Test 5: Antibiotics (Bacteria) Flashcards
What is Gram Staining?
The first step in the identification of a bacterial organism.
-Staining with crystal violet dye differentiates bacteria by the chemical and physical properties of their cell walls by detecting peptidoglycan
-Peptidoglycan: present in a thick layer in gram-positive bacteria
-Not all bacteria can be classified by this technique - some are gram variable
What is the response to gram-positive vs gram-negative bacteria to gram staining?
Gram-positive bacteria retain the crystal violet dye
Gram-negative bacteria stain a red or pink coloring 2/2 a counterstain (commonly safranin or fuchsine)
What is a Culture & Sensitivity?
Culture: Identifying the organism
Sensitivity: Identify the susceptibility/resistance of the bacteria to the selected ABX (which agent will kill it)
Especially important with Gram (-) due to the high incidence of drug-resistant organisms
What must be intact for antibiotics to work?
The acquired immune system.
-Effectiveness of antibiotic therapy may depend on acquired immune responses
Why does scheduling and time intervals matter with antibiotics?
Compliance with proper time intervals maintains the MEC/MIC (minimum effective/inhibitory concentration).
What does it mean if an organism is Susceptible?
Requires a low or moderate MIC/MEC that can be attained by giving usual doses of an ABX.
What does it mean if an organism is Resistant?
Requires a high MIC/MEC, and may require higher concentrations of drugs than can be achieved in the body even with large doses.
-Can be due to over use of inappropriately prescribed ABXs (ex: prescribing abx for a viral infection)
-Ex: MRSA, VRE
What are International Units (IU)?
-Unit of measurement for the amount of a substance
-The mass or volume that constitutes one international unit varies based on which substance is being measured
-Variance is based on the biological activity or effect for the purpose of easier comparison across substances
-Used to quantify vitamins, hormones, some medications, vaccines, blood products, and similar biologically active substances.
What are the general pharmacokinetics of Antibiotics?
Absorption:
-Oral bioavailability greater than 70% for most antibiotics
IV route preferred route for treatment of serious infections
Distribution:
-Varies based on agent and location of infection
Metabolism:
-Varies
-Hepatic vs excreted unchanged in kidneys
Elimination:
-All routes: renal, EHC, lactation
What is the usual duration of therapy for acute infections?
Average 7-10 days, or until the patient is asymptomatic/afebrile for 48-72 hours (after initial therapy is completed)
-If initial therapy doesn’t work, need to switch to a different ABX. Continue therapy for 48-72 hrs afebrile.
What is unique about the Sulfonamides?
-They are lipid soluble to be able to enter the tissues, but then are biotransformed to water soluble and stay in the urinary system. Good for UTIs.
-Sulfa allergies can be an issue in generic form of propofol (issue in someone with sulfa allergy and pt with asthma).
-Preservative in generic propofol called sodium metabisulfite. Concern for cross allergy with sulfa.
What are the 4 Mechanisms of Action for antibiotics?
1) Inhibitors of folic acid and nucleotide biosynthesis
-Sulfonamides
2) Bacterial Cell wall synthesis inhibitors
-PCN
-Cephalosporins
-Vancomycin
-Aztreonam
3) Inhibitors of DNA replication & RNA synthesis
-Quinolones
-Rifampin
4) Protein Synthesis Inhibitors:
-Tetracycline
-Aminoglycosides
-Microlides
-Isoniazid
What hypersensitivity reaction can occur with antibiotics?
Usually Type 1.
-Skin rash to Anaphylaxis.
-IgE mediated
How do superinfections occur?
Antibiotics kill normal body flora, making room for opportunistic infections.
-C. Diff
-Thrush
What are common organ toxicities associated with antibiotics?
-Ototoxicity
-Nephrotoxicity
-Cardiotoxicity
-Neurotoxicity (seizures)
-Hemolytic anemias
What are common drug interactions that occur with Antibiotics?
-Vancomycin + Furosemide/ASA = increased ototoxicity
-Cephalosporins interfere with ethanol metabolism
-Tetracyclines reduce the effectiveness of oral contraceptives
-Really any ABX can reduce effectiveness of oral contraceptives for 7-10 days.
What are the S/sx associated with true anaphylaxis?
-Angioedema (throat/oral swelling)
-Bronchoconstriction (can’t breathe)
-itchy rash/pruritus (central itching - more than just a local spot)
What are normal host defenses?
-Intact skin (primary mechanism of defense)
-Mucous membranes
-Anti-infective secretions
-Mechanical movements
-Phagocytic cells
-Immune & inflammatory processes
What are threats to normal host defenses that increase the risk of infection?
-Breaks in the skin & mucous membranes
-Impaired blood supply
-Neutropenia & other blood disorders
-Poor personal hygiene
-Suppression of normal bacteria
-Suppression of the immune & inflammatory response (chemo, steroids)
-DM & chronic autoimmune diseases
-Advanced age (Renal function peaks at age 35)
What should be initial laboratory therapy?
-Provider prescribes a drug that is likely to be effective for immediate admin
-Based on the estimate of the most likely pathogen from assessment of signs & symptoms and Site of infection
-Broad spectrum antibiotic or a combination of drugs
-Most laboratory tests to ID an organism take 48 to 72 hours (Except for gram stain and rapid strep test)
What are the results from a culture report?
Gram (+)
Gram (-)
Anaerobic
Mixed
What are provider responsibilities in prescribing antibiotics?
-Knowledge of ABX resistance patterns in the community and agency
-Knowledge of organisms most likely to infect particular body tissues (Ex: E.Coli often responsible for UTI’s)
-Drug’s ability to penetrate infected tissues: Many ABX are renally excreted and therefore effective against UTI’s.
-There are limits to treating infections within the brain, eyes, gallbladder or prostate (Difficult for drugs to reach effective concentrations in these tissues)
Drug’s toxicity and risk to benefit ratio
-Least toxic drug with the greatest effect should be used
-Cost: Least expensive drug that is likely to be effective
How are antibiotics used perioperatively?
Perioperative Antibiotic Prophylaxis
-Single dose prior to surgery (trying to get MEC in the tissue directly surrounding surgical site). Timing and tourniquet use are barriers to getting it to target tissue.
-Provides effective tissue concentration during the procedure
-Contamination? Treatment continues after the procedure is complete
-Agent: Pathogen most likely to colonize the operative area (ex: Skin is probably staph)
-Usually Cefazolin (activity against staph aureus or Strep)
When do you repeat perioperative antibiotics?
From the time of initial dose not from the time of incision!
-For longer procedures (ex: Cefazolin is q 4 hours)
-Procedures involving insertion of prosthetic materials
-Contaminated or infected operative sites: Contaminated surgeries (abscess), Traumatic wounds (open fractures), Ruptured viscera (ruptured appendix)
-Recommended after 1500ml EBL
