Saturday, April 12, 2008

Antibiotics made EZ

Whether you are studying for your NCLEX or USMLE examination, or you are a practicing nurse or physician, the first step in understanding antibiotic drugs, is to know about the bugs you are trying to kill. We will take a two blog look at this subject, first by summarizing the bacteria that we frequently encounter in the hospital.

First lets take a broad look at bacteria:

Gram Positive CocciSTAPHYLOCOCCUS sp.

•Gram Positive Rods
CLOSTRIDIUM (anaerobes)

Gram Negative Cocci

–BACTEROIDES (anaerobes)

Atypical Bacteria: Think Doxy!
–CHLAMYDIA (intracellular)
–MYCOPLASMA (no cell wall)
–SPIROCHETES (curves: Syphillis)
–BORRELA (Corkscrews: Lyme)
Think INH/Rifampin/Azithro
–MYCOBACTER (Acid fast: TB, Leprosy, M.Avium Complex)

Gram Positive Cocci

Staph aureus (coagulase positive)
•Most pathogenic of the staphs; toxins cause Toxic Shock, Scalded Skin, Gastroenteritis
•Cause skin infections, Pneumonia (nosocomial), Endocarditis, OsteomyelitisAbscess formation common; Can initiate clotting (think DIC)
•Tx: Oxacillin family; (Vancomycin if MRSA; Zyvox if VRSA; Bactrim or Doxy if Community MRSA)
–Also susceptible to: 1/2/4 Gen Cephs, Carbapenems, Macrolides
MRSA: Staph resistant to Oxacillins and most other drugs; Use Vanco, Zyvox, or Synercid

Staph epidermidis (coagulase negative)
•Normal flora of human skin
•Causes infection in immuno-compromised or depressed patients often via Central lines
•Tx: Similar to Staph Aureus (Vanco if MRSE, Zyvox if VRSE)

Alpha HemolyticStrep pneumoniae (Pneumococcus): Leading cause of Pneumonia, Otitis Media, and Meningitis
Strep viridans: Normal flora of mouth, can cause Dental abscess and Endocarditis

Beta Hemolytic
•Group A (Strep pyogenes): Strep throat, Rheumatic fever, Scarlet fever, Glomulerulonephritis, Necrotizing fasciitis•Group B (Strep agalactiae): Can colonize vagina and cause Meningitis or Pneumonia in newborn
–Tx: PCN G; (Quinolone if PCN resistant; Ceftriaxone if in brain)
•Also susceptible to: 1/2/4 Cephs, Macrolides, AminoPCNs, Vancomycin, Quinolones

•Common nosocomial infection with multi-drug resistance
•Cause Sepsis, Cellulitis, Intraabdominal infx, Endocarditis, UTI
•Tx: Ampicillin (or Vancomycin) + Gentamycin; (Zyvox or Synercid if VRE)
–Only other effective drugs: Zosyn, Imipenem, and Quinolones

Gram Positive Rods

–Commonly reside in soil, sewage, and stream water but rarely cause disease; If the immune response is slow, however, they move into cells and then are missed by immune cells
–Cause of Listeriosis, a lethal food bourne illness with mortality rate of 25%; Can invade CNS
–Tx: Ampicillin (often with Gentamicin)

•Cornybacterium diptheriae
–Toxin producing (2nd most lethal toxin to humans) causes Pharyngitis w/heart/CNS damage
–Tx: Antitoxin + PCN (Erythromycin if PCN allergic)

•Bacillus anthracis
–This anaerobic bacteria is the cause of Anthrax (meaning Coal = large black lesions)
–Lives in soil, and can be ingested by grazing animals where it causes rapid death (is then possible to inhale or ingest the bacteria from dead animals)
–Tx: PCN; (Cipro or Doxycycline if PCN allergic)

•Clostridium (anaerobic species)
C. difficile
•Overgrowth in gut after Antibiotic treatment (Clindamycin, 3/4 Gen Cephs, Amp/Amox), causes Pseudomembranous Colitis•Tx: PO Metronidazole (or PO Vancomycin if relapse after taking Metro)
–C. tetani
•Toxin producing (3rd most lethal toxin to humans) causes PNS blockade (Tetany, Seizure, Death)
•Tx: Toxin irreversible once bound, so rapid treatment with PCN or Metronidazole imperative
–C. botulinum
•Toxin producing (Most lethal toxin to humans; 500 g could kill the entire world) that causes Botulism (a nerve blockade disease that leads to rapid paralysis and death)
•Bacteria can not survive in high oxygen or acidic environment, so usually ingesting bacteria not fatal as they are killed rapidly in GI tract; Must ingest toxins to have effects
•Infants (pre solid food) have a less acidic GI tract, so things harboring this bacteria (honey) can deliver the organism, which is then allowed to grow in more basic pH GI tract
•Tx: Hardy bacteria are not killed by antibiotics; Antitoxin very hard to find so Mechanical Ventilation and removal of cause (i.e. vomiting or debridement of wound) usually only thing possible

