Antibiotic Principles Flashcards
What is the difference between Bactericidal drugs and Bacteriostatic?
When should one be used over the other?
Bactericidal drugs are those that kill the infection outright. These should be used when the immune system is compromised and cannot fight the infection itself.
Bacteriostatic drugs are those that simply slow down the infection and should be used when the immune system is working fine.
Define the following and when you would use them:
- Prophylactic treatment
- Empiric treatment
- Definitive treatment
Prophylaxis: If a patient is at high risk of aquiring an infection we give them an antibiotic before a possible infection can get out of hand.
- Ex. someone with a prosthetic hip can easily have a bacterial infection that takes place on the metal piece. So we give them an antibiotic before they go to the dentist/surgery to prevent from easy infection.
- Use Broad or at least extended treatment for this
Empiric treatment: The patient obviously has an full fledged infection but we don’t know the identity of the infection yet.
- Common with C. diff: We get an infection that is really bad and can’t wait to be treated
- Remember to take a culture FIRST BEFORE GIVING THE DRUG!!!! You still need to identify what the person has.
- Use Broad treatment for this
Definitive treatment: We have cultured the infection and know what the bacteria/virus/fungal infection is. You can now be specific in your treatment.
-Use narrow spectrum treatment for this.
What should you be thinking about before writing a prescription?
- ) How can you minimize antibacterial resistance
- ) How can you minimize harm/ what harm is going to happen to your patient with this drug
- ) How can you make the treatment cost effective? (25-30% of hospital budget goes to antibacterials)
- ) Remember to get a culture and identify the microbe BEFORE you prescribe.
What blood tests can you use to identify that it is a microbial/bacterial infection?
- CBC (Complete Blood Count differential)
+ Look for - C-reactive Protein
+This is non-specific but will be elevated if there is a bacterial infection, inflammation, or acute injury - White Blood Cell (WBC) count
+This is specific: Different infections will result in elevation of different WBCs
+Elevated Neutrophils = Acute Bacterial infection or acute inflammation
+Elevated Eosinophiles = Allergic reaction, Parasites, Drug reactions, Malignancies
+Elevated Basophiles = Chronic Myeloid Leukemia
+Elevated Monocytes = Chronic infections (Bacterial)
+Elevated Lymphocytes = Viral Infections, Chronic immune stimulation
What are some tests to identify what specific microbe is causing the infection?
- Rapid Antigen Detection Test:
+This is a test that is looking for antigens that are specific to the microbe that is causing the infection.
+This can give a false positive so be sure to make a cell culture too! - Group A antigen testing to test for Strep. in patients with sore throats (pharyngitis)
- Gram Stain
+Those that are Gram + will have a purple stain becuase the indigo dye will bind more readily to their thick peptidoglycan walls- These are usually cocci (spheres)
+Those that are Gram - will have a pink stain because the indigo dye will not stay inside their thin peptidoglycan walls - These are usually bacili (rods)
- These are usually cocci (spheres)
-Biochemical tests to differentiate between Staph (clumps) or Strep (chain links):
+Catalase test: Monitors degradation of H2O2 to tell whether the growth is Staphylococci or streptococci
- Staph will grown, Strep will not
+Coagulase Test: Allows you to tell what staphylococcus strains are there
+Hemolysis: Clearing around idfferent cultures on a blood agar plate to show different streptococci strains
- Alpha-Hemolysis: Makes green ring - Beta-Hemolysis: Forms clearing around colonies - Gamma-Hemolysis: No clearing
-Arterial glucose/lactose fermentation
What is the Minimum Inhibitory Concentration?
Why is it important for drug efficacy?
The minimum dosage needed to inhibit a target organism.
-It is important because the longer a drug stays at its MIC, the more effective it will be.
-These can be found in the Clinical and Laboratory Standards Institute (CLSI)
What are some key things to think about when choosing a drug for a patient?
-Dosage Vs Timing
+ Is it better to give a low dose over a longer time span or high dose at once?
