Question

Recognize the following major structures and know how changing the structure will effect the activity (if we discuss any):

Penicillins, Cephalosporins

1. What is the mechanism of action for penicillins and cephalosporins? Is it bactericidal or bacteriostatic? What are the side effects?

2. What is the common structural feature of all penicillins and which is the functional group that is modified?

3. What are the common problems associated with natural pencillins?

4. What does hypersensitivity have to do with chemical reactivity?

5. What is the major mechanism for resistance with the penicillins? List two other mechanisms.

6. What is the structural change that we make to instill beta lactamase resistance? This reduces the activity of these penicillins, what are the three undesirable characteristics. Consider nafcillin as the prototypes. What advantage do oxacillin & dicloxacillin have over nafcillin?

7. What is the normal spectrum of susceptible organisms for pen V, limited (methicillin), broad (ampicillin) and extended (carbenicillin) spectrum penicillins?

Class/Spectrum	Gram (+) coverage	Gram (-) coverage	Beta-lactamase resistant	other
Pen V/traditional	+	- (weak)	-
Methacillin-like/limited or narrow
Carbenicillin/extended				Inc. pseudomonas
Ampicillin/Broad

Answer 1

Since you have posted multiple questions, I am going to answer first two. I hope it helps. Thanks

1.Penicillin acts as a bactericidal antibiotic which kills susceptible bacteria by specifically inhibiting the transpeptidase that catalyzes the final step in cell wall biosynthesis, the cross-linking of peptidoglycan. Cephalosporins are also bactericidal and have the same mode of action as penicillin but are less susceptible to β-lactamases.

2. A four-membereed lactam ring is characteristic of the antibiotics of penicillin family. Various penicillins differ mainly by the structure of the side chain.