Pharmacology – Penicillins

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What antibiotics are presumably safe in pregnancy?
Most penicillins, cephalosporins, erythromycin base, aztreonam

What antibiotics should be avoided in pregnancy?
Tetracyclines, quinolones, erythromycin estolate, chloramphenicol, TMP-SMX

Do quinolones have good bioavailability?
Yes, so oral doses and IV doses are comparable

What is the mechanism of action of penicillins?
The beta lactam ring inhibits the final cross linking steps of peptidoglycan synthesis thus inhibiting cell wall synthesis and causing lysis of bacteria

How are most penicillins excreted?
Renal excretion is important for most, so doses must be adjusted in patients with renal insufficiency

What is the drug of choice for Group A strep pharyngitis?
Penicillin V, an oral formulation

What are possible side effects of penicillin use?
Anaphylaxis can occur but is rare (.002%), delayed onset maculopapular rash is more common (2-5%, increases with duration of use), can also cause drug fever. Rarer side effects are interstitial nephritis and myoclonic twitching (high doses in renal failure).

What penicillin would be used for rheumatic fever prophylaxis?
Benzathine penicillin G, maintains low serum levels for 3-4 weeks

What are potential uses of benzathine penicillin G?
Syphilis Rx, Strep A pharyngitis, rheumatic fever prophylaxis

How is benzathine penicillin G administered?
Intramuscular injection (painful)

What organisms is penicillin useful against?
Gram (+) like GAS, viridans strep, Gram (-) like N. meningitides, good for oral anaerobes, but not good for GI anaerobes, active against Treponema pallidum (syphilis)

What organisms are antistaphylococcal penicillins useful against?
MSSA (10% or less of Staph. aureus are susceptible to pencillin), these agents don’t cover MRSA, active against Strep A, not good for Gram (-) or anaerobes

What is the absorption of the antistaphylococcal penicillins?
Oxacillin and Nafcillin both have poor oral absorption and are given IV. Dicloxacillin can be taken PO, but has a poor taste and potential GI discomfort

What is a rare but serious side effect of oxacillin?
Hepatitis

What is a rare but serious side effect of Nafcillin?
Leukopenia

What is the route of administration of amoxicillin?
PO

What is the route of administration of ampicillin?
IV

What is the drug of choice for uncomplicated cases of acute otitis media?
Amoxicillin

What is the drug of choice for uncomplicated cases of sinusitis?
Amoxicillin

What are the common indications for amoxicillin?
Uncomplicated cases of acute otitis media and sinusitis, sometimes used for acute exacerbations of chronic bronchitis and select cases of CAP

What organisms are extended spectrum penicillins like amoxicillin and ampicillin active against?
Gram (+) like GAS, viridans, Gram (-) N. meningitides, oral anaerobes, Treponema pallidum AND (extended spectrum part): H. influenzae (unless resistant), most enterococci (not VRE), decent for community Gram (-), no good for hospital Gram (-)

What are the side effects of amoxicillin and ampicillin?
Anaphylaxis is rare but possible, there is increased risk of maculopapular rash (~10%) compared to prototype penicillins (2-5%). If patient has mono there is a 50% chance of rash

What organisms are anti-pseudomonas penicillins useful against?
Have increased activity against Gram (-) including hospital acquired, including Pseudomonas aeruginosa. Second line agent for anaerobes (even GI)

True or false: anti-pseudomonas penicillins should always be used as monotherapy
False: monotherapy selects resistant organisms rapidly, so synergistic use, with an aminoglycoside for example, is recommended

What type of penicillins can lead to hypokalemia?
Anti-pseudomonas penicillins

What is the drug of choice for dog bites?
Amoxicillin-clavulanate (Augmetin)

What type of penicillin might you use if you’re worried about a mixed aerobic-anaerobic infection?
Beta-lactam, anti-beta-lactamase combination such as Ampicillin-sulbactam (Unasyn), Ticarcillin-clavulanate (Timentin), or Piperacillin-tazobactam (Zosyn)

What penicillin might you use for an aspiration pneumonia?
Aspiration pneumonia is likely to be a mixed aerobic-anaerobic infection, so a combined beta-lactam and anti-beta-lactamase drug would be useful

What penicillin might you use for an intraabdominal/pelvic infection?
Intraabdominal/pelvic infections are likely to be mixed aerobic-anaerobic infetions, so a combined beta-lactam and anti-beta-lactamase drug would be useful

What penicillin could you use in a case of ampicillin resistant H. influenza?
Amoxicillin-clavulanate (Augmentin)

What is the route of administration for anti-pseudomonas penicillins?
IV. If looking to Rx a PO drug, use a quinolone

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