Penicillin, Nafcillin, oxacillin, cloxacillin, and dicloxacillin Flashcards
What is the mechanism of action of penicillin?
Penicillin blocks peptidoglycan synthesis by inhibiting transpeptidases, preventing bacterial cell wall cross-linking.
What are the two major forms of penicillin?
Penicillin G (given IM or IV) and Penicillin V (given PO).
Why is Penicillin V given orally while Penicillin G is given IM/IV?
Penicillin V is acid-stable, allowing it to survive stomach acid, whereas Penicillin G is acid-labile and must be given parenterally.
What type of bacteria does penicillin primarily target?
Gram-positive organisms, spirochetes, and select gram-negative organisms such as Neisseria meningitidis (if susceptible).
How does penicillin interfere with bacterial cell wall synthesis?
It inhibits transpeptidation, preventing peptidoglycan cross-linking and leading to bacterial lysis.
What are the clinical uses of penicillin?
Used for streptococcal pharyngitis (strep throat), rheumatic fever prophylaxis, endocarditis (Strep viridans, Strep bovis), syphilis, Actinomyces, Clostridium perfringens, Pasteurella multocida, and Group B Strep (Strep agalactiae prophylaxis in pregnant women).
Which form of penicillin is used for rheumatic fever prophylaxis?
Benzathine Penicillin G (IM) or Penicillin V (PO).
Which bacteria commonly cause endocarditis that is treatable with penicillin?
Streptococcus viridans and Streptococcus bovis (associated with colon cancer).
What organism causes strep throat (streptococcal pharyngitis) and is treated with penicillin?
Streptococcus pyogenes.
Which organism causes Group B Streptococcal disease and is prevented with penicillin prophylaxis in pregnant women?
Streptococcus agalactiae.
Which gram-positive branching rod is treated with penicillin?
Actinomyces israelii.
Which gram-negative coccobacillus, associated with dog bites, is treated with penicillin?
Pasteurella multocida.
What is the drug of choice for Clostridium perfringens infections?
Penicillin G (IV).
Which spirochete is treated with penicillin?
Treponema pallidum (syphilis).
Which spirochete, associated with water contaminated by animal urine, is treated with penicillin?
Leptospira interrogans.
What are the major side effects of penicillin?
Hypersensitivity reactions (IgE-mediated anaphylaxis), drug rash, autoimmune hemolytic anemia (Coombs positive), and acute interstitial nephritis.
What is the mechanism of resistance to penicillin?
Beta-lactamases (penicillinases) hydrolyze the beta-lactam ring, leading to resistance, particularly in Staphylococcus aureus.
Which enzyme in bacteria is responsible for penicillin resistance?
Beta-lactamase (penicillinase).
What type of hemolytic anemia can penicillin cause?
Autoimmune hemolytic anemia (Coombs positive hemolysis).
What renal complication can occur with penicillin use?
Acute interstitial nephritis.
Which gram-negative diplococcus can penicillin treat if susceptible?
Neisseria meningitidis.
What are the anti-staphylococcal penicillins?
Nafcillin, oxacillin, cloxacillin, and dicloxacillin.
What is the mechanism of action of anti-staphylococcal penicillins?
They covalently bind to penicillin-binding proteins (PBPs), inhibiting peptidoglycan synthesis and disrupting the bacterial cell wall.
Why are anti-staphylococcal penicillins resistant to beta-lactamase?
They have bulky R-groups that prevent beta-lactamase from binding to the beta-lactam ring.
What infections are treated with anti-staphylococcal penicillins?
Methicillin-sensitive Staphylococcus aureus (MSSA) infections, including:
- Skin and soft tissue infections
- staphylococcal endocarditis
- osteomyelitis
Are anti-staphylococcal penicillins effective against methicillin-resistant Staphylococcus aureus (MRSA)?
No, they are ineffective against MRSA due to altered PBPs.
What hypersensitivity reactions are associated with anti-staphylococcal penicillins?
Rash, urticaria, anaphylaxis, serum sickness, and interstitial nephritis.
What renal adverse reaction is commonly associated with anti-staphylococcal penicillins?
Acute interstitial nephritis (AIN).
What hematologic adverse effects are seen with anti-staphylococcal penicillins?
Eosinophilia, thrombocytopenia, and hemolytic anemia (rare).
What hepatic adverse effect is notable with oxacillin?
Elevated liver enzymes (transaminitis).
Why is knowing that nafcillin is primarily eliminated through biliary excretion important?
Biliary excretion reduces the risk of nephrotoxicity compared to other beta-lactams, so this would be the drug of choice for a patient with kidney disease.
What should be monitored during anti-staphylococcal penicillin therapy?
Monitor for hypersensitivity reactions, kidney function, and liver enzymes during prolonged use.
