Antibiotics 1 Flashcards
host factors to consider
age, weight, organ function,signs and symptoms of infection, immune status, comorbid conditions, foreign bodies, living environment, travel, drug allergies, prior antibiotics
organism factors to consider
intrinsic resistance, propensity to acquire resistance during treatment, prior exposure to antibiotics, likelihood of organism being pathogenic, minimum inhibitory concentration (MIC), likelihood of infectious agent growing in culture
antimicrobial factors to consider
antimicrobial spectrum, clinical data, pharmacokinetics, synergy or antagonism with other agents, drug interactions, convenience, cost
gram negative organisms cell structure and function
outer membrane of LPS endotoxin, outer membrane proteins for attachment and virulence, porin protein-passive transport, thin cell wall, B lactamase in the periplasmic space
gram positive organisms cell structure and function
thick cell wall composed of NAM and NAG alternating. Cross linked by transpeptidase. Beta lactamase secreted outside the cell.
beta lactam mechanism of action
bind to penicillin-binding proteins. These proteins catalyze the polymerization of the glycan strand and cross linking between glycan chains.
mechanisms of resistance to beta lactam drugs
enzymatic destruction: beta lactamase (big deal in gram negative organisms)
reduced permeability: gram negative organisms can alter porin channels to limit entry
target site alteration: gram positive organisms can have low affinity binding of antibiotic to target PBPs
spectrum of activity for beta lactam drugs
lack activity against atypical organisms like mycoplasma pneumoniae, and chlamydophilia pneumoniae. lack activity against MRSA except for ceftaroline.
pharmacokinetics of beta lactam drugs
short half lives, 20 minutes to a few hours. widely distributed, CSF penetration variable. Liver metabolism. Renal excretion, but ceftriaxone is hepatobiliary.
time dependent killing and beta lactam drugs
bacterial killing is achieved when these drugs acylate PBPs. antibacterial effect requires a certain number of PBPs to be acylated to cause stasis or cidality. give more frequently and give as a continuous infusion. Want concentration > MIC for ~50% of the dosing interval.
side effects of beta lactam drugs
hypersensitivity reactions: anaphylaxis is rare, delayed hypersens can happen along with drug fever and acute interstitial nephritis. Seizures can happen with high doses in patients with renal dysfunction. Can cause N/V and diarrhea
natural penicillins spectrum
mostly gram-positive aerobic organisms. Streptococci, enterococcus. Can deal with oral anaerobes and clostridium, but not C. difficile. Can deal with gram negatives like N. meningitidis, as well as spirochetes like T. pallidum (syphilis). Is drug of choice for syphilis
natural penicillins clinical uses
odontogenic infections. streptococcal infections (pharyngitis, cellulitis, endocarditis, pneumococcal pneumonia). enterococcal infections. Syphilis.
natural penicillins pharmacokinetics
penicillin V is more acid stable than penicillin G, leading to better bioavailability. Widely distributed, renal elimination.
natural penicillin pharmacodynamics
T>MIC. can be given as continuous infusion to increase T > MIC and allow outpatient administration
anti-staphylococcal penicillin agents
oxacillin, nafcillin, dicloxacillin
anti-staphylococcal penicillin spectrum
MSSA (methicillin-susceptible Staphylococcus aureus) and streptococci
anti-staphylococcal penicillin clinical uses
primarily MSSA infection. can be used for skin and soft tissue infection, joint infection, bacteremia, and endocarditis. Superior to vancomycin for MSSA infection.
anti-staphylococcal penicillin adverse events
oxacillin: hepatotoxicity, neutropenia. Nafcillin: similar to oxacillin, but also have thrombophlebitis
anti-staph penicillin pharmacokinetics
dicloxacillin: 50% absorbed, decreased with food.
Oxacillin, nafcillin: 30 min half life, requires frequent dosing
aminopenicillin agents
ampicillin, amoxicillin
spectrum for aminopenicillins
similar to penicillin. ampicillin is a drug of choice for enterococci. used in listeria. Poor activity in enterobacteriaceae due to beta lactamases. combining with a B-lactamase inhibitor restores some susceptibility. Active against non B-lactamase producing haemophilus