First generation cephalosporins are active against?
**Core Concept**
First-generation cephalosporins are a class of beta-lactam antibiotics that exhibit a narrow spectrum of activity primarily targeting Gram-positive and some Gram-negative bacteria. Their mechanism of action involves inhibition of cell wall synthesis by binding to penicillin-binding proteins (PBPs) on the bacterial cell wall.
**Why the Correct Answer is Right**
First-generation cephalosporins, such as cefazolin, are effective against most Gram-positive cocci, including Staphylococcus aureus (methicillin-sensitive), Streptococcus pneumoniae, and some Gram-negative bacteria like Neisseria gonorrhoeae and Escherichia coli. This is due to their ability to penetrate into the interstitial fluid and tissues, where they can exert their bactericidal effects. The primary target for these antibiotics is the bacterial cell wall, where they inhibit the cross-linking of peptidoglycan layers, leading to cell lysis and death.
**Why Each Wrong Option is Incorrect**
**Option A:** Not Correct - First-generation cephalosporins have limited activity against Pseudomonas aeruginosa, a common Gram-negative rod.
**Option B:** Not Correct - Second-generation cephalosporins, such as cefuroxime, have a broader spectrum of activity that includes some Gram-negative bacteria, but not to the same extent as third-generation cephalosporins.
**Option C:** Not Correct - Fourth-generation cephalosporins, such as cefepime, have an even broader spectrum of activity that includes many Gram-negative bacteria, but this is not characteristic of first-generation cephalosporins.
**Clinical Pearl / High-Yield Fact**
First-generation cephalosporins are generally safe for use in patients with renal impairment, as they are primarily excreted via the bile, but it is essential to monitor liver function and adjust dosages accordingly.
**Correct Answer: D. Most Gram-positive cocci and some Gram-negative bacteria.**