antibiotics laurale dyner md pediatric infectious disease fellow march 2009
TRANSCRIPT
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ANTIBIOTICSLauraLe Dyner MD
Pediatric Infectious Disease FellowMarch 2009
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PREP Question
A 14-year-old boy with a h/o CF is admitted with a pulmonary exacerbation. His sputum grows Pseudomonas. What is the most appropriate therapy (+ an aminoglycoside)? A. Ampicillin B. Ceftriaxone C. Cefuroxime D. Pipericillin E. Vancomycin
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PREP Question
A 10-year-old boy with a h/o short gut syndrome has coagulase-negative Staph bacteremia. What is the most appropriate antibiotic therapy? A. Cephalothin B. Clindamycin C. Nafcillin D. Penicillin G E. Vancomycin
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PREP Question
Of the following, the greatest advantage of using a 3rd generation cephalosporin over an aminoglycoside, is a lower rate of: A. Hypersensitivity reactions B. Nephrotoxicity C. Pseudomembraneous colitis D. Thrombocytopenia E. Thrombophlebitis
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PREP Question
A 2-year-old girl develops meningococcal meningitis. Family members are prescribed rifampin.What medication may be less effective when taking rifampin? A. Amoxicillin B. Furosemide C. Oral contraceptives D. Ranitidine E. Salicylates
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History of Antibiotics
Molds were used in ancient cultures 1880s: Search for antibiotics began after acceptance
of the germ theory 1929: The mold penicillium was found to inhibit
bacterial growth of Staph aureus 1935: Synthetic antimicrobial were discovered
(sulfonamides) 1942: Penicillin G Procaine was manufactured & sold 1940s-1960s: Natural antibiotics (streptomycin,
chloramphenicol, tetracycline, etc) were discovered
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Microbial Sources
of Antibiotics
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Classes of Antibiotics
Spectrum of Activity Gram-positives Gram-negatives Anaerobes Atypicals Mycobacteria
Chemical structure Mechanism of Action
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1944
1948
1947
1950
1955
1955
1959
1962
1962
1963
20001985
19901940
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Choice of Antibiotics Identify the infecting organism Evaluate drug sensitivity
Antibiotogram Specific sensitivities of the organism
Target the site of infection Drug safety/side effect profile
Selective toxicity: drugs that kill microorganisms but do not affect the host
DRUG INTERACTIONS Patient factors
Age Genetic or metabolic abnormalities Renal or hepatic function
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Mechanism of Action
Bacteria have their own enzymes for: Cell wall formation Protein synthesis DNA replication RNA synthesis Synthesis of essential metabolites
Antibiotics target these sites
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Minimal Inhibitory Concentration (MIC) Lowest concentration of antimicrobial that
inhibits the growth of the organism after an 18 to 24 hour incubation period
Interpreted in relation to the specific antibiotic and achievable drug levels
Can not compare MICs between different antibiotics
Discrepancies between in vitro and in vivo
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MIC
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Time Above MIC
Effectiveness of beta-lactams, macrolides, clindamycin, & linezolid is optimal when the concentration of the antibiotics exceeds the MIC of the organism for > 40% of the dosing interval at the site of the infection
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Concentration Dependent Killing Effectiveness of fluoroquinolones and
aminoglycosides is greatest when peak levels of the drug are high Peak/MIC ratios of > 8 Supports the idea of daily aminoglycoside dosing
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Inhibitors of Cell Wall Synthesis
Penicillins Penicillin G Aminopenicillins Penicillinase-resistant Anti-pseudomonal Cephalosporins
Monobactams Carbapenems Bacitracin Vancomycin Isoniazid Ethambutol
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Beta-Lactams
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Beta-Lactams
Bactericidal Inhibits synthesis of
the mucopeptides in the cell wall of multiplying bacteria
Cell wall defects lead to lysis & death
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Penicillins Derived from the fungus Penicillum Therapeutic concentrations in most tissues
Poor CSF penetration Renal excretion
Side effects Hypersensitivity (5% cross react with
cephalosporins), nephritis, neurotoxicity, platelet dysfunction
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Penicillins
Structure
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Natural Penicillins
Active against Strep, some Staph, Enterococcus, Neisseria, Actinomyces, Listeria, Treponema
Bacteriocidal Binds to & competitively inhibits the
transpeptidase enzyme Cell wall synthesis is arrested Susceptible to penicillinase (beta-lactamase) Side effects: hypersensitivity/anaphylaxis
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Aminopenicillins Ampicillin & amoxicillin Effective against Strep, Enterococcus Better penetration through the outer membranes of
gram-negative bacteria & better binding to transpeptidase
Offer better coverage of gram-negative bacteria H. influenza, Moraxella, E.coli, Proteus, Salmonella
First line therapy for otitis media/sinusitis Still inhibited by penicillinase, therefore less
effective against Staph
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Aminopenicillins
