent or independent, and what does this mean
Concentration independent:
- once a certain threshold of blood levels is reached, there is no more added killing potential
- goal of therapy is to keep the blood levels above the threshold for the whole duration of therapy
- most easily done with an IV drip, which is unrealistic and inconvenient
What is a drug interaction with penicillins
oral contraceptives:
penicillins destruct the estrogens and prevent the enterohepatic recirculation
What are the adverse effects of penicillins
- allergic reactions – anaphylaxis if severe
- serum sickness
- skin rash
- fever, nephritic, eosinophilia
- seizures, encephalopathy, delirium
- electrolyte imbalances
- neutropenia, thrombocytopenia
- diarrhea, gi upset (most common)
Does the mechanism of action of cephalosporins differ from that of penicillins?
No, MOA of cephalosporins is the same. beta lactam ring binds to PBR on the pathogen and breaks the cell wall
