Infectious Diseases Flashcards
Antimicrobial selection
- Clinical diagnosis
- Obtain cultures/specimens
- Microbial diagnosis based on most likely organism or culture/test result
- Select appropriate medication
- May need to change drug based on culture/sensitivity test results
Empiric therapy:
treatment of an infection before specific culture information has been reported or obtained
Definitive therapy:
antibiotic therapy tailored to treat organism identified with cultures
Prophylactic therapy:
treatment with antibiotics to prevent an infection
Inhibit Cell Wall Synthesis
Beta-lactams [Penicillins (+/- Beta-lactamase inhibitors); Cephalosporins (3 generations); Monobactams; Carbapenems]
Glycopeptides
Fosfomycin
Inhibit Protein Synthesis
Aminoglycosides Ansamycins
Tetracyclines Glycylcyclines
Macrolides & Ketolides Oxazolidinones
Lincosamides Phenicols
Streptogramins
Inhibit Membrane Functions
Leptopeptides
Polymyxin
Anti-metabolites
Sulfonamides
Inhibit Nucleic Acid Synthesis
Fluoroquinolones
Furanes
Beta-lactams
Penicillins Cephalosporins (3 generations) Monobactams Carbapenems Glycopeptides Fosfomycin All antibiotics in this category contain a beta lactam ring that is essential for activity, but is also susceptible to hydrolysis by beta-lactamases, destroying the antimicrobial action of the compound. Beta-lactamase-producing staphylococci cause about 80% of community-acquired staph infections.
Penicillins
Inhibit the biosynthesis of peptidoglycan bacterial cell wall
Well-absorbed from GI tract, but several are unstable in acid
Bound to proteins, therefore have good distribution to most tissues
Small amount is metabolized, most excreted as unchanged drug in the urine.
Natural penicillins:
Streptococcus, some Enterococcus strains, some non-penicillinase-producing Staphlococcus
Aminopenicillins
Greater activity against gram-negative bacteria due to enhanced ability to penetrate the outer membrane organisms
Used for gram-negative urinary and gastrointestinal (GI) pathogens E. coli, Proteus mirabilis, Salmonella, some Shigella species, and Enterococcus faecalis; active against the common gram-negative respiratory pathogens Moraxella catarrhalis (and Haemophilus influenzae type B)
Aminopenicillins have a broader spectrum
Combination with beta-lactamase inhibitors to broaden their spectrum:
Clavulanate, sulbactam, tazobactam
Amoxicillin/clavulanate (Augmentin) combination is an antibiotic that belongs to the group of medicines known as penicillins and beta-lactamase inhibitors. It works by killing the bacteria and preventing their growth.
Probenecid
Gout medication =
Prolongs the half-life of PCNs and cephalosporins and increases risk for toxicity.
If a patient has a failed amoxicillin course
If a patient has a failed amoxicillin course and the infection does not resolve or recurs within a few weeks, you would then order Amoxicillin-clavulanate (to add the beta-lactamse inhibitor).
Amoxicillin is the antibiotic of choice unless the child received it within the previous 30 days, has concurrent purulent conjunctivitis, or is allergic to penicillin; in these cases, clinicians should prescribe an antibiotic with additional β-lactamase coverage.
Amoxicillin is first-line therapy
For acute otitis media (AOM), pharyngitis, and sinusitis.
Penicillin (PCN) is first-line therapy
For streptococcal pharyngitis & syphilis.
Amoxicillin/clavulanate (Augmentin) is first-line therapy
For infection following bites, including human.
Additional uses of PCNs
Sinusitis is treated with a penicillin if the mucopurulent drainage and cough have not improved after 10 days. Pneumonia, STIs, UTI, and Wound Infections
Endocarditis prophylaxis
Helicobacter pylori
Lyme Disease
Clinical Uses of Beta-Lactamase Inhibitor
Human and animal bites Aspiration pneumonia Foot infections in diabetic patients Sinusitis Resistant otitis media Lung abscess Does not cover MRSA
Piperacillin and tazobactam(Zosyn):
About as broad as you can get
Adverse drug reactions (ADRs) of PCNs
May cause serious immediate allergic reactions. Reactions occur within 2 to 30 minutes of administration.
Patients may be given desensitization therapy.
Rash: maculopapular rash occurs 9% of time that is not allergic in origin, appears 7 to 10 days into treatment.
GI: diarrhea, nausea/vomiting (n/v), addition of clavulanate increases risk of diarrhea
Fungal overgrowth
C. difficile colitis
Most are pregnancy category B.
Anaphylactic shock Type I
Most serious, urticaria, pruritus.
Anaphylactic shock Type II
Hemolytic anemia, neutropenia (nafcillin), thrombocytopenia.
Anaphylactic shock Type III
Serum sickness (rare-urticaria, fever joint swelling, angioneuroticedema, pruritus, bronchospasm-7-12 days after), interstitial nephritis(methicillin).
Anaphylactic shock Type IV
Contact dermatitis.
Sinusitis Common Pathogens
Strict criteria: persistent, not improving for at least 10 days. Common pathogens S. pneumoniae: 30% H. flu: 20% Moraxella catarrhalis: 20% Rarely, Staphylococcus
Antibiotic Choices for Sinusitis
Amoxicillin first line:
80 to 90 mg/kg/day in high-risk children;
45 mg/kg/day in low-risk children
Adults: 500 mg three times/day, or high-dose Augmentin
Antibiotic Choices for Sinusitis for penicillin-allergic patients
Children: cefdinir, cefuroxime, or cefpodoxime
Adults: doxycycline or respiratory fluoroquinolone (levofloxacin)
Sinusitis: If started on Augmentin & worsening symptoms:
Children: consider cefdinir, cefuroxime, cefpodoxime
Adults: consider respiratory fluoroquinolone (levofloxacin).
Cephalosporin pharmacodynamics
Structurally and chemically similar to PCNs
Inhibit mucopeptide synthesis in the bacterial cell wall. Bactericidal
All cephalosporins penetrate poorly into ICF and the vitreous humor.
Cephalosporins First Generation
Cefazolin (Ancef), Cephalexin (Keflex), Cefadroxil
Used for gram positive skin and soft tissue infections
Primarily active against gram-positive bacteria, S. aureus and S. epidermidis
Cephalosporins Second Generation
Cefuroxime (Ceftin), Cefaclor
Active against same as first generation, plus Klebsiella, Proteus, E. coli
Cephalosporins Third Generation
Ceftriaxone, Cefotaxime, Ceftazidime
Used for broader indications
More active against gram-negative bacteria; Does not cover MRSA; Treats community acquired bacterial meningitis
Cephalosporins Fourth Generation
Cefepime (Maxipime)
Resistant to beta-lactamase
Primarily active against gram-positive bacteria
Four generations of cephalosporins
Progression from 1st to 4th reflects an increase in gram – coverage and loss of gram + cover.
Cephalosporin pharmacokinetics
Oral formulations absorbed from GI tract
Widely distributed to most tissues
Some highly bound to proteins
Some are metabolized to less active compounds, most excreted via kidneys, as unchanged drug