Side effects: rash with mononucleosis infection
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Semi-synthetic Penicillins
Penicillinase-resistant penicillins Monobactams Carbapenems Extended-spectrum penicillins Penicillins + beta-lactamase inhibitors
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Penicillinase-Resistant Penicillins Methicillin, nafcillin, oxacillin, cloxacillin,
dicloxacillin
Gram-positive bacteria, particularly Staph No activity against gram-negatives These are the drugs of choice for Staph
aureus when it is resistant to penicillin Natural penicillins are more efficacious if the
organism is penicillin sensitive
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Anti-Pseudomonal Penicillins Ureidopenicillins (piperacillin & mezlocillin)
Good gram-positive and gram-negative coverage Including Pseudomonas & Citrobacter
Carboxypenicillins (ticarcillin & carbenicillin) Less gram-positive coverage & more gram-
negative coverage Pseudomonas, Proteus, E. coli, Enterobacter,
Serratia, Salmonella, Shigella Often used with aminoglycosides
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Beta-Lactamase Inhibitors
Clavulanic acid, sulbactam, tazobactam Enzymes that inhibit beta-lactamase Clavulanic acid irreversibly binds beta-lactamase
Given in combination with penicillins Augmentin = amoxicillin + clavulanic acid Timentin = timentin + clavulanic acid Unasyn = ampicillin + sulbactam Zosyn = piperacillin + tazobactam
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Cephalosporins Semisynthetic beta-lactams Beta-lactam ring that is more resistant to beta-lactamase New R-group side chain: leads to drugs with different
spectrums of activity Cover a broad spectrum of gram-positive and negative
organisms
Cephalosporinases Enterococci and MRSA are resistant to cephalosporins As the generation increases, penetration into the CSF
increases Side effects: 5-10% cross-reactivity with penicillins
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Cephalosporins Cefazolin
Cefuroxime
Ceftriaxone
Cefepime
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Cephalosporin Generations
1st generation Cefadroxil (Duricef) Cephalexin (Keflex) Cefazolin (Kefzol)
2nd generation Cefaclor (Ceclor) Cefuroxime (Ceftin)
Cefotetan Cefoxitin (Mefoxin)
3rd Generation Ceftriaxone (Rocephin) Cefotaxime (Claforan) Cefdinir (Omnicef) Cefixime (Suprax)
Ceftazidime (Fortaz)
4th Generation Cefepime (Maxipime)
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Cephalosporin Generations 1st
2nd
3rd
4th
Strep, Staph, E. coli, Klebsiella, Proteus Surgical ppx
H. influenza, Moraxella, E. coli, Enterobacter, etc Not as effective against S. aureus as 1st gen.
Gram negative> gram positive Ceftriaxone: useful against meningitis Ceftazidime is active against Pseudomonas
Active against MSSA, Strep, aerobic gram negatives including Pseudomonas
No Enterococcus or anaerobic coverage
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Monobactams
Aztreonam Beta-lactamase resistant Has the beta-lactam ring with side groups
attached to the ring. Narrow spectrum of activity: only binds to the
transpeptidase of gram-negative bacteria Pseudomonas, E.coli, Klebsiella, Proteus Ineffective against gram-positives & anaerobes
Can use in penicillin allergic patients
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Carbapenems Meropenem Imipenem Ertapenem
Broadest spectrum beta-lactam Activity against gram-negatives, gram-positives,
anaerobes MSSA, Strep, Pseudomonas, Proteus, Klebsiella, Bacteroides
Resistance in MRSA, some Pseudomonas, Mycoplasma
Imipenem lowers the seizure threshold Side effects: some PCN allergy cross-reactivity
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Vancomycin Covers nearly all gram-positive organisms
MRSA, coagulase-negative Staph, Enterococcus, highly resistant Strep pneumo
Leuconostoc resistant Glycopeptide (Streptomyces orientalis) Inhibits synthesis of cell wall phospholipids &
prevents cross-linking of peptidoglycans at an earlier step than beta-lactams
Also inhibits RNA synthesis Synergy with aminoglycosides
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Vancomycin Not absorbed orally! Poor CSF penetration Not the drug of choice for MSSA
Delayed sterilization of blood infections Drug levels
Peak = Toxicity (goal 25-40) Trough = Efficacy (5-15) Goal is to achieve drug levels above the MIC
Side effects: “red man syndrome”, neutropenia, renal and ototoxicity, phlebitis, fever, chills
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Vancomycin
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Protein Synthesis Inhibitors
Chloramphenicol, clindamycin, macrolides, aminoglycosides, tetracyclines
Bacterial cells depend on the continued production of proteins for growth and survival
Targets the bacterial ribosome Bacterial – 70S (50S/30S) Human – 80S (60S/40S)
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Bacterial Ribosome 70S Particle 50S subunit (large)
Chloramphenicol Lincosamides
(Clindamycin) Oxazolidindones
(Linezolid) Macrolides
30S subunit (small) Tetracycline Aminoglycosides
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Lincosamides
Clindamycin Gram-positive organisms & anaerobes Inhibits protein synthesis by irreversibly binding to the
50S subunit
Poor CSF penetration Good PO bioavailability Side effects: C. difficile (pseudomembraneous colitis)
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Oxazolidinones
Linezolid Broad gram-positive coverage (MRSA & VRE) Prevents the formation of the 70S initiation complex
of bacterial protein synthesis by binding to the 50S subunit at the interface with 30S subunit.
