Which statement correctly describes Methicillin and Dicloxacillin?

Which statement correctly describes Methicillin and Dicloxacillin?

• A. Not penicillinase-resistant
• B. Beta-Lactamase Resistant
• C. They inhibit DNA Synthesis
• D. They have extremely broad Gram-Negative activity

Answer: (B)

Penicillinase resistance is the key idea here. Methicillin and dicloxacillin are penicillinase-resistant (beta-lactamase–resistant) penicillins. Their bulky side chains shield the beta-lactam ring from penicillinase enzymes produced by some bacteria, so the drugs remain active where other penicillins would be inactivated. Because they still share the beta-lactam mechanism, they inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins. Their bulky structure, while protecting them from beta-lactamase, also limits their ability to reach many Gram-negative organisms, giving them mainly activity against Gram-positive bacteria. They do not inhibit DNA synthesis, and they are not characterized by extremely broad Gram-negative coverage.

Penicillinase resistance is the key idea here. Methicillin and dicloxacillin are penicillinase-resistant (beta-lactamase–resistant) penicillins. Their bulky side chains shield the beta-lactam ring from penicillinase enzymes produced by some bacteria, so the drugs remain active where other penicillins would be inactivated. Because they still share the beta-lactam mechanism, they inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins. Their bulky structure, while protecting them from beta-lactamase, also limits their ability to reach many Gram-negative organisms, giving them mainly activity against Gram-positive bacteria. They do not inhibit DNA synthesis, and they are not characterized by extremely broad Gram-negative coverage.