Antimicrobials Flashcards
Define postantibiotic effect.
Killing action of microorganisms continues once drug plasma levels have fallen below a measurable level.
Define minimal inhibitory concentration (MIC).
Lowest concentration of antibiotic that prevents visible growth. Usually measured y broth/tube dilution or disk sensitivity
Define minimal bactericidal concentration (MBC).
Lowest concentration of antibiotics that result in a 99.9% decline in colony count after overnight broth dilution incubations. The MBC of a truly bactericidal agent is equal to or just slightly above its MIC value.
Define empiric therapy.
Tx without known exact microorganism due to time sensitive pathology (ex. meningitis). Choice of drug is influenced by site of infection or patients history. Frequently, broad spectrum therapy is used in the initial tx of serious infections.
General complications of Abx therapy?
- hypersensitivity
- direct toxicity
- superinfection - new or secondary infection that occurs during antimicrobial therapy of primary infection
Basic features of Penicillin.
Bactericidal, inhibits last step in peptidoglycan synthesis by binding to penicillin-binding protein [bacterial enzyme that penicillin binds to inactivate replication]. Binding to PBP is determined by the size, charge and hydrophobicity of the penicillin Abx. [PCN can easily cross cell wall of Gram positive bacteria, but use porins within gram-negative bacteria making it more selective] PBP mutations can lead to Abx resistance. Because these drugs target the peptidoglycan synthesis, they are only active against organisms with peptidoglycan cell walls [they are INEFFECTIVE against mycoplasma, protozoa, fungi, viruses]. Bacteria also produce autolysin to mediate cell lysis - Penicillins activate autolysins initiating cell death.
Half-life = 30-60 minutes (except repository PCNs which have a long effect)
Oral absorption - impaired by food, except amoxicillin which has high oral bioavailability and Nafcillin which is erratic so is not suitable for oral admin
Nafcillin, Ampicillin, peperacillin - high levels in bile
Poor CSF penetration and insufficiency levels in prostate and eye.
PCN excretion - via kidneys so do not administer to pt with kidney failure
Oxacillin and dicloxacillin - renal and biliary excretion
Nafcillin - primary excretion in bile
Penicillin G?
Penicillin G = Benzylpenicillin
Natural penicillin, given via IV, binds PBP in bacteria to inhibit cell wall synthesis. There is increased resistance due to inactivation by B-lactamase secreted by bacteria that breaks down B-lactam ring in the PCN structure making it inactive.
Active against most gram positive cocci (NOT STAPH), gram positive rods, gram negative cocci and most anaerobes.
Drug of choice:
- Syphillis
- Strep infection (Rheumatic fever prophylaxis)
- susceptible pneumococci
Repository penicillins?
Penicillin G Procaine AND Penicillin G Benzathine
These drugs were developed to prolong the duration of PCN G. They are effective against mainly gram positives (not staph species). Same as PCN G, except delivered via IM NOT IV.
Penicillin G Procaine - IM, half life of 12-24hrs, increased resistance, so is seldomly used
Penicillin G Benzathine - IM, half life of 3-4 weeks
Drug of choice:
- syphilis
- rheumatic fever prophylaxis (strep infection)
Penicillin V?
Natural penicillin, given orally as it is more acid stable than PCN G. It is a bactericidal drug that binds the PBP and inhibits the cell wall synthesis.
Drug of choice:
STREP THROAT– given orally for mild to moderate infections (pharyngitis, tonsilitis, and skin infections caused by Strep)
Anti-staphylococcal PCN?
Methicillin Nafcillin Oxacillin Dicloxacillin [M,N,O,'P'(D)]
Methicillin, Nafcillin, Oxacillin, Dicloxacillin?
Anti-staphylococcal PCN that are B-lactamase resistant (therefore are not broken down by the B-lactamase enzyme) but are inactive against MRSA organisms. These Abx are restricted to treatment of B-lactamase-producing STAPHYLOCOCCI.
Drug of choice:
Staphylococci ENDOCARDITIS in pts without artificial heart valves
*Methicillin is no longer FDA approved as it lead to interstitial nephritis
AE Dicloxacillin - Hypersensitivity / GI / Secondary infections
AE Oxacillin - Hypersensitivity / GI / Hepatitis / Secondary infections
AE Nafcillin - Hypersensitivity / GI / Neutropenia / Secondary infections
Ampicillin and Amoxicillin?
Extended-spectrum penicillins that are similar to Penicillin G, but have enhanced GRAM NEGATIVE activity. They are susceptible to B-lactamases, so generally need to be given with B-lactamase inhibitors.
Amoxicillin has high oral bioavailability compared to other PCNs (including ampicillin) and is prescribed for children and during pregnancy. [Amoxicillin is given orally whereas Ampicillin is given oral, IV or IM]
Used to treat….
- Acute otitis media
- Streptococcal pharyngitis
- pneumonia
- skin infections
- UTIs
* *upper respiratory infections (H. flu and S. pneumo)
Amoxicillin - drug of choice for endocarditis prophylaxis during dental or respiratory tract procedures (ex. protect against Strep viridan driven endocarditis post dental procedure)
AE [Ampicillin] - Hypersensitivity / GI / Maculopapular Rash / Pseudomembranous colitis
AE [Amoxicillin] - Hypersensitivity / GI / Maculopapular Rash / Secondary infections
What drugs are used to treat enterococci and listerial infections?
Ampicillin+aminoglycoside
What drugs are used as prophylactic tx of dog, cat and human bites?
Amoxicillin+Clavulanic
What drugs are used as endocarditis prophylaxis during dental or respiratory procedures?
Amoxicillin