Gram Negative Cocci

Neisseria meningitidis (aka Meningococcus)
–Common cause of meningitis; Also Meningococcemia (a rapidly fatal sepsis that kills over 50% of effected infants) and DIC
–Tx: PCN G (Ceftriaxone if PCN allergic) ; Best treatment is prevention with vaccine

Neisseria gonorrhea–Cause of the STD Gonorrhea, as well as Conjunctivitis in newborn of infected mom
–Tx: Ceftriaxone (or Ciprofloxacin) and Azithromycin for possible concurrent Chlamydia

•Moraxella catarrhalis
–Causes URI and Otitis Media, as well as Pneumonia in smokers; Also COPD exacerbations
–Tx: Augmentin and Erythromycin
•Also susceptible to 2/3 Gen Cephs, Quinolones, Bactrim

Gram Negative Rods

A very common bug to recognize during your NCLEX or USMLE studying. It is useful to divide this class into the usual medical pathologies caused by each

•Urinary pathogens

–E. coli
•Normal intestinal flora cause 90% of UTI; Also Pyelonephritis
•Pathogenic varieties are not normal flora and can cause Infectious diarrhea, Hemolytic Anemia
•Tx: Ciprofloxacin or Bactrim (Zosyn also effective)

•Causes UTI, in addition to renal calculi (struvite, CaCO3)
•Tx: Levaquin or Bactrim (Often treated without knowing you are treating Proteus)

Respiratory pathogens

Haemophilus influenzae

•Cause: Pneumonia, AOM; Also Sepsis, Meningitis, Cellulitis
•Tx: Azithromycin
–Also susceptible to po 3/4 Gen Cephs, Augmentin, Doxycycline, Quinolones, Carbapenems
Klebsiella pneumoniae
•Usually only pathogenic in hospitalized immunocompromised causing Pneumonia and/or Sepsis
•Rapid resitance develops, especially against Cephalosporins and Quinolones
•S/S: Profuse, Jelly-like, Bloody sputum and high mortality rate
•Tx: Carbapenems or Zosyn

–LegionellaPneumonia, derived airborn from water ducts, air conditioning units, water towers
•Tx: Macrolide (or Quinolone or Doxycycline)

Pseudomonas aeruginosa
•Opportunistic infection causes Pneumonia, Sepsis, UTI, Right side Endocarditis, Osteomyelitis in Diabetic foot ulcers•First s/s often overwhelming Gram negative sepsis; 2nd most common cause of infection in ICU
•Extremely resistant to many drugs; All effective drugs IV, except Cipro and Levaquin so their use is severely restricted to avoid development of resistant strains
•Tx: Ceftazidime and Gentamycin (or Imipenem or Zosyn- varies widely between hospitals)
–Also susceptible to the following: Tobramycin, Cefipime, Colistin, Aztreonam

Pneumonia, Sepsis, Shock common, Up to 70% mortality; Can live 3 weeks on dry surface
•Tx: Imipenem
–Colistin or Doxycycline is alternative

Gastrointestinal pathogens

Helicobacter Pylori

•Common cause of Peptic Ulcer Disease
•Tx: (CAP) Clarithromycin, Amoxicillin, PPI (proton pump inhibitor)

•Common cause of Diarrhea; Some forms also cause Typhoid or Sepsis
Ciprofloxacin (rule out C.Dif with any infectious diarrhea)

•Causes bloody, purulent diarrhea in nursing homes and preschools
•Tx: Ciprofloxacin

Vibrio Cholera
•Causes rice water diarrhea, with death from dehydration
•Tx: Doxycycline, fluids and electrolytes

–Yersenia•One form causes diarrhea; Another form causes Bubonic Plague
•Tx: Gentamicin

•GNR and Sepsis: Notes of Interest
–Many GNR have endotoxins, which are actually components of their cell wall
•When antibiotics begin their destruction, these toxins are released into the bloodstream in massive quantities, leading to Sepsis (Massive immune response) and eventually Septic Shock (Low BP and organ dysfunction)
•For this reason, Bacteremia (bugs in blood) with GNR is among the most serious of diseases, and should be treated aggresively in an ICU
•With Shock and 2 organs dysfunctioning the mortality rate is over 40%; With each additional organ dysfunction add 15%
Sepsis is the #1 killer in the ICU, but is more preventable than you would think; The dirty source, is more often than not, indwelling catheters, so take extreme care with hygiene if you are ICU bound!!!


Nursing Resource said...

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ilham said...
This comment has been removed by the author.
ilham said...

Really a very interesting article!!i mean i m studying medicine n i think it will help me a lot to rmember all that really thank you