Prunuske: Antibiotic Discussion Flashcards
A 8-year-old child had a sore throat, difficulty swallowing, and fever for 5 days. Examination was remarkable for fever; and an extensive red rash on the neck, groin, armpit. A bright red lingual papillae superimposed on a white coat, exudative tonsillitis and cervical lymphadenopathy. The mother is asking for an antibiotic.
What is your differential?
Group A Streptococcus Corynebacterium diphtheriae- grey pseudomembrane Mycoplasma pneumoniae Coronavirus Influenza Rhinovirus Epstein-Barr Virus Coxsackie virus
What causes most pharyngitis/URI? How do we treat them?
Viruses
DO NOT GIVE AN ANTIBACTERIAL DRUG
What factors in presentation suggest infection is bacterial in nature?
A centor scor of 2 or 3:
Absence of cough= 1 3-14 = 1 14-45 = 0 >45 = -1 Anterior cervical lymphadenoaphy = 1 Fever = 1 Tonsillar erythema/exudates = 1
What do you do if a centor score is 2 or 3?
Conduct a rapid antigen detection test (recognizes C carbohydrate)
What is the specificity and sensitivity for a positive rapid antigen detection test?
Specificity (>95%) (SPin) but sensitivity is (80%) (SNout)
What does a lower sensitivity mean?
People will have the disease bon’t DONT test positive
What does a high specificity mean?
If you test positive you can be fairly confident that the pt streptoccous in their throats but they may be asymptomtic carriers
What is the gold standard for treatment if a pt has a centor score of 2 or three and a negative rapid antigen detection test?
Take a culture
A patients throat culture shows a gram + cocci in chains that is also beta hemolytic. What is it?
S. Pyogenes
What are the virulence factors for s. pyogenes?
M protein and hyaluronic capsule prevent phagocytosis, invasins and toxins are also secreted
Why do we treat s. pyogenes?
Treatment prevents sequelae, alleviates symptoms, and decreases spread.
What sequaela are associated w/ s. pyogenes?
RF Glomerulonephritis Hemorrhagic cystitis Scarlet Fever Skin infection
Which of the following were more likely to prescribe early antibiotics without a positive culture?
Men Family Physicians, Practicing more than 12 yrs, Rural
*more likely to get antibiotics on a Friday
What is the appropriate antibiotic treatment for Group A strep infections?
Penicillin
What is the MOA of Penicillin?
Cell wall inhibitor (our cells don’t have cell walls so the med isn’t toxic)
Penicillins, cephalosporins, carbapenems, aztreonams are all what?
Beta lactams
What do beta lactams do?
Bind to PENCILLIN BINDING PROTEINS which are TRANSPEPTIDASES required for cell wall synthesis.
This leads to a BUILD UP of cell wall precursors that activates autolytic enzymes.
What beta lactams bactericidal or bacteriostatic?
bactericidal
When would you consider using penicillin G over Penicillin V?
G is single dose in clinic where as oral form needs to be taken 2-3 times a day for ten days.
Amoxicillin is a BIG gun and could also kill normal flora, so it’s not your first choice.
You give the patient an IM injection of penicillin G. Five minutes later she is in respiratory distress with audible wheezing. Her skin is mottled and cool. She is tachycardic and her blood pressure has fallen. What do you do?
Administer a subcutaneous injection of epinephrine
What is a major side effect associated w/ betalactams?
Anaphylactic reaction
What affect does epi have on a pt’s vascular system?
vasooconstriction> increased in bp
Which adrenoceptor primarily mediates the vascular response?
alpha 1
What effect will epinephrine have on her respiratory system?
bronchodilation
Which adrenoceptor primarily mediates the respiratory system response?
beta 2
What do you use to treat less severe allergic reactions to penicillin?
antihistamines
corticosteroids
What should you avoid if a pt is hypersensitive to penicillin?
avoid other penicillin-subclasses and if severe avoid cephalosporins and carbapenems
What drug is safe to use in pts w/ penicillin allergies but is not a good choice for treating s. pharyngitis?
Aztreonam
That drug is only affective against gram - organisms and we have a gram + organism
Erythromycin, Azithromycin, Clarithromycin are all….
macrolides!
What is the MOA of a macrolide?
Binds 23S rRNA of 50S subunit inhibiting translocation
What is the spectrum of a macrolide?
broad coverage of respiratory pathogenes
What causes resistance to macrolides?
methylation of 23S rRNA where drug is binding so it can’t bind anymore
binding site and increased efflux
What adverse affects are associated w/ macrolides?
GI discomfort, Prolonged QT interval, Hepatic failure- inhibits CYP3A4,
What macrolide is associated w/ miscarriages?
Clarithromycin
Treatment failure occurs in 15% of positive GAS cases so you reculture and switch therapy. What might be some causes of treatment failure?
- Antibiotic resistance- rare for penicillin, 5-8% of strains are resistant to macrolides
- Lack of compliance- patient feels better after 3-4 days and doesn’t finish 10 day course
- Had viral pharyngitis but was a carrier for GAS
- Neighboring flora like Haemophilus influenzae can secrete beta-lactamases
- Streptococcus pyogenes can enter epithelial cells
In December, a 73-year-old man from a nursing home was brought to the hospital in acute respiratory distress. He had been in his usual state of health until 10AM the previous day when he suddenly developed fever, chills, muscle aches, cough, and prostration. Several other nursing home residents had developed a similar illness during the previous week. His past history is unremarkable and he had not seen a physician in the past year.
Rapid Influenza test comes back positive. How do you approach the treatment?
Generally supportive treatment
Treat with antivirals if:
severe illness,
> 65 years,
What are two influenza antivirals?
Adamantane (only active against influenza A)
Neuraminidase (oseltamivir= tamiflu, zanamivir)
Are influenza antivirals active against a dividing virus?
Yes if you treat early (<48 hrs)
What is a preferred influenza prophylaxis?
Vaccine
Antivirals work but SE are common b/c treatment is longer than therapy
What blocks uncoating of the influenza virus once it has entered the cell?
Amantadine
Rimantadine
What blocks the release of influenza from a cell?
Neuraminidase inhibitors
Why is resistance to adamantanes extremely high?
change in viral M2 proton ion channel
Why is resistance to neuraminidases currenly low?
change in viral hemaglutinin or neuraminidase
Why are rates of mutation in influenza so high?
Mutation rate is HIGH for RNA virus
Antigenic SHIFT and DRIFT
What causes new strains of influenza?
Antigenic shift and drift
What is antigenic shift?
gene reassortment leading to altered surface proteins and antigenic profile
What causes antigenic drift?
small gene mutations/changes leading to altered Ab binding sites and escape from immunity
What does a neuraminidase inhibitor do?
prevents viral release
What are two types of neuraminidase inhibitors?
- Oseltamivir: ALL AGES
> 1yr, oral prodrug activated by HEPATIC ESTERASES
Renal excretion- modify for renal insufficiency
GI side effects, headache, fatigue - Zanamivir
> 7yrs, poor oral bioavailability
inhaled 10-20% reaches lung don’t use if other airway diseases
remainder of drug in oropharynx can cause bronchospasms
avoid in patients with asthma and pulmonary disease
A 73 year old man presented with a 7-day history of cough and high fever, in the month of January. He had a flu-like illness 1 week prior to this episode but had otherwise maintained good health. A chest x-ray revealed alveolar infiltrate in the posterior segment of the left lower lobe.
Secondary bacterial pneumonia
What is a superinfection?
secondary infection occurring after previous infection
What causes a secondary infection?
Induce by broad spectrum antibiotic killing off normal flora