Bacteriostatic Treatment of gram-positives including VRE & MRSA Good PO bioavailability Side effects: bone marrow suppression, lactic
acidosis, headache, GI upset
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Macrolides Irreversibly bind the 50S subunit Inhibits peptide bond formation Erythromycin
Gram positives: MSSA, Strep, Bordetella, Treponema Atypicals: Mycoplasma, Chlamydia, Ureaplasma
Clarithromycin Similar to Erythromycin Increased activity against gram negatives (H. influenza,
Moraxella) Azithromycin
Decreased activity against gram positives Increased activity against H. influenza & Moraxella
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Macrolides Azithromycin structure
Side Effects Oxidized by cytochrome P450
Leads to increased serum concentrations of theophylline, coumadin, digoxin, cyclosporin, etc.
Erythromycin GI symptoms
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Tetracyclines
Tetracycline, doxycycline Bacteriostatic; Binds the 30S subunit Spirochetes, Mycoplasma, Chlamydia, some gram-
positives & gram-negatives Can chelate with milk products, Ca, & Mg
Side effects: phototoxic dermatitis, discolored teeth, renal & hepatic toxicity
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Aminoglycosides Streptomycin, gentamicin, tobramycin, amikacin Binds to the 30S subunit, disrupting protein synthesis Active against aerobic gram-negative organisms
E. coli, Proteus, Serratia, Klebsiella, Pseudomonas Synergism for gram positive organisms with cell wall
inhibitors because it leads to increased permeability of the cell
Side effects: CN VIII toxicity (hearing loss, vertigo), renal toxicity, neuromuscular blockade Patients also on vancomycin are at higher risk of ototoxicity
and nephrotoxicity
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Aminoglycosides
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Aminoglycosides
Concentration dependent due to active transport for uptake
Significant post-antibiotic effect
Drug levels Peak = efficacy Trough = toxicity (<2)
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Inhibitors of Metabolism
Septra/Bactrim Bacteria must synthesize folate to form cofactors for
purines, pyrimidines, and amino acid synthesis Gram-positives (including some MRSA), enteric
gram negatives, Pneumocystis jiroveci, H. influenza, Strep pneumo, Stenotrophomonas, Nocardia
Sulfomethoxazole & TMP act synergistically Side effects: bone marrow suppression, anemia in
those with G6PD deficiency, rashes (photodermatitis; can lead to TEN)
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Trimethoprim (TMP)
Dihydrofolate reductase inhibitor Mimics dihydrofolate reductase of bacteria &
competitively inhibits the reduction of folate into its active form, tetrahydrofolate (TH4)
Inhibiting bacterial DNA formation
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Sulfonamides
Sulfamethoxazole, sulfasoxazole Bacteriostatic Inhibit bacterial folic acid synthesis by
competitively inhibiting para amino benzoic acid (PABA)
Good penetration including CSF
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Inhibitors of Nucleic Acid Synthesis & Function
Fluoroquinolones Rifampin
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Fluoroquinolones Ciprofloxacin, ofloxacin, levofloxacin, moxifloxacin Synthetic derivative of nalidixic acid Effective against gram positives and negatives,
atypicals, Pseudomonas (cipro) Decreased activity against anaerobes
Inhibit DNA gyrase, resulting in permanent DNA cleavage (bacteriocidal)
Concentration dependent killing Great PO bioavailability Wide distribution: CSF, saliva, bone/cartilage Side effects: headache, nausea; damage cartilage
in animals, Achilles tendonitis & rupture
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Fluoroquinolones
Ciprofloxacin Pseudomonas, H. influenza, Moraxella Resistance in MRSA, Strep pneumo & pyogenes Ciprofloxacin can inhibit GABA and cause seizures
Levofloxacin (Respiratory) Strep, S. aureus (MRSA), H. influenza, atypicals Levofloxacin & moxifloxacin have increased Staph
coverage, including ciprofloxacin resistant strains Used for otitis media, sinusitis, & pneumonia
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Rifampin
Interacts with the bacterial DNA-dependent RNA polymerase, inhibiting RNA synthesis
Mycobacterium, gram positives & negatives Treats the carrier state in H. influenza and
meningococcus Resistance develops rapidly May induce the cytochrome P450 system
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Conclusion
Target antibiotic use for the patient and the organism you are treating
Know side effect profiles Always check your antibiotic dosing and drug
interactions
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Questions & Comments
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Resources
Hayley Gans MD & Kathleen Gutierrez, “Antibiotics Overview” 2006
Prober, Long, & Pickering. Principles & Practice of Pediatric Infectious Disease, 3rd Edition
Centers for Disease Control UpToDate 2007 The 2006 American Academy of Pediatrics Redbook PREP American Academy of Pediatrics Questions
1999-2006