-Status of the patient’s immune system
-Pharmacokinetics: The effect a patient’s body will have on a drug
+ Right Drug, Dosage, Route, and Duration
+ What is the absorption of the drug into the vascular system like? Distribution to target? Metabolism?
+ Condition of the patient’s liver (what is metabolizing the drug) and kidneys (excreting the drug)
- Distribution: Is there tissue necrosis or an abscess at the target (well vascularized or not?)
- Age
- Other diseases? Liver disease could limit the metabolism of the drug
-Patient taking other medications?
+ Broad spec drugs can combine to create a super infection, or other drugs can cancel each other out
+ Consider giving a probiotic
-Toxicity: Vancomycin –> histamine release –> Red Man Syndrome
-Genetic factors: G6P mutation –> poor management of oxidative stress
+ Sulfonamides and Metronadiazole create lots of oxidative stress!
-Pregnant?
What is a super infection?
This is when your normal flora of bacteria are wiped out but the infectious bacteria is not, allowing the pathogenic bacteria to use all the resources it normally would have had to compete for! It is allowed to flourish!
What is intrinsic resistance?
What is acquired resistance?
Intrinsic: Resistance that a bacteria receives without changing its genes
Acquired resistance: Bacteria change their genes via lysogenic virus, plasmid, or sex pilli \+ this can happen through: - Transduction - Transformation - Conjugation
What are three mechanisms for drug resistance? (not asking about acquiring new genes, just speaking broadly about how a bacteria survives an antibiotic)
- Prevent a drug from reaching its target (cell wall, capsule, glycogen matrix, etc.)
- Drug is deactivated (Penicillinase that cuts the beta-lactam ring)
- Change target (can change the ribosomal RNA that a drug would normally bind to)
If a patient is listed as having an allergy to a drug does that mean you should never try to give them that drug or something like it?
No, sometimes people have a bad reaction but won’t another time. Do a skin test to see if they will react badly again.
What is Antibiotic Susceptibility Testing, and how can it be useful?
Antibiotic Susceptibility Testing is a test that is done to see how well a specific antibiotic works against a specific bacteria. This can be very useful in making sure that the drug you prescribe will actually work.
- If an empirical prescription is not working, review this to be sure you are prescribing the right AB.
- You should know the etiology of the infection (know what bacteria it is) otherwise the test could be misleading.
What are the advantages to combination drug therapy?
What are some drawbacks?
Advantages:
- Increase spectrum of the treatment
- Faster treatment
- Increase effectiveness
- Can target multiple locations of infections (CNS and skin infection will require two different drugs)
- Prevent drug resistance by ensuring that the bacteria are killed
Drawbacks:
- Increased risk of toxicity
- Antagonism: The drugs can cancel each other out!
- Can increase AB resistance by selecting for microorganisms that are resistant to treatment
- Superinfection
- Extra cost
What are some important toxicities associated with antibiotics?
- Seizures: Beta-lactams (esp. Carbapenems)
- Hepatotoxicity: Rifampin (damage to liver); it can induce drug metabolizing enzymes –> increased drug metabolism
-Nephrotoxicitiy: Sulfonamides, Aminoglycosides, Vanco (Kidney damage)
+ Clarithromycin and Erythromycin can inhibit hepatic metabolism
- Ototoxicity: Aminoglycosides Vanco (Ear damage)
- QTc interval prolongation: Macrolides, Fluoroquinolones
- Anemia: Chloramphenicol, Trimethoprim
- Arthralgia: Quinupristin/dalfopristin, Fluoroquinolones
- Disulfiram Reaction when taken with Alcohol (crazy hangover): Metronidazole, 2nd Gen. Cephalosporins with methylthiotetrazole groups
- Superinfection: Clindamycin, Fluoroquinolones, 3rd Gen. Cephalosporin, Ampicillin
What two drugs should not be used with newborns (birth - 28 days)
- )Chloramphenicol because children can’t glucuronidate this (add a glucose to it so it can be excreted)
- ) Erythromycin because of pyloric stenosis (narrowing of the opening of the stomach)
