Antimicrobial Principles Flashcards
What factors (6) influence the antimicrobial agent chosen?
identity of organism, susceptibility, site of infection, patient factors, safety, cost
How do you identify the organism?
culture, gram stain, detection of antigens or nucleic acids, or host inflammatory response– culture must be preformed prior to treatment
As optometrists, drug choice is determined by:
site of infection and patient’s medical history… broad spectrum antibiotic is usually chosen
What is bacteriostatic?
arrest the growth and replication of bacteria and let body’s immune system eliminate the infection
What is bactericidal?
drugs kill bacteria, more aggressive and often used for seriously ill patients
What is MIC?
minimum inhibitory concentration- lowest concentration of an antibiotic that inhibits bacterial growth, must reach this level clinically to have an effect
What is MBC?
minimum bactericidal concentration- lowest concentration of antibiotic that kills the bacteria
What three things are entry to the CNS influenced by?
lipid solubility, molecular weight, and protein binding
What are some patient factors that can affect the immune system?
alcoholism, diabetes, HIV, malnutrition, autoimmune disease, pregnancy, age, immunosuppressive drugs
What are the 5 major patient factors for drug selection?
renal function, hepatic function, poor perfusion, age, and pregnancy
What happens if kidney function is poor?
accumulation of antibiotics
What is an example of an antibiotic among the least toxic of all drugs?
penicillin
What is an example of an antibiotic with serious potential for toxicity?
chloramphenicol
What administration is preferred for mild infections and outpatient treatment?
oral
Sometimes antibiotics are so poorly absorbed from GI….
they must have parenteral administration
What is rational dosing based on?
pharmacodynamics (relationship of concentration to effect) and pharmacokinetics (ADME)
What three properties have significant influence on rational dosing?
concentration-dependent killing, time-dependent killing, post antibiotic effect
What is concentration-dependent killing?
certain agents show significant increase in the rate of bacterial killing as the concentration of antibiotic increases (favor once a day bolus infusion) ex: aminoglycosides
What is time-dependent killing?
effect is best predicted by the percentage of time that blood concentrations remain above MIC– favor extended or continuous infusions exL b-lactam, macrolides
What is PAE?
post antibiotic effect– persistent suppression of microbial growth that occurs after antibiotic levels have fallen bellow the MIC
How does a long PAE affect dosing?
only requires one dose a day ex: aminoglycosides and fluoroquinolones
What are the six major families of antibiotics?
penicillins, cephalosporins, tetracyclines, aminoglycosides, macrolides, and fluoroquinolones
What is a narrow-spectrum antibiotic?
act on only a single or limited group of microorganisms
What is an extended spectrum antibiotic?
effective against gram (+) and a significant amount of gram (-)
What is a broad spectrum antibiotic?
affect a wide variety of microbial species and can alter normal flora
Describe gram (+) organisms
surrounded by peptidoglycan cell wall (85% of eye infections) ex: Staph epidermis and aureus on the skin and strep pneumonia or streptococcus
Describe gram (-) organisms
cell wall is surrounded by outer membrane. pores prohibit entry of many antibiotics because they need to be hydrophilic to pass through the pores
What are the four groups of gram (-) organisms?
enterics, haemophilus influenza, neisseria and pseudomonas
What organism is a cause of eye infections in adults?
staph aureus
What organisms is a cause of eye infections in children and old peope?
haemophilus influenza
Describe anaerobic infections
usually composed of mixed gram + and - bacteria, infections occur when bacteria invade poorly oxygenated tissues or tissues that are normally sterile– encased in abscess wall and are foul smelling
In general should you select one drug or a combination?
one best agent
Why is it best to choose a single agent to treat in infection in most cases?
reduces possibility of superinfection, decreases resistance, minimizes toxicity
What is resistance?
bacteria are resistant if the maximal level of the antibiotic that can be tolerated by the host does not halt the bacteria growth
Resistance can be either ___ or _____
natural or developed
What are the two ways resistance are developed?
genetic alterations and altered expression of proteins
What are spontaneous mutations?
insertion, deletion, or substitution alterations in the chromosomal DNA– may be lethal to the cell but if not the mutation will be passed to the progeny
What is DNA transfer of resistance?
one bacterium may transfer resistance to another by plasmid
What are three results of altered expression of proteins?
modification of target sites, decreased accumulation, enzymatic inactivation
What does modification of a target site do?
a change in structure to an antibiotic binding site may produce resistance, often from a mutation
What does decreased accumulation do?
decreased uptake or increased efflux do not allow the drug to gain access to the site of action of an organism
What does enzymatic inactivation do?
some bacteria can destroy or inactivate the antimicrobial agent
What are prophylactic antibiotics?
use of antibiotics for prevention rather than treatment– should be restricted to situations where the benefits outweigh the potential risks because it can result in resistance
What is an example of prophylactic treatment that optometrists might use?
treatment prior to surgical procedures like cataract surgery
T/F since antibiotics are selectively toxic to an invading organism, the host will not have any adverse effects
false, still susceptible to adverse effects
What are two major complications or antibiotics?
direct toxicity and superinfections
What is direct toxicity?
high concentrations of antibiotics can directly affect host cellular processes ex: aminoglycosides and ototoxicity
What are superinfections?
alterations in the normal microbial flora that permits overgrowth and the subsequent infections are difficult to treat ex: yeast infection after antibiotics
