Antibiotics Flashcards
What are the factors influencing infection?
Virulence, number of organisms and host resistance
Host resistance can be local (cleaning, closure, contraction-ability for organism to enter host) or systemic (disease or drug suppressing immune system).
What are the drug characteristics that must be taken into consideration during antimicrobial agent selection?
Lipid solubility (more means better lung penetration), molecular weight and protein binding (less means more efficient diffusion, more means longer half life)
What would affect the route of administration of an antibiotic?
Oral for mild infections that can be treated on an outpatient basis
Intravenous for more serious infections
Intramuscular for rapid action
Topical for infections on the skin surface
What would the choice of empiric therapy depend on?
Site of infection (polymicrobial), immunocompromised, neutropenia (low levels of neutrophils), age (very young or old), hospital acquired infection
What are antibiotics used for?
Prophylaxis (surgery, rheumatic fever, meninges, endocarditis), therapy and suppression
How can we identify the infecting organism?
Culture and identification, gram stain, antigen detection, DNA or RNA detection and immune response.
What does it mean to be bactericidal?
Kill bacteria at concentrations achievable in the patient
What does it mean to be bacteriostatic?
Arrest the growth and replication of organisms, limiting the spread of infection.
What is minimum inhibitory concentration (MIC)?
The lowest concentration of drug that inhibits bacterial growth. For clinical therapy, antibiotic concentration must be greater than MIC.
What is minimum bactericidal concentration (MBC)?
Minimum concentration of antibiotic that kills bacteria (99.9% fewer bacteria after 24 hours)
What is concentration-dependent killing?
A significant increase in the rate of bacterial killing with higher concentrations of the drug.
Useful for rapid killing
What is time-dependent killing?
Drugs that require time to achieve effective killing. Higher concentrations of drug do not increase rate of killing
What is the post-antibiotic effect?
The suppression of microbial growth even after levels of antibiotic have fallen below MIC. Length of time following removal of antimicrobial drug to reach log-phase growth.
What are narrow spectrum antibiotics? Give an example.
Antibiotics that act on a limited group of microorganisms.
Isoniazid on mycobacteria
What are extended spectrum antibiotics? Give an example.
Antibiotics that are effective against one class of organisms as well as a significant number in a different class. Ampicillin in gram + bacilli and gram - rods
What are broad spectrum antibiotics? Give an example.
Antibiotics that act to kill a range of antimicrobial species.
When are antibiotic combinations used?
When there is an unknown organism, polymicrobial infection, to achieve antibiotic synergy or when there are patient/population factors
Why would antibiotic combinations be used?
What is known in the hospital and dose related toxicity.
What are some disadvantages of antibiotic combinations?
Superinfection, eradication of normal microflora, resistance, adverse effects (greater toxicity), patient adherence to therapy and increased cost
What is drug synergism?
When the effect of two drugs in combination is greater than the sum of the effect when two drugs are administered independently.
Enhancing uptake of other, enhancing metabolic effect of other, inhibit same target in different ways, inhibit targets in different pathways
What is drug antagonism?
When the effects of two drugs in combination is less than the sum of the effect when two drugs are administered independently.
What type of testing is the checkerboard method?
Bacteriostatic because the bacteria has not yet grown.
What type of testing is the disk diffusion method?
Bactercidal because it is killing off the bacteria that has already grown.
What are gram positive bacteria?
Have a thick outer cell wall composed of peptidoglycans. Purple in gram stain
Staph. aureus
What are gram negative bacteria?
Have an outer membrane containing lipopolysaccharides and a thin inner peptidoglycan cell wall. Pink in gram stain
E. coli
How does a gram stain work?
Crystal violet, iodine, decolorizer (alcohol or acetone) and safarin red
What are examples of cell wall inhibitors?
Penicillins and cephalosporins
How do cell wall inhibitors work?
Only effective against actively growing bacteria. Beta-lactam ring inhibits transpeptidases that form cross links between peptidoglycan chains essential for cell wall integrity. Creates osmotic pressure on cells, resulting in cell lysis. Autolysins from gram + bacteria can damage cell.
What are the types of penicillins?
Penicillin G (original), penicillin V
Penicillinase-resistant penicillins (methicillin, cloxacillin)
Extended spectrum penicillins (ampicillin, amoxicillin)
Bactericidal, cross resistance, cross allergic potential
What is the administration route of antibiotics determined by?
The stability of the medication to gastric acid and the severity of infection.
How are penicillins absorbed?
Most are incompletely absorbed so they affect the composition of the intestinal flora
Must be administered before a meal or 2-3 hours after.
How are penicillins distributed in the body?
Throughout the body, crosses the placenta but doesn’t penetrate bone or CNS
What are some adverse effects of penicillins?
GI effects (lessened due to microflora)
Allergy, cross allergy within penicillin class
Reduced coagulation
No teratogenicity
What are some examples of cephalosporins?
Cephalexin, Cephalothin, Cepazolin, Cefepin (similar mechanism and structure to penicillins)
How are cephalosporins distributed?
Throughout the body
cefazolin penetrates bone, cefuroxime crosses BBB, cefotaxime penetrates cerebrospinal fluid
What are the adverse effects/problems with cephalosporins?
Cross resistance and cross allergic potential with each other and other penicillins
Allergy and GI effects less common than penicillins
What is vancomycin? How does it work?
A tricyclic glycopeptide that binds to D-Ala-D-Ala side chain of the precursor pentapeptide and prevents transglycosylation step in peptidoglycan polymerization
What are some adverse effects of vancomycin?
Fever, chills or phlebitis
Rapid infusion causes shock due to histamine release
Hearing loss in patients with kidney disease
Toxicity when given with aminoglycosides
How do protein synthesis inhibitors work?
Bind to the 70S ribosomes (only found in bacteria and composed of 50S and 30S subunits, 80S are in bacteria) and stop the synthesis of protein
What are protein synthesis inhibitors effective against?
Gram positive and gram negative bacteria as well as other microorganisms
What are some examples of protein synthesis inhibitors?
Tetracyclines (doxycycline, minocycline), chloramphenicol, aminoglycosides (gentamicin, streptomycin), macrolides (clarithromycin, azithromycin), clindamycin, erythromycin
How do tetracyclines work?
Bind irreversibly to the 30S ribosome subunit and blocks acyl-tRNA access to the ribosome.
Broad spectrum, bacteriostatic
How are tetracyclines absorbed?
Adequately but incompletely absorbed orally.
Reduced by dairy foods and antacids
What are the adverse effects of tetracyclines?
GI discomfort (take with food) Deposition in bones and teeth of children, sunburn, dizziness, nausea, headache, superinfections (resistance is common)